NCERT Solutions For Class 10 Science

• Chapter 1 Chemical Reactions And Equations
• Chapter 2 Acids, Bases And Salts
• Chapter 3 Metals And Non-Metals
• Chapter 4 Carbon And Its Compounds
• Chapter 5 Periodic Classification Of Elements
• Chapter 6 Life Processes
• Chapter 7 Control and Coordination
• Chapter 8 How do Organisms Reproduce

• Chapter 9 Heredity And Evolution
• Chapter 10 Light-Reflection 10 And Refraction
• Chapter 11 Human Eye And Colourful World
• Chapter 13 Magnetic Effects Of Electric Current
• Chapter 14 Sources Of Energy
• Chapter 15 Our Environment
• Chapter 16 Management Of Natural Resources

NCERT Solutions For Class 10 Science Chapter 11 Human Eye And Colourful World Long Question And Answers

Question 1. A myopic person has been using spectacles of power- 1.00 D for clear vision. During old age he also needs to use separate reading glasses of power + 2.00 D. Explain what may have happened to Lois’s eyesight.
Answer: When he was using lenses only for myopic defect, his near point was normal i.e., equal to 25 cm.

His far-off off-point was 100 cm according to the power oflens he was using. His eye lens had the normal power of accommodation. Due to old age, his ciliary muscles became weaker and he did not have a normal power of accommodation.

So his near point of vision also increased and reached up to 50 cm as shown below and he needed a lens of 2.00 D power for that purpose.

p=+2.00D of \(f=\frac{1}{\mathrm{P}}=\frac{1}{2}=0.5 \mathrm{~m}=50 \mathrm{~cm}, u=-25 \mathrm{~cm}\)

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Using the lens formula, we have

⇒ \(\begin{aligned}
\frac{1}{v} & =\frac{1}{f}+\frac{1}{u} \\
& =\frac{1}{50}+\frac{1}{-25} \\
& =\frac{1}{-50}
\end{aligned}\)

v=50cm Thus, the near point of this person is 50 cm away from his eyes.

Question 2. The point of a myopic person is 100 cm. Calculate the power of the lens required to enable him to see distant objects. For which colours, is the refractive index n of prism material

1. Minimum
2. Maximum.

Answer: Required focal length, f=- 100 cm =- 1 m or -1m

⇒ \(\begin{aligned}
P & =\frac{1}{f} \\
& =\frac{1}{-1 \mathrm{~m}} \\
& =-1 \mathrm{D}
\end{aligned}\)

1. N is the minimum for red colour.
2. N is the maximum for violet colour.

Question 3. What is astigmatism? How is it caused? How is it corrected? Or What is astigmatism and how is this vision defect counteracted?
Answer: Astigmatism: It is a defect of vision in which a person cannot simultaneously see both the horizontal and vertical views of an object with the same clarity.

Cause of astigmatism:

This defect occurs when the cornea of the eye is not perfectly spherical. This results in objects in one direction being well focussed while those in a perpendicular direction are not well focussed.

Correction of astigmatism: Astigmatism can be corrected by using cylindrical lenses.

They have different curvatures in horizontal and vertical directions so they can be oriented suitably to compensate for the irregularities in the cornea, as shown in the figure.

Question 4. A person with a defective eye-vision is unable to see objects nearer than 1.5 m. He wants to read books at a distance of 30 cm. Find the nature, focal length and power of the lens he needs in his spectacles.
Answer: This person suffers from the defect of hypermetropia.

For him u =- 30 cm, v =- 1.5 m =- 150 cm

Therefore, the focal length of the corrective lens to be used by us

⇒ \(\begin{aligned}
\frac{1}{f} & =\frac{1}{v}-\frac{1}{u} \\
& =\frac{1}{-150}-\frac{1}{-30} \\
& =\frac{4}{150} \text { of } f=37.5 \mathrm{~cm}
\end{aligned}\)

The positive sign shows that the lens needed is a convex lens with a focal length of 37.5 cm. Hence, the power oflens needed

⇒ \(\begin{aligned}
\mathrm{P} & =\frac{1}{f} \\
& =\frac{100}{37.5} \\
& =2.67 \mathrm{D}
\end{aligned}\)

Question 5. Give some points of similarity and dissimilarity between a camera and the human eye.
Answer: Points of similarity:

Points Of Dissimilarity: 

Question 6. In a beautiful valley, there was a village. Train passes from the village, the whistle and the sound of train mixed with the sound of waterfall seemed to be very pleasant to everyone.

Children of that village loved to play near the railway track. One very light foggy day, a group of children found that a fishplate was missing from the track. Knowing this all of the villagers became tense. Aditya, one ofthe kids, suddenly put his ear to the line and tried to know whether the train was coming or not and he knew that the train was coming. He asked his friend to inform the railway cabin crew and he himselfput off his red shirt and started running towards the train, waving his red shirt. Timely, the driver and cabin man got information and a major accident had not taken place.

1. Name the two physical phenomena of science used by Aditya.
2. Why did Aditya use a red shirt instead of other colours?
3. What moral values were shown by Aditya1?

Answer: Sound travels through a medium.

1. Scattering of light.
2. Red is least scattered by fog or smoke so it can be seen from a large distance.
3. Proper knowledge and its application.
4. Concern for each other

Question 7. What is the dispersion of white light? What is the cause of such dispersion? Draw a diagram, to show the dispersion of white light by a glass prism.

A glassprism can produce a spectrum when white light passes through it but a
glass slab does notproduce any spectrum. Explain why it is so

Dispersion: The splitting of light into its constituent seven colours is called dispersion of light.

Cause: Ordinary white light is a superposition of waves of wavelengths extending throughout the visible spectrum. The speed of light in a vacuum is the same for wavelengths, but the speed in a material light substance is different for different wavelengths.

As a result, different colours are deviated by different angles when they pass through a prism. This is called the dispersion of light.

In a prism, the refraction oflight takes place at the two slant surfaces. The dispersion of white light occurs at the first surface of the prism where its constituent colours are deviated through different angles.

At the second surface, these split colours suffer only refraction and they get further separated. But in a rectangular glass block, the refraction of light takes place at the two parallel surfaces.

At the first surface, although the white light splits into its constituent colours on refraction, these split colours suffering refraction at the second surface emerge in the form of a parallel beam, which gives an impression of white light.

Question 8. Discuss the refraction of light through a prism. What are the angle of deviation and angle of emergence? How are these angles related to the angle of incidence and the angle prism? or Draw a ray diagram to show the path of the light ray that enters the glassprism obliquely. Label it the angle of incidence and angle of deviation.

Answer: Refraction through a glass prism: The figure shows the principle section ABC of a glass prism.

Aray PQ is incident on face AB. As it enters the denser medium (glass), it bends away from the normal along path QR.

The ray QR again suffers refraction at face AC; bending away from the normal, it emerges along. The angle between the incident ray and the emergent ray is Incident called the angle of deviation.

The angle e made by the emergent ray with the p normal to the refracting face AC is called the angle of emergency. A light ray bends towards the base ofthe prism as it suffers refraction through the prism. It is seen that ray i+e=A+=D

In other words, Angle of incidence + Angle of emergence = Angle of prism + Angle of deviation

Question 9. The sun near the horizon appears flattened at sunset and sunrise. Explain why?
Answer: Apparent flattening of the sun’s disc at sunrise and sunset: This is due to atmospheric refraction. The density and the refractive index ofthe atmosphere decrease with altitude, so the rays from the top and bottom portion ofthe sun on the horizon are refracted by different degrees.

This causes the apparent flattening of the sun. But the rays from the sides ofthe sun on a horizontal plane are generally refracted by the same amount, so the sun still appears circular along its sides.

Question 10. The sun is visible to us about two minutes before the actual sunrise and about two minutes after the actual sunset. Give reason.
Answer: Advance sunrise and delayed sunset.

The apparent shift in the position of the sun at sunrise and sunset: The sun is visible before actual sunrise and after actual sunset, because of atmospheric refraction. With altitude, the density and hence refractive index of the air-layer decreases.

As shown in the figure, the light rays starting from the sun travel from rarer to denser layers. They bend more and more towards the normal. To an obese on the earth, light rays appear to come from position S’.

The sun which is actually in position S below the horizon, appears in position S’ above the horizon. Thus the river sun appears to rise early by about two minutes and for the same reason, it appears to set late by about two minutes. This increases the length of the day by About Four Minutes

Question 11. Draw a neat labelled diagram of the structure ofthe human eye and mention the functions of any four parts.
Answer: Cornea: Thin transparent membrane which allows the light to enter and refracts
the light to focus it on the crystalline lens.

Crystalline lens: Double convex lens changes its focal length with the help of ciliary
muscles and the suspensory ligaments and enables the light ray to fall on the retina.

Iris: Coloured portion ofthe eye regulates the size of the pupil and controls the amount
oflight entering the eye.

Retina: Consists oflight light-sensitive cells (rod and cone cells) which enable us to see in dim and bright light.

Question 12. What is the Tyndall effect? What is its cause? Name two phenomena observed in daily life which are based on the Tyndall effect.
Answer: Tyndal effect: When a beam oflight is passed through a colloidal solution, and placed in a dark room, the path of the beam becomes illuminated (or visible), when observed through a microscope placed perpendicular to the path oflight.

This effect is called the Tyndall effect. On the other hand, the path of a beam oflight is not visible through a true solution, as shown in the figure

Cause of Tyndall effect: The size ofthe colloidal particle is relatively larger than the solute particle of a true solution. The colloidal particles first absorb energy from the incident light and then scatter a part of this energy from their surfaces. Thus Tyndall effects due to the scattering oflight by the colloidal particles and the colloidal particles are seen as points oflight moving against a dark background.

Some daily life phenomena based on the Tyndall effect are as follows:

When a fine beam of sunlight enters a smoke-filled room through a small hole, the smoke particles become visible due to the scattering flight. When sunlight passes through the canopy of a dense forest, the tiny water droplets in the mist scatter light and become visible.

Question 13. Explain the structure and functioning of the human eye. How are we able to see nearby as well as distant objects?
Answer: The structure and functioning human eye are as given below: Cornea: Cornea is transparent. It is responsible for most ofthe refraction oflight rays towards the retina.

Iris: Iris is a dark, circular muscular diaphragm behind the cornea. It gives the eye its colour. It also controls the pupil size and thus controls the amount oflight entering the eye.

Pupil: Pupil is surrounded by the iris. It regulates and controls the amount of light
entering the eye.

Retina: The retina is the innermost layer of the eye. It contains an outer pigmented layer and an inner nervous layer which contains the photoreceptors (rods and cones). Cone cells are cone-shaped and rod cells are rod-shaped.

Optic nerve: The optic nerve connects the eye to the brain. The nerve fibres carry impulses from the retina to the visual cortex.

Eye lens: The eye lens is made up of fibrous, jelly-like material. It is transparent and has a biconvex structure. It forms an inverted real image of the object on the retina and also separates the aqueous and the vitreous humour.

Vitreous humour: Vitreous humour is clear and semi-solid, supporting the eyeball. The eye lens forms an inverted real image of the object on the retina, which sends image electric signals to the brain via the optic nerves. The brain reconstructs erect images of objects and makes us see them as they are.

Question 14. When do we consider a person to be myopic or hypermetropic? Explain using diagrams how the defects associated with myopic and hypermetropic eyes can be corrected.
Answer: Myopic: This term is used to define short-sightedness. Light from a distant object forms an image before it reaches the retina. This could be because the eye is too long or the cornea or crystalline lens is too strong. A myopic person has clear vision when looking at objects close to them but distant objects will appear blurred.

To correct this defect, a concave lens (minus powered) is placed in front of a myopic eye, moving the image back to the retina and clarifying the image.

Hypermetropic: It means long-sightedness, in which the image of a nearby object is formed behind the retina. This could be because the eye is too short or the cornea or crystalline lens does not refract the light enough.

A hypermetropic person may have blurred vision when looking at objects close to them and clearer vision when looking at objects in the distance.

To correct this defect, a convex lens (plus powered) is placed in front of a hypermetropic eye, and the image is moved forward and focuses correctly on the retina.

Question 15. Explain the refraction oflight through a triangular glass prism using a labelled ray diagram. Hence define the angle of deviation.
Answer: The angle of deviation is the angle D between the incident ray and the emergent ray when a ray oflight passes through a glass prism. Aray oflight PE is entering from air to glass at the first surface AB.

The lightrayEF on refraction has bent towards the normal. At the second surface AC, the light ray FS has entered from glass to air and bent away from normal. The angle made by extending the incident ray with the emergent ray is called the angle of deviation.

Question 16. How can we explain the reddish appearance of the sun at sunrise or sunset? Why does it not appear red at noon?
Answer: The reddish appearance of the sun at sunrise or sunset is due to the scattering oflight by the molecules of air and other fine particles in the atmosphere that have a size smaller than the wavelength of visible light from the sun near the horizon.

It passes through thicker layers of air and a larger distance in the earth’s atmosphere before reaching our eyes and most ofthe blue light and shorter wavelengths are scattered away by the particles.

So, only red light, being of a higher wavelength, reaches us which gives the reddish appearance of the sun at sunrise or sunset.

At noon, the sun appears white, not red, as only a little of the blue and violet colours are scattered as light from the sun overhead would travel relatively shorter distances.

Question 17. Explain the phenomenon of dispersion of white light through a glassprism, using a suitable ray diagram. When white light such as sunlight is passed through a prism it is reduced to a narrow beam.

This narrow beam is made to fall on a triangular glass prism. When a white screen is held on the other side of the prism, we observe a band of seven colours on the screen.

The colour sequence obtained on the screen from its lower end is given by the famous acronym VIBGYOR, where V stands for violet, I stands for Indigo, B stands for Blue, G stands for Green, Y stands for Yellow, O stands for Orange and R stands for Red.

The red colour bends the least on passing through the prism and the violet colour bends through the maximum angle on passing through the prism.

This is why red is at the top and violet is at the bottom. Thus, the phenomenon of splitting white light into its constituent seven colours on passing through a glass prism is known as the dispersion of light.

Question 18. How does refraction take place in the atmosphere? Why do stars twinkle but not the planets?
Answer: The refraction of light by the earth’s atmosphere is due to the gradually changing refractive index of air layers.

The physical conditions ofthe refracting medium (air) are not stationary and the apparent position of the object as seen through the hot air fluctuates. This wavering is thus an effect of atmospheric refraction on a small scale in our local environment.

Since, the atmosphere bends light from the astronomical bodies viz, stars towards the normal, the apparent position of the astronomical bodies is slightly different from its actual position. The astronomical bodies appear slightly higher (above) than their actual position when viewed near the horizon.

The twinkling of a star is due to atmospheric refraction of starlight. The starlight, on entering the earth’s atmosphere, undergoes refraction continuously before it reaches the earth.

The path of rays oflight coming from the distant star goes on varying slightly, the apparent position ofthe star fluctuates and the amount of starlight entering the eye flickers such that the star sometimes appears brighter and at some other times fainter which gives us the twinkling effect.

Question 19. News spread in the school that a student of class IX-A had died due to a heart attack, but he donated his beautiful eyes to one of his friends.

All the members of the school felt very sad about his untimely death, but on the other hand, they were overwhelmed upon hearing the donation of his eyes to his friend, who would now be able to see this beautiful nature. Answer the following questions based on the situation given above.

Do you think that the student who expired had done a good job? Is it worth to donate
vital organs?

1. What values are promoted here?
2. What other organs can be donated after dying?

Answer: Yes. Donating vital organs can make the life of a living person easier.

1. Social welfare, kind-hearted, selfless, friendship.
2. Kidneys, heart, liver, etc.

Question 20. ‘Sonia and Soya’ are best friends and study in grade 4. Recently, Sonia has been facing difficulty in reading the blackboard text from the last desk. Soya is a little uncomfortable and wonders why Sonia complains about sitting at the last desk.

On observation, she found that Sonia often carries junk food in her lunch. Soya has started sharing her lunch full of green vegetables and fruits with her. Sonia is now better and has also started taking a ‘balanced diet’.

Answer the following questions based on the above situation:

Name the eye defect Sonia is suffering from. What are the two possible reasons related
to her eye defect?

1. What value is displayed by Soya and Sonia?
2. How can this value be promoted? Suggest one activity.

Answer: Myopia/short-sightedness. Lens defect (increased thinness), eyeball defect
(elongation).

Friendship, concern for each other, and appreciation for a balanced diet.

Sharing common things; Helping each other in studies.

Question 21. While boating with parents a child saw a beautiful fish in the lake. He tried to catch it, thinking that it was very close to the boat. His parents told him that the fish were deep in the water and he should not try to catch them. But he did not listen to them and the situation came when he fell into the lake instead of catching it.

Answer the following:

1. Why did the fish appear closer to the boat when it was deep in the water?
2. What values are neglected by the child?

Answer:

This is due to the phenomenon of refraction. Light reflected from the fish travels through the water towards the eye.

As it passes from the water into the air, it refracts away from the normal because water is denser than air and thus, the fish appears closer. Obeying elders, being careful, and understanding reasons for natural phenomena.

NCERT Solutions For Class 10 Science Chapter 10 Light-Reflection And Refraction

Question 1. Which lens can be used as a magnifying glass?

For which position  of an object does a convex lens form:

1. A virtual and erect image?
2. A real and inverted image of the same size as that of an object? Dlabeled ray diagrams to show the formation of the required image in each of the above two cases.

Answer:

A convex lens can be used as a magnifying glass.

1. When an object is between optical center C and focus F₁.

2. Wan a hen object is at 2F₁.

Question 2.

1. Wrthe the ite relation between u, v, and f for lens and for mirrors, where u, v, f are object distance, image dist, ance, and focal length respectively.
2. The magnification produced by a plane mirror is m = + 4. Write the information about the image given by this statement.
3. Draw a ray diagram for the following and show the formation of the images in case of
   concave mirror when the object is placed in:
   1. Between the pole and focus point the center of curvature

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Answer:

1. Mirror formula \(\frac{1}{f}=\frac{1}{v}+\frac{1}{u}\)
   1. Lens formula \(\frac{1}{f}=\frac{1}{v}-\frac{1}{u}\)
2. It means the height of the image is 4 times the height of the object of the image is virtual.
3. (1) Between the pole and focus point

2. The center of curvature

Question 3.

1. Under what condition, does a concave produce a virtual and magnified image? Dralabeledlled ray diagram to show the formation of image in the above case. Also, state the position of the object to provide a magnified and real image.
2. A ray of light moving along one principal axis is falling on a concave mirror. Draw the path the of reflected ray. Also, state the values of the angle of incidence and reflection in this case.

Answer:

1. The hen object lies between the focus and the pole of a mirror or with the focus of a concave mirror case.

The image formed will be real and magnified when the hen object is placed between C and F.

2. The diagram is as shown:

3. i = 0°, r = 0°

Question 4. A 2.0 cm tall object is placed perpendicular to the principal axis of a convex lens of focal length 10 cm. The distance of the object from the lens is 15 cm. Find the proposition and the size of the image forms.
Answer:

Given O = 2.0 cm, f= + 10 cm, u = – 15 cm, v = ?, I = ?

Using the lens formula, \(\frac{1}{v}-\frac{1}{u}=\frac{1}{f}\), we have

⇒ \(\frac{1}{v}=\frac{1}{f}+\frac{1}{u}=\frac{1}{10}+\frac{1}{-15}=\frac{3-2}{30}=\frac{1}{30} \quad \text { or } \quad v=30 \mathrm{~cm}\)

The image is formed on the other side of the lens at 30 cm from it.

⇒ m = \(=\frac{\mathrm{I}}{\mathrm{O}}=\frac{v}{u} \quad \text { or } \quad \mathrm{I}=\frac{v}{u} \times \mathrm{O}=\frac{30}{-15} \times 20=-4 \mathrm{~cm}\)

The negative sign shows that the image is real and inverted.

Question 5.

1. A thin converging lens forms a:
   1. Real magnified image.
   2. Virtual magnified image of an object placed in front of it. Write the positions of the objects in each case.
2. Dlabeledlled ray diagrams to show the image formation in each case.
3. How will the following be affected on cutting this lens the halves along the principal axis:
   1. Focal length intensity of the image formed by the half lens.

Answer:

1. (1) Between F and 2F of a lens.

(2) Within the focal length.

2.

3. No effect on focal length, but intensity decreases.

Question 6. An object 3.0 cm high is placed perpendicular to the principal axis of a concave lens of focal length 7.5 cm. The image is formed at a distance of 5.0 cm from the lens. CalculThe distance

1. ance at which the object is placed, and
2. Size and nature of image formed.

Answer:

Given O = 3.0 cm, f = −7.5 cm, v = 5.0 cm, u = ?, I = ?

Using lens formula, \(\frac{1}{v}-\frac{1}{u}=\frac{1}{f}\) we have

⇒ \(\frac{1}{u}=\frac{1}{v}-\frac{1}{f}=\frac{1}{-5}-\frac{1}{-7.5}=-\frac{1}{15} \quad \text { or } \quad u=-15 \mathrm{~cm}\)

The object is placed 15 cm from the concave lens.

Also, m = \(m=\frac{\mathrm{I}}{\mathrm{O}}=\frac{v}{u}\)

⇒ \(\mathrm{I}=\frac{v}{u} \times \mathrm{O}=\frac{-5.0}{-15.0}\) x 3.0

= 1 cm.

The image is virtual and erect and has a size of 1 cm.

Question 7.

1. A concave mirror produces a three-times enlarged image of an object at 10 cm in front of it. Calculate the focal length of the mirror.
2. Show the formation of the image with the help of a ray diagram when the object is placed 6 cm away from the pole of a convex mirror.

Answer:

1. Given m=-3 (Real image), u = — 10 cm, f=?

Now,

m =\(m=\frac{-v}{u}\)

Therefore, \(-3=\frac{-v}{u} \quad \text { or } \quad v=3 u=-30 \mathrm{~cm}\)

Using the mirror formula, we have

⇒ \(\frac{1}{f}=\frac{1}{-30}+\frac{1}{-10}=\frac{1}{7.5}\)

Therefore, f= -7.5 cm

2. The ray diagram is as shown:

Question 8.

1. State laws of refraction.
2. A ray of light enters from medium A into a slab made up of a transparent substance B (as shown in the figure). Refractive indices of medium A and B are 2.42 and 1.65 respectively. Complete the path the of ray of light till it emerges out of the slab.

Answer:

1. The two laws are:
   1. The incident ray, the refracted, ray, and the normal to the interface of two transparent media at the point of incidence, all lie in the same plane.
   2. The ratio of the sine of the angle of incidence to the there other t angle of refraction is constant, for the light of a color and the given pair of media. This law is also known as Snell’s law of refraction.
2. The path of rays is as shown the in figure:

Question 9.

1. Write one use of a concave mirror as well a as convex mirror.
2. Draw ray diagrams for the following cases when a ray of light:
   1. Passing through the center of curvature of a concave mirror is incident on it. Parallel thee the principal axis is incident an on a convex minor. an an 
   2. Is an incident at the pole of a convex minor.
   3. Passing through the ugh focus of a concave mirror incident on it.

Answer:

1. Concave mirrors are commonly used in torches, search, gets, and vehicle and es, headlights to a get powerful parallel beam of light. Convex mirrors are commonly used rear-view view mirrors in vehicles.
2. The ray diagrams are shown below:

Question 10.

1. Draw a ray diagram in each of the following cases to show the position and nature of the image formed with the hen object is placed:
   1. Between the focus centimeter of curvature of a concave mirror.
   2. Between the een focus the pole of a concave mirror.
   3. BeBetweenhe een center curvature and infinity for a concave mirror.
2. Give mathematical formulae for determining magnification produced by a spherical mirror. What does m = 1 signify? Identify the mirror that can produce it.

Answer:

1. The ray diagrams are as shown:

2. Magnification (m) = height of image, height of object= \(\frac{v}{u}\) m = -1 signifies:

1. size of image = size of objeThe negative sign indicates that the image is real and inverted. A concave mirror ran an or when that is the the the the at center of curvature.

Question 11.

1. The principal focus of a concave mirror
2. Why do we prefer a convex mirror as a rearview mirror in vehicles?
3. We wish to obtain an erect image of an object using a convex lens. Draw a ray diagram to show the image formation in this case.

Answer:

1. Principal focSeveralr of r parallel to the principal axis, after reflection from a concave mirror, meets at a point on the principal axis which is called the principal focus.
2. Conmirrorsrror always gives an erect though diminished image. They have a wider field of view as they are curved outwards and hence the driver can view a much larger area.
3. The diagram is as shown:

Question 12.

1. Describe an activity to find the approximate value of the focal length of a concave mirror.
2. What happens to the size of the image of an object when it is moved gradually away from a convex minor?
3. In an experiment to study refraction through a glass slab, it is observed that a ray of light undergoing refraction emerges parallel to the direction the of incident ray. Why does it happen so? Explain with the help of a diagram.

Answer:

1. Activity: Hold a concave mirror in your hand and direct it towards the screen. Direct the light reflected by the mirror onto a sheet of paper held close to the mirror.

Move the sheet back and forth slowly until a bright, sharp spot of light is seen on the paper. The distance of this image from the position of the mirror gives the approximate value of the focal length of the mirror.

2. The size of the image becomes smaller.

3. The extent of bending of the ray of light at the opposite parallel faces PQ (air-glass interface) and SR (glass air interface) of the rectangular glass slab is equal and opposite.

Question 13. Draw ray diagrams showing the image formation by a concave mirror when an object is placed

1. Betwthe een pole the and focus of the mirror
2. Between the focus centimeter of curvature of the mirror the 
3. At the centre of curvature of the mirror
4. A little better center of curvature of the mirror
5. At infinity

Answer:

The enlarged, vir, virtual, and erect image forms behind the mirror when the object is placed between the pole the and focus of the mirror.

The enlarged, real, and inverted image forms by the center of curvature when the object is placed between the eye focus and the centimeter of curvature of the mirror.

The real and inverted images equal to the size the the of object form the the center of curvature when the object is placed at centimeters of curvature of the mirror.

The diminished, real, and inverted image forms the center of curvature and focuses when the object is placed a little bit on the center of curvature of the mirror.

The real, I’ve rated, and highly reduced image forms at focus F when the object is placed at infinity.

Question 14. Draw ray diagrams showing the image formation by a convex lens when an object is placed

1. Betwthe een optical center and focus of the lens
2. Between focus and twice the focal length of the lens
3. At twice the focal length of the lens
4. At infinity
5. At the focus of the lens

Answer:

The enlarged, virtual, and erect image forms beyond 2F₁ on the same side of the object when the object is placed between the optical center and focus F₁ of the lens.

The enlarged, real, and inverted image forms beyond focus 2F₂ on the other side of the object, when the object is placed between focus F₁ and twice the focal length of the lens.

The real and inverted images equal to the size of the object format focus 2F₂ on the other side of the object when the object is placed at twice the focal length of the lens.

The real, rated, and highly reduced image forms at focus F₂ on the other side of the object when the object is placed at infinity.

The real, rated, and highly magnified image forms at infinity on the other side of the object when the object is placed at the focus of the lens.

Question 15. Write laws of refraction. Explain the same with the help of a ray diagram, when a ray of light passes through a rectangular glass slab.
Answer:

The following are the laws of refraction of light:

1. The incident ray, the refracted, ray, and the normal to the interface of two transparent media at the point of incidence, all lie in the same plane.
2. The ratio of the NE of the angle of incidence to the sine of the angle of refraction is constant, for the light of a colorlour for the given pair of media. This law is also known as Snell’s law of refraction the constant is called the refractive index. The ray diagram. is as shown.

In a rectangular glass slab, the emergent rays are parallel to the incident ray because the extent of bending of the ray of light at the opposite face of the rectangular glass slab is equal and opposite so that the emergent ray is parallel to the incident ray.

Question 16. Draw ray diagrams showing the image formation by a concave lens when an object is placed

1. Between focus and twice the focal length of the lens
2. Beyond twice the focal length of the lens.

Answer:

The image formed is virtual, erect, diminished in, tween optical, and focus F when the object is placed between focus and twice the focal length of the lens.

The image formed is virtual, erect, diminished n,    and between the een optical cent center focus F when the object is placed beyond twice the focal length of the lens.

Question 17. Draw ray diagrams showing the image formation by a convex mirror when an object is placed

1. At infinity a 
2. At a finite distance from the mirror

Answer:

The virtual, erect, and highly diminished image of the object forms at focus F behind the mirror when the object is placed at infinity.

The virtual, erect, and diminished image forms between focus F and pole P behind the mirror when the object is placed a at finite distance from the mirror.

Question 18. The image of a candle flame formed by a lens is obtained on a screen placed on the other side of the lens. If the image is three times the size of the flame and the distance between the lens and the image is 80 cm, at what distance should the candle be placed from the lens? What is the nature of the image at a distance of 80 cm from the lens?
Answer:

The image is real as only the real image can be taken on the screen

Here, image distance, v = 80 cm

Magnification, m = −3

Object distance, u =?

∵ Magnification, m = \(=\frac{v}{u}\)

⇒ -3 \(=\frac{80}{u} \Rightarrow u=-\frac{80}{3} \mathrm{~cm}\)

Nature of image: Real, inverted, magnified, formed beyond 2F

Using the lens formula, we have

⇒ \(\frac{1}{v}-\frac{1}{u}=\frac{1}{f}\)

⇒ \(\frac{1}{f}=\frac{1}{80}-\frac{3}{-80}=\frac{4}{80}=\frac{1}{20}\)

f = 20 cm

Positive focal length denotes that the hat lens is convex.

Question The sizeSizethe the of image of an object by a mirror having a focal length of 20 cm is observed to be reduced to 1/ofofd to its size. At what distance, the object has been placed from the mirror? What is the nature of the image and the mirror?
Answer:

For concave mirror:

Focal length,

f = -20 cm

Magnification, \(m=-\frac{1}{3}\)

∵ \(m=-\frac{v}{u}\)

⇒ \(m=-\frac{1}{3}=-\frac{v}{u}\)

⇒ \(v=\frac{u}{3}\)

Use the ing mirror formula,

⇒ \(\frac{1}{v}+\frac{1}{u}=\frac{1}{f}\)

⇒ \(\frac{1}{f}=\frac{1}{u}+\frac{3}{u}=\frac{4}{u}\)

u = 4f = 4(-20)

= – 80 cm

The object should be placed at a distance of 80 cm from the concave mirror.

For convex mirror:

Focal length, f = + 20 cm

Magnification, \(m=-\frac{v}{u}\)

⇒ \(m=+\frac{1}{3}=-\frac{v}{u}\)

⇒ \(v=-\frac{u}{3}\)

Mirror formula:

⇒ \(\frac{1}{v}+\frac{1}{u}=\frac{1}{f}\)

⇒ \(\frac{1}{f}=-\frac{3}{u}+\frac{1}{u}=-\frac{2}{u}\)

u = − 2f = − 2(20)

= – 40 cm

The object should be placed at a distance of a nice 40 cm from the convex mirror to face an orm virtual, erect, and diminished image.

Question 20. Define the ine power of a lens. What is its unit? One student uses a lens with an h focal length of 50 cm and another of -50 cm. What is the nature of the lens and its power used by each of them?
Answer:

Power of lens: It is defined as the ability of a lens to bend the rays of light. It is given by the reciprocal of focal length. Its unit is dioptre.

If focal length, ƒ = 50 cm, then

⇒ \(\mathrm{P}=\frac{100}{f}=\frac{100}{50}\) = 2 D, lens is convex.the

If the focal length, f= -50 cm, then

⇒ \(\mathrm{P}=\frac{100}{f}=\frac{100}{-50}\) = -2 D, lens is concave.

Question 21. A student focussed the image of a candle flame on a white screen using a convex lens. He noted down the position of the candle, the lens as under:

Position of candle = 12.0 cm

Position of convex lens = 50.0 cm

Position of the screen = 88.0 cm

1. What is the focal length of the convex lens?
2. Where will the image be formed, if he shifts the candle towards the lens at a position of 31.0 cm?
3. What will be the nature of the image formed if he further shifts the candle towards the lens?
4. Draw a ray diagram to show the formation of the image in the case as said above.

Answer:

Object distance, u = Position of the convex lens – Position of the candle = 50 cm – 12 cm = 38 cm

By sign convention, v = +38 cm

1. Using lens formula, \(\frac{1}{v}-\frac{1}{u}=\frac{1}{f}\)

⇒ \(\frac{1}{f}=\frac{1}{38}-\frac{1}{-38}=\frac{2}{38}=\frac{1}{19}\)

The focal length of the convex lens is 19 cm.

2. After shifting the candle towards the lens at a position of 31 cm, then

Object distance, u = Position of convex lens – position of candle = 50 cm -31 cm = 19 cm

By sign convention, u = -19 cm

So, the candle lies at the focus of the lens, hence its image forms at infinity.

3. When the student further shifts the candle towards the lens, the lens foan enlarges, a viral and erect image of the candle.

4. The ray diagram showing the formation of the

Question 22. The angle between an incident ray and the mirror is shown below. The total angle turned by the ray of light is 70°. What is the value of θ?

Answer:

The ray diagram is redrawn as shown below. Since the angle of incidence reflection, therefore, θ = 90° – 35° = 55°.

Question 23. What are two types of reflection?
Answer:

1. Regular
2. Irregular

Question 24. The characteristics of the image formed by a plane mirror.
AnswThe image

1. image is virtual.
2. The size is the same as that of the object.
3. It is formed at the same distance.

Question 25. Give uses of concave mirrors.
Answer:

1. Used as reflectors in car headlights, search, rights, etc.
2. Used as a shaving mirror.
3. Used the solar cooker to focus the sunlight on one point.

Question 26. the  In case of a convex mirror, if the object is moved away from the surface of the mirror, how does the position and size of the image change?
Answer:

As the object is moved away from a convex mirror, the distance of the virtual image, formed behind it, from the mirror increases (between pole and focus) i.e., the image shifts from the pole towards the focus, and the size the of image gradually decreases. When the object is at infinity (very far), the image is at its focus.

Question 27. An object is brought towards a concave mirror. How does the position and size of the image change?
Answer:

When the object is at infinity from the concave mirror, the image is at the focus and it is a diminished and inverted image.

• As the object is brought towards the mirror the image shifts away from the mirror and its size increases.
• When the object is the centimeter of curvature of the mirror, the image is also at cent centimeter curvature and it is of size equal to the size the of object.
• By further bringing the object toward the mirror, the image gets magnified and it moves away from centimeters of curvature.
• When the object is at the focus of the mirror, the image is at infinity. If the object is further moved towards the mirror, the image now becomes erect and magnified and it is formed behind the mirror.

Question 28. Which is a better reflector: A plane mirror right-angled prism?
Answer: A right-angled prism is a better reflector because light incident on its hypotenuse is reflected without absorption of light. On the other hand, in the case of a plane mirror, there is a possibility of partial absorption of light.

Question 29. A convex mirror used for rear-view on an automobile has a radius of curvature of 3.00 m. If a bus is located 5.00 m from this mirror, find the position, nature, and size of the image.
Answer:

Radius of curvature, R = +3.00 cm, (R is +ve for a convex mirror)

Object distance, u = -5.00 m

Image distance, v =?

Height of the image, h′ =?

Focal length, \(f=\frac{\mathrm{R}}{2}=+\frac{3.00 \mathrm{~m}}{2}=+1.50 \mathrm{~m}\)

As \(\frac{1}{v}+\frac{1}{u}=\frac{1}{f}\)

∴ \(\frac{1}{v}=\frac{1}{f}-\frac{1}{u}=+\frac{1}{1.50}-\frac{1}{(-5.00)}=\frac{1}{1.50}+\frac{1}{5.00}=\frac{5.00+1.50}{7.50}\)

⇒ \(v=\frac{+7.50}{6.50}\) = +1.15 m

The image is 1.15 m at the back of the mirror.

Magnification,

m = \(\frac{h^{\prime}}{h}=-\frac{v}{u}=-\frac{1.15 \mathrm{~m}}{-5.00 \mathrm{~m}}\) = +0.23

The image is virtual, erect, and smaller in size by a factor of 0.23.

Question 30. An object, 4.0 cm in size, is placed at 25.0 cm in front of a concave mirror of a focal length of 15.0 cm. At what distance from the mirror should a screen be placed to obtain a sharp image? Find the nature and the size of the image.
Answer:

Object size, h = +4.0 cm

Object distance, u = -25.0 cm

Focal length, f= -15.0 cm

Image distance, v =?

Image size, h’ =?

As \(\frac{1}{u}+\frac{1}{v}=\frac{1}{f}\)

∴ \(\frac{1}{v}=\frac{1}{f}-\frac{1}{u}=\frac{1}{-15}-\frac{1}{-25}=-\frac{1}{15}+\frac{1}{25}\)

or  \(\frac{1}{v}=\frac{-5+3}{75}=\frac{-2}{75}\)

or V =-37.5 cm

The screen should be placed 37.5 cm from the mirror on the object side of the mirror to obtain a sharp image.

Magnification, \(m=\frac{h^{\prime}}{h}=-\frac{v}{u}\)

Image size, h’= \(-\frac{v h}{u}\)

⇒ \(\frac{(-37.5 \mathrm{~cm})(+4.0 \mathrm{~cm})}{(-25 \mathrm{~cm})}\)

= -6.0 cm

The image is real, inverted, and enlarged in size.

Question 31. A concave lens has a focal length of 15 cm. At what distance should the object from the lens be placed so that it forms an image 10 cm from the lens? Also, find the magnification produced by the lens.
Answer:

A concave lens always forms a virtual, erect image on the same side of the object.

Image distance, v = -10 cm

Focal length, f = −15 cm

Object distance u =?

If is -ve for a concave lens

By lens formula, \(\frac{1}{v}-\frac{1}{u}=\frac{1}{f}\)

∴ \(\frac{1}{u}=\frac{1}{v}-\frac{1}{f}=\frac{1}{-10}-\frac{1}{-15}=\frac{-3+2}{30}=-\frac{1}{30}\)

or u = -30 cm

Thus, the object should be placed 30 cm from the lens on the left side.

Magnification, \(m=\frac{v}{u}=\frac{-10}{-30}=+\frac{1}{3}\)= +0.33

The positive sign shows that the image is erect and virtual. The image is reduced to one-third in size than the object.

Question 32. A 2.0 cm tall object is placed perpendicular to the principal axis of a convex lens of focal length 10 cm. The distance of the object from the lens is 15 cm. Find the nature, position, and size of the image. Also find its magnification.
Answer:

Height of the object, h = +2.0 cm

Focal length, f= +10 cm

Object distance, u = -15 cm

If is +ve for a convex lens]

Image distance, v =?

Height of the image, h’=?

By lens formula; \(\frac{1}{v}-\frac{1}{u}=\frac{1}{f}\)

∴ \(\frac{1}{v}=\frac{1}{u}+\frac{1}{f}\)

or \(\frac{1}{v}=\frac{1}{(-15)}+\frac{1}{10}\)

⇒ \(\frac{1}{v}=-\frac{1}{15}+\frac{1}{10}\)

⇒ \(\frac{1}{v}=\frac{-2+3}{30}=\frac{1}{30}\)

or v = +30 cm

The positive sign of u shows that the image is formed at a distance of 30 cm on the other side of the optical center. The image is real and inverted.

Magnification, \(m=\frac{h^{\prime}}{h}=\frac{v}{u}\)

∴ \(m=\frac{v}{u}=\frac{+30 \mathrm{~cm}}{-15 \mathrm{~cm}}=-2\)

Also image size,

h’= \(h^{\prime}=\frac{v h}{u}\)

⇒ \(=\frac{(+30)(+2.0)}{-15}\)

= -4.0 cm

The negative sign of m shows that the image is inverted and real.

It is formed below the principal axis. Thus, a real, inverted image, 4 cm tall, is formed at a distance of 30 cm on the other side of the lens. The image is two times enlarged.

NCERT Solutions For Class 10 Science Chapter 4 Carbon And Its Compounds Long Question And Answers

Question 1.

1. What are homologous series of compounds? List any two characteristics of a homologous series.
2. What would be observed by adding a 5% solution of alkaline potassium permanganate drop by drop to warm ethanol taken in a test tube? Write the name of the compound.
3. How would you distinguish experimentally between an alcohol and a carboxylic acid on the basis ofa chemical property?

Answer:

1. Homologous series represent different families of organic compounds into which these are divided. Two characteristics of homologous series are listed.

• All the members in a particular homologous series of families have the same
  characteristic functional group. For example, in organic acids, the functional
  group is the carboxyl group (—COOH).
• Any two consecutive members in a particular family have the same common difference of CH₂ in their molecular formulae.
• For example, the first three members ofthe family of alkanes are CH₄ (methane), C₂H₆ (ethane), and propane (C₃H₈).

Read and Learn More Class 10 Science Solutions

2. On adding a 5% solution of alkaline potassium permanganate to ethanol, it will be oxidized to ethanoic acid. The pink color of the solution will be discharged upon warming.

3. A carboxylic acid gives a brisk effervescence when an aqueous solution of sodium hydrogen carbonate (NaHCOa) is added to it. This is due to the evolution of CO₂ gas. However, alcohol will not give any reaction.

⇒ \(\underset{\text { Carboxylic acid }}{\mathrm{ROOH}}+\mathrm{NaHCO}_3 \longrightarrow \underset{\text { Sodium salt }}{\mathrm{RCOONa}}+\mathrm{H}_2 \mathrm{O}+\mathrm{CO}_2\)

Question 2.

1. Give a name to the reaction which takes place between ethanoic acid and ethanol in the presence ofconcentrated sulphuric acid. Write the chemical reaction and name of the product obtained.
2. Explain the following reactions with chemical equations:
   1. Oxidation
   2. Hydrogenation
   3. Substitution

Answer:

1. Esterification:

Ethyl ethanoate is the product formed.

2. Oxidation: Alcohols are converted into carboxylic acid in the presence of oxidizing agent

3. Hydrogenation: Hydrogen reacts with unsaturated hydrocarbonin the presence of catalyst.

4. Substitution: Saturated hydrocarbon reacts with chlorine in the presence of sunlight.

CH₄+Cl₂→ CH₃Cl + HCl

Question 3.

1. How is vinegar made?
2. What is glacial acetic acid1? What is its meltingpoint?
3. Write the name and the formula of the two compounds formed when the ester
4. CH₃COOC₅H₂undergoes saponification.

Answer:

1. Acetic acid in water, 5-8% solution.
2. Pure ethanoic acid, 290 K.
3. Do not ionize completely.
4. CH₃COONa or sodium ethanoate; C₂H₅OH or ethanol.

Question 4. A compound X is formed by the reaction ofa carboxylic acid C₂H₄CO₂ and alcohol in the presence ofa few drops of H₂SO₄. The alcohol on oxidation with alkaline KMnO₄ followed by acidification gives the same carboxylic acid as used in this reaction. Give the names and structures of

1. Carboxylic acid
2. Alcohol, and
3. The compound X.

Also, write the reaction.
Answer:

1. Carboxylic acid as ethanoic acid.
2. Alcohol is ethanol.
3. X is ethyl ethanoate.

⇒ \(\underset{\text { Ethanoic acid }}{\mathrm{CH}_3-\mathrm{COOH}}+\underset{\text { Ethanol }}{\mathrm{C}_2 \mathrm{H}_5 \mathrm{OH}} \longrightarrow \underset{\text { Ethyl ethanoate }}{\mathrm{CH}_3-\mathrm{COOC}_2 \mathrm{H}_5}+\mathrm{H}_2 \mathrm{O}\)

Question 5.

1. In organic compounds, which part largely determines the physical and chemical
   properties.
2. Write a chemical equation to represent the reaction of ethanol with the acidified solution of potassium dichromate.

Answer:

1. In organic compounds, it is the functional group that largely determines the physical and chemical properties of compounds. An organic compound is made up of two parts. These are the alkyl group and the functional group.

Whereas the alkyl group remains the same (size may change) the functional groups change. These are responsible for the characteristics of the compounds.

For example, the properties. Alkanols (-OH is the functional group) are different from those of alkanoic acid (-COOH is the functional group).

2. An acidified solution of potassium dichromate (K₂Cr₂O₇) forms chromic acid (H₂CrO₄). It releases oxygen to bring about the oxidation of ethanol first to ethanal and then to ethanoic acid.

Question 6. An ester has the molecular formula C₄H₈O₂ Write its structural formula. What happens when this ester is heated in the presence ofsodium hydroxide solution? Write the balanced chemical equation for the reaction and name the products. What is the saponification reaction?
Answer:

For the molecular formula C₄H₈O₂ two isomeric esters are possible which differ in structural formula. These are

Both will react with sodium hydroxide upon heating from the sodium salt of the acid and alcohol

1. Ethyl ethanoate:

2. Methyl Propanoate:

Question 7.

1. How will you bring about the following reactions’? Write the concerned chemical equation:

1. Ethanol to Ethene
2. Ethanol to Ethanoic acid

2. Give one example with a chemical equation for the following reactions:

1. Substitution reaction
2. Saponification reaction
3. Combustion reaction

Answer:

Question 8. An organic compound A on heating with cone. H₂SO₄ forms a compound B which on the addition of one mole of hydrogen in the presence of nickel forms a compound ‘C’ One mole of ‘C’ on combustion forms 2 moles of CO₂ and 3 moles of H₂O. Identify the compounds A, B, and C and write the equations for the reactions involved.
Answer:

A-Ethanol

B-Ethene

C-Ethane

Question 9. What are soaps chemically? How do they differ from synthetic detergents? Explain the mechanism and the cleaning action of soap.
Answer:

1. Soap: It is sodium or potassium salt of fatty acid.

Detergents are ammonium or sulphonate salts of long-chain carboxylic acids.

2. Due to micelle formation, ionic-ionic repulsion.

Micelle: It is a structure formed when soap molecules get arranged and aligned along the surface of water with the ionic end in water and the hydrocarbon ‘tail’ protruding out of water.

Question 10.

1. A compound burns with a sooty flame. Is it saturated or unsaturated?
2. With the help of suitable tests, distinguish between ethyl alcohol and acetic acid experimentally.

Answer:

1. Organic compounds mostly contain carbon and hydrogen. Both of them burn in the air to form carbon dioxide and water respectively.

If the combustion is complete, this means that all the carbon atoms present in the compound have fully reacted to form carbon dioxide. In case, the flame is sooty, this means that the combustion is incomplete and there are unburnt carbon particles.

Now, a saturated compound like hexane (C₆H₁₄) has more hydrogen atoms as compared to hexene (C₆H₁₂) which is unsaturated. Both have six carbon atoms in their molecules.

Hexane will require more air or oxygen for complete combustion than hexane. Thus, we may conclude that generally, a saturated compound is more likely to burn with sooty flame as compared to an unsaturated compound.

2. The distinction can be made by the following test: Litmus test. Add a few drops of blue litmus solution in two test tubes containing ethyl alcohol and acetic acid. Its color will change to red in the acid while it will remain unaffected in alcohol.

Sodium hydrogen carbonate test. The distinction can also be made with sodium hydrogen carbonate (NaHCO₃).

⇒ \(\mathrm{CH}_3 \mathrm{COOH}+\mathrm{NaHCO}_3 \longrightarrow \mathrm{CH}_3 \mathrm{COONa}+\mathrm{H}_2 \mathrm{O}+\underset{\text { (effervescence) }}{\mathrm{CO}_2}\)

Question 11.

1. Differentiate between soap and detergent.
2. Explain why, soaps form scum with hard water whereas detergents do not

Answer:

2. Hard water contains ions of calcium and magnesium which react with soap molecules to form insoluble precipitates called soap scum.

⇒ \(\underset{\text { Soap molecule (Sodium stearate) (from hard water) }}{2 \mathrm{C}_{17} \mathrm{H}_{35} \mathrm{COONa}}+\mathrm{Ca}^{2+}\left(\mathrm{Mg}^{2+}\right) \longrightarrow \underset{\begin{array}{c}
\text { White ppt.)(scum) } \\
\text { Calciumstearate }
\end{array}}{\left(\mathrm{C}_{17} \mathrm{H}_{33} \mathrm{COO}\right)_2 \mathrm{Ca}}+2 \mathrm{Na}^{+}\)

Question 12. Two carbon compounds ‘A’and ‘B’have the molecular formula C₃H₈ and C₃H₆ respectively. Which one of the two is most likely to show additional reactions? Justify your answer. Explain with the help of a chemical equation, how an addition reaction is useful in the vegetable ghee industry.
Answer:

The compound ‘A’ with the formula C₃H₈ (propane) is a saturated hydrocarbon and corresponds to the general formula C_nH_2n+2. The compound ‘B’ with formula C₃H₆ (propene) is an unsaturated hydrocarbon and corresponds to the general formula C_nH_2n. It has a double bond (C = C) and is, therefore, unsaturated.

The compound ‘B’ will take part in the addition reactions. As a result, the double bond will change to a single bond.

For example,

The addition reaction is quite useful in the hydrogenation of oils i.e., to convert edible oils like groundnut oil and cottonseed oil which are unsaturated into solid fats which are of a saturated nature.

Question 13.

1. How are carboxylic acids different from mineral acids from an ionization point of view?
2. Describe an activity to show how ethanoic acid reacts with sodium carbonate. Name the gas evolved. How can it be tested?
3. State the principle on which the cleansing action of soap is based.

Answer:

Carboxylic acids (organic acids) are less ionized in solution as compared to mineral acids (HCl, HNO₃, H₂SO_4, etc.) Due to this reason, these are weaker acids than the mineral acids.

Take a small volume of ethanoic acid in a tube. Add a few drops ofsodium carbonate (Na₂CO₃) a solution prepared in water to the tube.

A colorless gas with brisk effervescence will evolve. When the gas is passed through lime water, it will become milky

⇒ \(\mathrm{Na}_2 \mathrm{CO}_3(a q)+2 \mathrm{CH}_3 \mathrm{COOH}(a q) \longrightarrow 2 \mathrm{CH}_3 \mathrm{COONa}(a q)+\mathrm{H}_2 \mathrm{O}(l)+\mathrm{CO}_2(g)\)

⇒  \(\underset{\text { Lime water }}{\mathrm{Ca}(\mathrm{OH})_2(a q)}+\mathrm{CO}_2(\mathrm{~g}) \longrightarrow \underset{\text { (Milky) }}{\mathrm{CaCO}_3(s)+\mathrm{H}_2 \mathrm{O}(l)}\)

The cleaning action of soap is based on its tendency to act as a bridge between water and oil drops containing dirt particles. As a result, oil and water get mixed. They form a stable emulsion also called micelle. This helps in removing oil drops containing dirt particles from clothes. The clothes become clean.

Question 14. Complete the following chemical reactions and write the chemical name ofthe products obtained.

1. CH₂ = CH₂ +HO

2. CHCOOH + NaOH

3.  CH₂CHOH → (H₂SO₄)

4. HCOOH + Na

5. C₂H₅OH → (AlK. KMnO₄)

Answer:

1. \(\mathrm{CH}_2=\mathrm{CH}_2+\mathrm{H}_2 \mathrm{O} \longrightarrow \mathrm{C}_2 \mathrm{H}_5 \mathrm{OH} \text { (Ethanol) }\)

2. \(\mathrm{CH}_3 \mathrm{COOH}+\mathrm{NaOH} \longrightarrow \underset{{\text { Sodium ethanoate }}}{\mathrm{CH}_3 \mathrm{COONa}}+\mathrm{H}_2 \mathrm{O}\)

3.

4. HCOOH + Na → HCOONa (Sodiumacid) + H₂

5.

Question 15.

1. Explain with the help of chemical equation for the following properties of carbon compounds:

1. Addition reaction
2. Substitution reaction

2. Differentiate between vegetable oils and animal fats.

3. What is meant by hydrogenation?

Answer:

1.

1. Addition reaction:  Unsaturated hydrocarbons add hydrogen in the presence of catalysts such as palladium or nickel.

2. Substitution reaction:  One type of atom or group of atoms takes the place of hydrogen.

CH₄ + Cl₂ →CH₃Cl + HCl (in the presence of sunlight)

2. Vegetable oils are unsaturated fatty acids and animal fats are saturated.

3. Adding hydrogen to unsaturated fatty acids.

Question 16.

1. Differentiate between saturated and unsaturated hydrocarbons. Write any two points of difference.

2. Why are carbon compounds:

1. Poor conductors of electricity?
2. Have low melting and boiling points?

3. Name the simplest hydrocarbon and write its formula

Answer:

1. 

2. Most carbon compounds are poor conductors of electricity as they do not ionize. Low melting and boiling points as the intermolecular force of attraction is very low.

3. Simplest hydrocarbon -Methane-CH₄

Question 17. Why is the conversion of ethanol to ethanoic acid an oxidation reaction?
Answer:

The conversion of ethanol to ethanoic acid is an oxidation reaction because oxygen is added to it during this conversion.

A mixture of oxygen and ethyne is burnt for welding. Can you tell why a mixture of ethyne and air is not used?

Ethyne with oxygen gives enough heat that be used for welding whereas if it is burnt in air, sufficient oxygen is not available and it burns with u sooty flame which does not give enough heat to melt metals for welding.

Question 18. People use a variety of methods to wash clothes. Usually after adding the soap, they ‘beat’ the clothes on a stone, or beat it with a paddle, scrub with a brush, or the mixture in a washing machine. Why is agitation necessary to get clean clothes?
Answer:

The molecules of soap are sodium or potassium salts of long-chain carboxylic acids. The ionic end of soap dissolves in water while the hydrocarbon chain gets attached to oily dirt on the clothes.

Thus, molecules called micelles are formed. When the cloth is agitated by different means, the micelles containing oily or greasy dirt particles get removed from the surface of the dirty cloth and go into the water, and the clothes get cleaned.

Question 19. How would you distinguish experimentally between an alcohol and a carboxylic acid?
Answer:

The distinction between alcohol and carboxylic acid can be made as follows:

Question 20. Explain the nature of the covalent bond using the bond formation in CH₃Cl.
Answer:

Covalent is formed by sharing ofelectrons so that combining atoms complete their outermost shell. In CH₃Cl, this happens as:

Three hydrogen atoms complete (K = 1 +1 = 2) their shells by sharing three electrons (one electron each) of carbon atoms. Chlorine completes its outer shell (L = 7 + 1 = 8) by sharing one out of seven electrons with one electron of a carbon atom.

Thus, the carbon atom shares all its four electrons with three hydrogen atoms and one chlorine atom and completes its outer shell (L = 4 + 3 + 1 = 8). 5.

Question 21. Draw the electron dot structures for

1. Ethanoic acid
2. H₂S
3. Propanone
4. F₂

Answer:

Question 22. Why does micelle formation take place when soap is added to water? Will a micelle be formed in other solvents such as ethanol?
Answer:

Soaps are sodium or potassium salts of long-chain carboxylic acids. The acid end of soap dissolves in water while the carbon chain dissolves in oil. When soap is added to the water, the hydrophilic end (acid end) will align along the surface of the water and the hydrophobic tail (carbon chain) remains out of water.

The cluster of molecules in which the hydrophobic tail is in the interior of the cluster and the ionic ends are on the surface of the cluster is called a micelle. The soap micelles thus help in dissolve the dirt in water and we can wash our clothes clean. No micelle will be formed in other solvents such as ethanol.

Question 23. Give a test that can be used to differentiate chemically between butter and cooking oil.
Answer:

Cooking oil is unsaturated hydrocarbon whereas butter is saturated hydrocarbon. We know that the brown color of bromine disappears when a drop of bromine is added to an unsaturated compound whereas there is no reaction between saturated hydrocarbons and bromine.

Thus, when a drop of bromine is added to cooking oil, its color disappears whereas there is no color change when a drop of bromine is added to butter.

Question 24. Explain the mechanism ofthe cleaning action of soaps.
Answer:

Dirt is generally absorbed in the clothes as an oily material. It cannot be removed with water because it does not mix well with water. But when a cloth with dirt is soaked in soap solution, the dirt and grease attach themselves to the hydrocarbon component of the soap molecule.

The —COONa part of the soap which is attached to the water molecules pulls the hydrocarbon part along with dirt away from the surface of the cloth, thus washing it clean.

Question 25. What is meant by a homologous series of carbon compounds? Write the general formula of

1. Alkene,
2. Alkynes

Draw the structures ofthe first member ofeach series to show the bonding between the two carbon atoms.

Answer:

A homologous series is called a series of organic compounds in which the same functional group substitutes for hydrogen in a carbon chain.

All consecutive members of this series differ by CH₂ unit.

Physical properties show gradation but chemical properties are the same.

The general formula of three compounds A, B, and C is CnH₂n. B has the highest boiling point and C has the lowest boiling point.

Mention the type of compounds A, B, and C.

Question 26. What is a homologous series? Explain with an example.
Answer:

A homologous series is a group of compounds that contain the same functional group but different chain lengths. Thus, these have the same chemical properties but different physical properties.

Two adjacent members ofa homologous scenes differ by a CH₂ unit. Examples CH₃OH, C₂H₅OH, C₃H₇OH, C₄ H₉ OH and C₂H₄, C₃H₆, C₄H₈, C₅H₁₀ two same homologous series respectively.

Question 27. How do diamond and graphite differ in their structures? Is there any effect of structures on the nature of these?
Answer:

1. Diamond and graphite are the two crystalline allotropic forms of carbon.
2. But they differ in their structures. In diamond, all the four valence electrons of carbon atoms are involved.
3. In the covalent bond formation with the electrons of neighboring carbon atoms In graphite, only three electrons participate in the bond formation while the fourth electron is free.
4. Diamond without nny free electrons is a poor conductor of electricity while e with free electrons available is a good conductor.

Question 28. An organic compound ‘X’ has the molecular formula CJi40. It has a pleasant smell. It does not turn blue litmus red; nor does it give any effervescence with sodium hydrogen carbonate solution. Predict the compound. Give its structural formula as well as the IUPAC name.
Answer:

Two different structural formulae are possible for the compound X’ with molecular formula C₂H₄O₂. These are known as functional isomers and may be written as:

StructureI is that of a carboxylic acid, ethanoic acid. Since the compound X’ does not turn blue litmus red and also does not give effervescence with NaHCO₃ solution, it cannot be an acid. As the compound has a pleasant smell, it seems to be an ester with structure 2. Please note that the esters have a pleasant smell. The IUPAC name of the compound is methylmethanoate.

Question 29.

1. Take about 3 mL of ethanol in a test tube and warm it gently in a water bath.
2. Add a 5% solution of alkaline potassium permanganate drop to the solution.
3. What happens to the color of KMnO₄ initially and then in excess? Give reason. Name the product of this reaction.

Answer:

The purple color of alkaline potassium permanganate solution, also known as Baeyer’s reagent gets initially discharged. On adding the reagent in excess, the purple color persists.

Baeyer’s reagent is an oxidizing agent. It provides oxygen to oxidize ethanol to ethanoic acid. Once the oxidation is complete, the further addition ofBaeyer’s reagent imparts the purple color to the solution.

Question 30.

1. Hydrocarbons generally act as fuels. How will you account for this?
2. Why is petrol regarded as a better fuel than kerosene?

Answer:

All hydrocarbons contain carbon and hydrogen. Both these elements are easily oxidized by oxygen to form carbon dioxide and water respectively. These reactions are highly exothermic and are accompanied by the release of a large amount of heat energy. That is why hydrocarbons generally act as fuels.

In petrol, the combustion of hydrocarbons present is complete and they bum with blue flame. However, in kerosene, the combustion is not complete. It burns with smoky flame accompanied by the release of unburnt carbon atoms. Therefore, petrol is regarded as a better fuel than kerosene.

Question 31. Draw the electron dot structure of ethyne and also draw its structural formula.
Answer:

The molecular formula of ethyne is C₂H₂.

Electronic configuration of C = 2, 4 (valence]electrons = 4)

Electronic configuration of H =1 (valence electrons = 1)

The electronic dot structure is

The structural formula is H — C≡ C—H (Ethyne)

Question 32. A salt X is formed and a gas is evolved when ethanoic acid reacts with sodium hydrogen carbonate. Name the salt X and the gas evolved. Describe an activity and draw the diagram ofthe apparatus to prove that the evolved gas is the one that you have named. Also, write the chemical equation ofthe reaction involved.
Answer:

CH₃COOH+NaHCO₃→ CH₃COONa +H₂O+CO₂

X is sodium ethanoate V

The gas evolved is carbon dioxide

Lime water will turn milky, a characteristic property of CO₂ gas.

Question 33.

1. What are hydrocarbons? Give examples.
2. Give the structural differences between saturated and unsaturated hydrocarbons with two examples each.
3. What is a functional group? Give examples of our different functional groups.

Answer:

1. Compounds of carbon and hydrogen are called hydrocarbons.

Examples: Methane, ethane, etc.

2. Saturated hydrocarbons contain carbon-carbon single bonds. Unsaturated hydrocarbons contain at least one carbon-carbon double or triple bond

3. Functional group:

An atom or a group of atoms joined in a specific manner that is responsible for the characteristic chemical properties of the organic compounds.

Examples are the hydroxyl group (—OH), aldehyde group (—CHO), carboxylic group (—COOH), etc.

Question 34. Name the reaction which is commonly used in the conversion of vegetable oils to fats. Explain the reaction involved in detail.
Answer:

Hydrogenation reaction:

Where R is the alkyl group.

Industrial use:

Vegetable oil + H₂ → (Ni,473K) → Vanaspati ghee

Question 35.

1. Write the formula and draw the electron dot structure of carbon tetrachloride.
   
2. What is saponification? Write the reaction involved in this process.
   

Answer:

1. Carbon tetrachloride

2. Saponification is the process of converting esters into salts of carboxylic acids and ethanols by treating them with a base.

CH₃COOC₂H₆ →( NaOH) →  CH₃COONa + C₂H₅OH

Question 36. Esters are sweet-smelling substances and are used in making perfumes. Suggest some activity and the reaction involved in the preparation of an ester with a well-labeled diagram.

Answer:

Activity

• Take 1 mL ethanol (absolute alcohol), 1 mL glacial acetic acid, and a few drops of concentrated sulphuric acid in a test tube.
• Warm in a water bath at about 60°C for at least 15 minutes as shown in the figure (It should not be heated directly on flame as the vapors of ethanol catch fire)
• Pour into a beaker containing 20-50 mL of water and smell the resulting mixture.

Question 37. A compound C(molecularformula, reacts with Na-metal to form a compound R and evolves a gas that burns with a pop sound. Compound C on treatment with alcohol A in the presence of an acid forms a sweet-smelling compound S (molecular formula)

In addition to NaOH to C, it also gives R and water. S on treatment with NaOH solution gives back R and A. Identify C, R, A, and S and write down the reactions involved.

Answer:

C — Ethanoic acid

R— Sodium salt of ethanoic acid (sodium acetate) and gas evolved is hydrogen.

A — Methanol

S — Ester (Methyl acetate)

1. 2CH₃COOH (C) + 2Na → 2CH₃COONa (R) + H₂

2. CH₃COOH  (C) + CH₃OH (A) →(Conc.H₂SO₄)   CH₃COOCH₃ (S) + H₂O

3. CH₃COOH₃ + NaOH → CH₃COONa (R) +  H₂O

4. CH₃COOCH₃ + NaOH→ CH₃COONa(R) +  CH₃ OH (A)

Question 38. Look at the figure and answer the following questions

1. What change would you observe in the calcium hydroxide solution taken in tube B?
2. Write the reaction involved in test tubes A and B respectively.
3. If ethanol is given instead of ethanoic acid, would you expect the same change?
4. How can a solution of lime water be prepared in the laboratory?

Answer:

1. It will turn milky

2. 2CH₃COOH + Na₂CO₃→ 2CH₃COONa + H₂O + CO₂ (Test tube A)

Ca(OH)₂ + CO₂→CaCO₃ + H₂O(Test tube B)

With excess CO₂, milkiness disappears.

CaCO₃ + H₂O + CO₂→ Ca(HCO₃)₂

3. As C₂H₅OH and Na₂CO₃ do not react, a similar change is not expected.

4. The lime water is prepared by dissolving calcium oxide in water and decanting the supernatant liquid.

Question 39. How would you bring about the following conversions? Name the process and write the reaction involved.

1. Ethanol to ethene
2. Propanol to propanoic acid

Write the reaction.

Answer:

1. Dehydration:

2. Oxidation reaction:

Question 40. Draw the possible isomers ofthe compound with molecular formula C₃H₆O and also give their electron dot structures
Answer:

1. CH₃-C=O – CH₃ (Propanone):

2. CH₃CH₂CHO (Propanal):

Question 41. Explain the given reactions with examples:

1. Hydrogenation reaction
2. Oxidation reaction
3. Substitution reaction
4. Saponification reaction
5. Combustion reaction

Answer:

1. Hydrogenation reaction:

Unsaturated hydrocarbons add hydrogen in the presence of a nickel catalyst to give saturated hydrocarbons.

2. Oxidation reaction:

Ethanol is oxidized to ethanoic acid in the presence of alkaline KMnO₄ on heating.

3. Substitution reaction:

In the presence of sunlight, chlorine is added to hydrocarbons.

4. Saponification reaction:

⇒ \(\underset{\text { Ester }}{\mathrm{CH}_3 \mathrm{COOC}_2 \mathrm{H}_5}+\mathrm{NaOH} \longrightarrow \underset{\text { Sodium acetate }}{\mathrm{CH}_3-\mathrm{COO}-\mathrm{Na}}+\underset{\text { Ethanol }}{\mathrm{C}_2 \mathrm{H}_5 \mathrm{OH}}\)

5. Combustion reaction:

Most carbon compounds release n large amount of heat and light on burning.

⇒ \(\mathrm{CH}_4+2 \mathrm{O}_2 \longrightarrow \mathrm{CO}_2+2 \mathrm{H}_2 \mathrm{O}+\text { Heat and ligh }\)

Question 42. An organic compound A on heating with concentrated H₂SO₄ forms a compound B which on the addition of one mole of hydrogen in the presence of Ni forms compound C. One mole of compound C on combustion forms two moles of CO₂ and 3 moles of H₂O. Identify the compounds A, B, and C and write the chemical equations ofthe reactions involved.
Answer:

Since compound C gives 2 moles of CO₂ and 3 moles of H₂O, it shows that it has the molecular formula C₂H₆ (Ethane). C is obtained by adding one mole of hydrogen to compound B so the molecular formula of B should be C₂H₄ (Ethene).

Compound B is obtained by heating compound A with concentrated H₂O₄ which shows it to be an alcohol. So compound A could be C₂H₅OH (Ethanol).

Question 43. Study the variation in the atomic radii of the first group elements given below and arrange them in increasing order.

1. Name the elements that have the smallest and the largest atoms

2. How does the atomic size vary as you go down a group?
Answer:

1. The smallest atom—is lithium and the largest atom is cesium

Question 44. How would you bring about the following conversions? Name the process and write the reaction involved.

1. Ethanol to ethene
2. Propanol to propanoic acid

Answer:

1. By the dehydration of ethanol in the presence of concentrated H₂SO₄

2. By the dehydration of propanol in the presence of alkaline KMnO₄

Question 45. Write an activity to show the acidic nature ofethanol. Give the chemical equation of the reaction taking place.
Answer:

Take ethanol in a test tube and drop a small piece ofsodium about the size of a grain of rice into it. The reaction evolves a colorless gas which is hydrogen.

Hydrogen gas can be tested by bringing a burning splinter/match stick near the mouth of the test tube, it burns with the popping sound. This activity proves that ethanol like other acids releases H gas.

2CH₃CH₂OH + 2Na → 2CH₃CH₂ONa + H₂

Question 46. A student reports to police about the illegal blending of alcohol near his school. He also knew about denatured alcohol.

1. What is denatured alcohol?
2. What would happen if a person consumes denatured alcohol?
3. What value is reflected by a student who reported the matter to the police?

Answer:

1. Denatured alcohol is ethanol when added with poisonous methanol or CuSO₄.
2. On drinking denatured alcohol, a person may die.
3. Value reflected is in society’s decorum of law and order.

Question 47. Mrs. Anju Pandey observed that her cooking utensils are becoming black and the flame other gas stove is yellowish. She complained about it in the gas company and got thegas stove repaired. Answer the following questions based on the above situation.

1. What can be the reason for this sooty flame?
2. How is this problem harmful to our environment?
3. What steps should be taken to stop this process?
4. What values are promoted by Mrs. Pandey?

Answer:

• The inlets for air in the stove get blocked which leads to a yellow flame.
• This problem is harmful to our environment as incomplete combustion results in the formation of oxides which are major pollutants of our environment.
• To prevent this situation, gas or stove burners should be cleaned from time to time.
• Prudence, careful observations, and decision-making.

Question 48. Ethanol, commonly known as alcohol is an excellent solvent, is used in medicines, and is an important chemical compound involved in the synthesis of many chemical compounds.

However, despite its benefits to man, its impact on social behavior has always been questioned. It is considered as a curse in the lives of those who are addicted to alcohol—

‘Alcoholic people are not only lowering their metabolism but anger and rude behavior are also some of its ill effects.

Answer the following questions based on the above information:

1. Comment on the statement—‘Should the production of alcohol be banned?’ Give three valid reasons to justify.
2. As a student, what initiative would you take in the common concern of ‘ Save Life, Do Not Drink’? Give two suggestions.

Answer:

1.

In favor of a negative response:

1. Regulate production and supply.
2. It is used in so many ways for medicines and ornamentation.

In favor of a positive response:

• Cause of death of many people.
• Many adolescents get affected out of it and become addicts, which affects their physical as well as mental health.

2. Initiatives:

1. Drive to spread awareness.
2. Skit/street plays/drama.
3. Organise exhibitions.

Question 49. The element carbon is known to have the unique ability to form bonds with other similar atoms of other elements. The carbon-carbon bond is also known to be very strong and hence stable.

Answer the following questions based on the above information:

1. Name the chemical bond formed between carbon-carbon atoms. How is this bond formed?
2. Which two values are reflected like carbon resulting in its ability to form a maximum number of compounds’?
3. How can these values help strengthen relationships in a family, organization, or even people ofa nation?

Answer:

1. Covalent bond: Sharing of bonds
2. Ability to share, nature to share
3. Sharing of one’s possessions, jobs, and resources with others enables an individual organization or even a society to live happily and comfortably.

Question 50. Write the structural formulae of all the isomers of hexane.
Answer:

Structural formulae of all the isomers of hexane:

Question 51. What is the role of metal or reagents written on arrows in the given chemical reactions?

Answer:

1. Ni acts as a catalyst.
2. Concentrated sulphuric acid acts as a dehydrating agent.
3. Alkaline KMnO₄ acts as an oxidizing agent.

Question 52. Why should we prefer vegetable oils over animal fats for cooking food? Give a balanced chemical equation ofthe reaction for hydrogenation of vegetable oils. Name, the catalysts in this reaction.
Answer:

Animal fats are saturated fatty acids that are harmful to health.

Catalyst: Palladium or Nickel

Question 53. Convert CH₄ into CCl₄ by substituting hydrogen atom with chlorine atom in successive reactions. Why this reaction is referred to as a substitution reaction?
Answer:

CH₄+ Cl₂ →(Sunlight ) → CH₃CI + HCl

CH₃CI + Cl₂ →CH₂Cl₂ + HCl

CH₂Cl₂ + Cl₂ →CCl + HCl

CHCl₃ + Cl₂ → CCl + HCl

Replace the hydrogen atom with a heteroatom (Cl).

Question 54. The organic compound ‘A’ is an essential constituent of wine and beer. Oxidation of ‘A’ yields an organic acid ‘B’ which is present in vinegar. Name the compounds ‘A’ and ‘B’ and write their structural formula. What happens when”A’ and ‘B” react in the presence of an acid catalyst? Write the chemical equation for the reaction.
Answer:

The available information suggests that the compound ‘A’ is ethanol and the compound B formed by the oxidation of‘A’ is ethanoic acid.

Their structural formula is are 

Ethanol (A)

Ethanoic Acid (B)

When ‘A’ and ‘B’ react the presence ofan acid cone. H₂SO₄, the compound is ethyl ethanoate ester with a pleasant smell.

NCERT Solutions For Class 10 Science Chapter 6 Life Processes

Question 1.

1. Describe the mechanism of breathing in human beings.
2. 1. Under normal conditions, what is the rate of breathing per minute?
   2. Why does the rate of breathing increase by 20 to 25 times during vigorous exercise?

Answer:

1. Mechanism of breathing in Humans: Breathing is a complex mechanical process involving muscular movement that alters the volume of the thoracic cavity and thereby that of the lung.

• Breathing occurs involuntarily but its rate is controlled by the respiratory centre of the brain.
• The space of the thoracic cavity increases or decreases by outward and inward movements of the ribs caused by external intercostal and internal intercostal muscles.
• This action is also assisted by the contraction and expansion of the diaphragm. The floor of the thoracic cavity is completely closed by the diaphragm. It is a thin muscular septum separating the abdominal and thoracic cavities.
• Inspiration or inhalation is concerned with the taking in of atmospheric air or oxygen into the thoracic cavity.
• Expiration or exhalation is concerned with the expelling of carbon dioxide from the lungs. It takes place when the volume of the thoracic cavity decreases and the pressure of the contained air in the thoracic cavity increases.

2. (1) Under normal conditions, the rate of breathing is 12 to 18 times per minute.

(2) The rate of breathing during vigorous exercise increases by about 20 to 25 times per minute. This is because, during vigorous exercise, the demand for oxygen increases. Breathing occurs involuntarily but its rate is controlled by the respiratory centre of the brain.

Read and Learn More Class 10 Science Solutions

Question 2.

1. Draw a diagram of the human alimentary canal and label it: Oesophagus, Gall bladder, Liver and Pancreas.
2. Explain the statement, ‘Bile does not contain any enzyme but it is essential for digestion’.

Answer:

1. Bile does not contain any enzyme but it is essential for digestion because:
   1. It maintains an alkaline medium for another enzyme to work.
   2. It helps in the emulsification of fats i.e., converts them into small globules.

Question 3.

1. Write two differences between autotrophic nutrition and heterotrophic nutrition.
2. Draw a diagram showing a cross-section of a leaf and label it:
   Phloem, Xylem, Vascular bundle, Lamina.

Answer:

Question 4.

1. State the reason for the following:
   1. Herbivores need a longer small intestine while carnivores have shorter small intestine.
   2. The lungs are designed in human beings to maximise the area for the exchange of gases.
2. The rate of breathing in aquatic organisms is much faster than that seen in terrestrial organisms.

Answer:

1. 1. Herbivores which eat grass have a longer small intestine for the digestion of cellulose because cellulose takes much time to be digested and it remains for a longer time inside the small intestine. Carnivores which eat meat have a shorter small intestine because meat is easily digestible. Hence, they do not need a longer smaller intestine.
   2. Inside the lungs, the trachea divides and redivides to form numerous fine tubes, the bronchi and bronchioles which finally end in inflated balloon-like structures called alveoli. Alveoli have an extensive network of blood vessels in their thin walls. Hence, they provide a large surface area for the diffusion of gases across their walls.
2. The amount of dissolved oxygen is fairly low compared to oxygen in air. The fishes take in water through their mouths and force it past the gills where the dissolved oxygen is taken up by blood.

Question 5.

1. Draw the structure of a nephron and label the following on it: Glomerulus, Bowman’s capsule, Renal artery, and Collecting duct.
2. What happens to glucose that enters the nephron along with filtrate?

Answer:

Glucose that enters the nephron along with the filtrate after passing through the glomerulus, passes from the tubule of the nephron where it is selectively reabsorbed and sent back to blood.

Question 6.

1. Draw a sectional view of the human heart and label it the Aorta, Pulmonary arteries, Vena cava, and Left ventricle.
2. Why is double circulation of blood necessary in human beings?

Answer:

Double circulation of blood is necessary to:

1. Separate deoxygenated blood from oxygenated blood.
2. Meet high energy and oxygen demands.
3. Maintain constant body temperature.

Question 7.

1. Draw a labelled diagram of the respiratory system of human beings with a diaphragm at the end of expiration.
2. List four conditions required for efficient gas exchange in an organism.

Answer:

The conditions required for efficient gas exchange in an organism are that the membrane should be extensive, thin, highly vascularised and easily permeable to oxygen and carbon dioxide.

Question 8.

1. Draw a schematic representation of the transport and exchange of oxygen and carbon dioxide during the transportation of blood in human beings and label it: Lung capillaries, Pulmonary artery to lungs, Aorta to body, and Pulmonary veins from lungs.
2. What is the advantage of separate channels in mammals and birds for oxygenated and deoxygenated blood?

Answer:

It is necessary to separate oxygenated and deoxygenated blood in mammals and birds because they need high energy and a large amount of oxygen. The separation of oxygenated and deoxygenated blood provides high oxygen supply to the organs.

Question 9.

1. Draw a diagram to show the nutrition in Amoeba and label the parts used for this purpose. Mention any other purpose served by this part other than nutrition.
2. Name the glands associated with the digestion of starch in the human digestive tract and mention their role.
3. How is the required pH maintained in the stomach and small intestine?

Answer:

Pseudopodia serves the purpose of locomotion apart from nutrition.

The salivary gland is associated with the digestion of starch in the human digestive tract. It secretes saliva with the help of the enzyme salivary amylase which converts starch into maltose (sugar).

Gastric glands present on the walls of the stomach release HCl acid. HCl creates an acidic medium, which facilitates the action of the enzyme pepsin. Bile juice from live makes the food alkaline in the small intestine for the pancreatic enzymes to act.

Question 10.

1. Leaves of a healthy potted plant were coated with vaseline to block the stomata. Will this plant remain healthy for long? State three reasons for your answer.
2. State any two differences between autotrophic nutrition and heterotrophic nutrition.

Answer:

1. No, this plant will not remain healthy for long. The plant will begin to die because
   1. Gaseous exchange will not take place.
   2. No absorption of CO₂, hence no photosynthesis.
   3. Transpiration will not occur; hence no transport of water.
2. Differences

Question 11. Explain the process of nutrition in Amoeba.
Answer:

Amoeba is a unicellular animal which follows the holozoic mode of nutrition. The process of obtaining food by Amoeba is called phagocytosis.

The various steps involved in phagocytosis are:

1. Ingestion: Amoeba ingests food particles by forming temporary finger-like projections called pseudopodia around it. The food is engulfed forming a food vacuole.
2. Digestion: Inside the food vacuole, complex substances are broken down into simpler ones by digestive enzymes.
3. Absorption: The digested food present in the food vacuole diffuses into the cytoplasm. After this, the food vacuole disappears.
4. Assimilation: Food absorbed is used by Amoeba for various processes.
5. Egestion: The remaining undigested material moves to the surface of the cell, the cell membrane ruptures at any place and undigested food is thrown out of the body.

Question 12. Describe the alimentary canal of man.
Answer:

Alimentary canal of man: It measures about 8 to 10 metres in length and extends from mouth to anus. It has the following parts.

Mouth: It consists of the oral cavity, through which food is ingested. It contains teeth, tongue and three pairs of salivary glands.

Pharynx: The oral cavity opens into the pharynx. The swallowing mechanism guides the masticated food through the pharynx into a tube, called oesophagus.

Oesophagus: It is a muscular, tubular part of the alimentary canal. The muscular movement called peristalsis carries the food down to the stomach.

Stomach: It is a J-shaped sac-like muscular structure that serves as a storehouse of food. It is a large organ which expands when food enters it. The muscular wall helps in mixing food thoroughly with more digestive juices.

Small Intestine: It is about 6 metres in length and has three divisions, i.e., duodenum (the first part is C-shaped, and begins from the pyloric stomach), jejunum and ileum.

Large Intestine: The ileum passes into the large intestine, which can be divided into two parts anterior colon and posterior rectum. The terminal part of the rectum is called the anal canal. It opens through the anus, guarded by sphincter muscles. It allows the faecal matter to be egested out.

Question 13. Explain the process of breathing in man.
Answer:

Breathing in humans involves the following steps:

1. Inspiration: When we breathe in, the muscles between ribs contract causing the rib cage to move upward and outward, and the diaphragm contracts and moves downward. As the chest cavity becomes large, the air is sucked in from outside into the lungs, the lungs get filled up with air and expand.
2. Gaseous exchange: Haemoglobin in RBCs binds with oxygen and carries it along the body with blood. As blood passes through the tissue of the body, the oxygen from blood diffuses into cell whereas CO2 produced during respiration diffuses into the blood and is carried to the lung.
3. Expiration: When we breathe out, the muscles between the ribs relax causing the rib cage to move downward and inward and the diaphragm relaxes and moves upward. As the chest cavity becomes smaller, air is pushed out from the lungs.

Question 14. Explain the importance of soil for plant growth.
Answer:

Soil is important for plant growth due to following reasons:

1. Soil provides a base on which terrestrial and aquatic plants grow.
2. Soil is a reservoir of water and minerals, essential for all metabolic activities of a plant.
3. The roots of the plant take oxygen for the process of respiration.
4. Some plants also form symbiotic associations with microbes present in the soil to absorb minerals.

Question 15. Draw the diagram of the alimentary canal of man and label the following parts. Mouth, Oesophagus, Stomach, Intestine.
Answer:

The diagram of the alimentary canal of man and its parts are shown as follows:

Question 16. How do carbohydrates, proteins and fats get digested in human beings?
Answer:

Digestion of carbohydrates starts from:

Buccal cavity: The food receives saliva in the buccal cavity, which contains salivary amylase. It breaks down starch into simple (glucose) sugar.

In small intestine

Pancreatic juice contains pancreatic amylase, which acts in further breakdown of starch.

Intestinal juice contains the following

Intestinal amylase hydrolyses the remaining starch and glycogen.

Digestion of proteins starts

In the stomach: An inactive form of pepsin is secreted, known as pepsinogen, which in the presence of HCl forms pepsin and digests protein.

Pepsinogen + HCl → Pepsin

In small intestine

1. Pancreatic juice secretes trypsinogen, chymotripsinogen (inactive form of trypsin) which on activation forms trypsin and digests protein.
2. Intestinal juice

Digestion of Fats begins

In small intestine

Bile emulsifies fats into smaller droplets

Pancreatic juice present in the small intestine acts as follows:

Intestinal juice acts as follows:

Question 17. Explain the mechanism of photosynthesis.
Answer:

The process by which green plants make their own food in the form of glucose from CO₂ and HO by using sunlight energy in the presence of chlorophyll, is called photosynthesis. Oxygen gas is released during photosynthesis.

It occurs in green plants by the following steps:

1. Sunlight energy is absorbed by chlorophyll.
2. This energy is converted into chemical energy. C₆H₁₂O₆+6O₂
3. Water molecule is split into hydrogen and oxygen molecules. The oxygen gas produced as a by-product goes into the air.
4. The hydrogen released during the above reaction is utilised for reduction of CO₂ from carbohydrates by utilising the chemical energy.
5. The extra glucose is stored as starch in the leaves of the plant.

Questionb 18. Explain the three pathways of breakdown in living organisms.
Answer:

In the process of respiration, the first step is the breakdown of glucose, a 6-carbon molecule breaks into 2 molecules of a 3-carbon molecule called pyruvate. This process takes place in the cytoplasm.

The subsequent breakdown pathway depends on the absence or presence of oxygen as follows:

Aerobic respiration: It takes place in the mitochondria in the presence of oxygen. Pyruvic acid is converted into carbon dioxide and water, thus releasing a lot of energy.

Anaerobic respiration: It takes place in the cytoplasm in the absence of oxygen. Pyruvic acid is converted either into CO₂ and ethanol (inthe  case of microbes, i.e., fermentation in yeast) or into lactic acid (in the case of muscle cells during sudden. activity in humans.)

Question 19. Describe the flow of blood through the heart of human beings.
Answer:

Flow of blood through the human heart: Oxygen-rich blood from the lungs comes to the thin-walled upper chamber of the heart on the left, the left atrium.

• The left atrium relaxes when it is collecting this blood. It then contracts, to enter the next chamber, the left ventricle, which expands, so that the blood is transferred to it. When the muscular left ventricle contracts the blood is pumped out to the body.
• Deoxygenated blood reaches from the body to the upper chamber on the right, the right. atrium, and it expands. As the right atrium contracts, the corresponding lower chamber, the right ventricle, dilates.
• This transfers blood to the right ventricle, which in turn pumps it to the lungs for oxygenation. Since ventricles have to pump blood into various organs, they have thicker muscular walls than the atria do.

The whole process is repeated continuously. The blood circulatory system in humans is an example of double circulation since the blood travels twice through the heart in one complete cycle.

1. The pathway of blood from the heart to the lungs and back to the heart is called pulmonary circulation.
2. The pathway of blood from the heart to the rest of the body and back to the heart is called systemic circulation.

These two together make a double circulatory system.

Question 20. Describe the process of urine formation in kidneys.
Answer:

Urine is formed in the kidneys in the nephron i.e., the structural and functional unit of the kidney. Blood at high pressure travels into these tubules by the tuft of blood capillaries called glomerulus.

The following steps are involved in the process:

1. Filtration: Blood enters the glomerulus through the afferent arterials, it passes under pressure that results in filtration of blood. Water and small molecules are forced out of glomerular capillary walls and Bowman’s capsule. Large molecules remain in the blood of the glomerulus.
2. Selective reabsorption: Some molecules are selectively reabsorbed into the blood. The glomerular filtrate flows through the proximal convicted tubule, U-shaped Henle’s loop and distal convoluted tubule. The useful substances present such as glucose, amino acids and salts are reabsorbed by a process which requires energy.
3. Tubular secretion: Some nitrogenous waste products like creatinine and some other substances like K+ are removed from the blood by DCT and are added to the urine. The urine formed is collected in the urinary bladder.

NCERT Solutions For Class 10 Science Chapter 7 Control and Coordination

Question 1. What is geotropism? Describe an experiment to demonstrate positive and negative geotropism.
Answer:

The upward growth of shoots and the downward growth of roots in response to the pull of the earth or gravity is known as geotropism.

Experiment: Take a small healthy potted plant. Make a hole at the bottom of the pot. Tilt the pot so that it rests on its edge so that the plant becomes in a horizontal position. Place the tilted potted plant in a safe space.

• Water the plant from time to time. After some days, you will find the shoot growing upward, that is, away from the force of gravity showing negative geotropism, and the roots coming out of the bottom of the pot grow downward, that is, towards the force of gravity showing positive geotropism.
• (This upward growth of young shoots and downward growth of roots are seen due to the unilateral effect of gravity).

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Question 2. State the sequence of change that takes place in the human body when it prepares itself to protect itself from a scary or dangerous situation.
Answer:

1. Target organs or specific tissues on which it acts include the heart.
2. Under the influence of adrenaline, the heart beats faster to supply more oxygen to the heart muscles.
3. The blood supply to the digestive system and skin is reduced due to the contraction of muscles around small arteries in these organs This causes the diversion of the blood to skeletal muscles.
4. There is an increase in breathing rate. It happens because of the contraction of the diaphragm and rib muscles.
5. All these responses together enable the body to meet with the situation (emotional stress).
6. Thus, hormones secreted by the endocrine system act as a second way to control and coordinate in our body.

Question 3.

1. Name one organ each where growth hormone is synthesized in man and plant.
2. List the sequence of events that occur when a plant is exposed to unidirectional light, leading to the bending of a growing shoot. Also, name the hormone.

Answer:

1. The pituitary gland in men and shoot tip in plants.
2. Auxin diffuses towards the shady side and causes elongation of one side (shady side) resulting in bending. When light is coming from one side of the plant, auxin diffuses towards the shady side. This concentration stimulates the cells to grow longer on that side of the shoot which is away from the light and thus the shoot bends. The name of the hormone is Auxin.

Question 4.

1. Explain how auxins help in the bending of plant stems towards the light.
2. State the objective of the experiment, for which the experimental setup is shown in the given diagram.

Answer:

1. When a growing plant detects light, auxin synthesizes at the shoot tip to help the cells grow longer. When light comes from one side, auxin diffuses towards the shady side of the shoot. This concentration of auxin stimulates the cells to grow longer on the side of the shoot which is away from light and the plant appears to bend towards light.
2. The objective of the experiment is to show the phototropic movement of the plant.

Question 5. What is meant by reflex action? With the help of a labeled diagram trace the sequence of events that occur when we touch a hot object.
Answer:

Reflex action is defined as an unconscious, automatic, and involuntary response of the effector, i.e., muscle and gland to a stimulus which is monitored through the spinal cord.

A sequence of events when we touch a hot object are:

1. Receptor organ skin receives the stimulus and activates a sensory nerve impulse.
2. Sensory neuron carries the message in the form of sensory impulses to the spinal cord.
3. The spinal cord acts as a modulator. The neurons of the spinal cord transmit the sensory neural impulses to motor neurons.
4. The motor nerve conducts these impulses to the effector organ hand which responds by pulling back the hand away from the hot object.

Question 6. State the functions of plant hormones. Name four different types of plant hormones.
Answer:

Plant hormones help to coordinate growth, development, and responses in the environment. Four different types of plant hormones are Auxins, Gibberellins, Cytokinins, and Abscisic acid.

1. Auxins are the group of plant hormones synthesized at the shoot-tip of the plant body. These promote cell elongation, root formation, cell division, respiration, and other physiological processes like protein synthesis, water uptake, and protoplasmic permeability. Auxins also play an important role in the development of seedless fruits.
2. Gibberellins stimulate stem elongation, seed germination, and flowering. The maximum concentration of gibberellins is found in fruits and seeds.
3. Cytokinins are produced in dividing cells throughout the plant. In mature plants, cytokinins are produced in the root tips and are transported to the shoots. Cytokinins promote cell division and also help in breaking the dormancy of seeds and buds and regulate the phloem transport. Cytokinins delay the aging in leaves and promote the opening of stomata.
4. Abscisic acid is a growth inhibitor that reverses the growth-promoting effects of auxins and gibberellins. Its effects include wilting of leaves. It causes dormancy of seeds. It also promotes the closing of stomata.

Question 7.

1. Name the hormone which is released into the blood when its sugar level rises. Name the organ which produces this hormone and its effect on blood sugar levels. Also, mention the digestive enzymes secreted by this organ with one function of each.
2. Explain the need for Chemical communication in multicellular organisms.

Answer:

1. When the sugar level rises, the hormone insulin is released into the blood. Insulin is released in our body by the pancreas. When insulin is secreted in lower quantities by the pancreas, the blood sugar level of the concerned person increases. On the other hand, if the insulin is secreted in excess, the person suffers from low sugar in the blood.
2. Chemical communication is required in multicellular organisms to deal with emergency demands such as infection, trauma, dehydration, starvation, hemorrhage, extreme temperature, etc.

Question 8. A young boy met an accident while riding a bike. Patrolling police found the boy and brought him to a hospital for treatment. After the accident, the boy lost his memory completely. The left side of his body also suffered from paralysis.

1. What values were shown by police persons?
2. Which injured body part can cause paralysis?
3. What precautions should one take while riding a two-wheeler?

Answer:

1. The values shown by the police persons were truthful to duty and humanity.
2. Injury to the brain or spinal cord can cause paralysis.
3. Riders must wear helmets while riding a two-wheeler. One must drive at a controlled speed to avoid accidents.

Question 9. What is a reflex arc? Draw a neat labeled diagram of the components in a reflex arc. Why do impulses flow only in one direction in a reflex arc?
Answer:

The reflex arc is the pathway taken by the nerve impulses and responses in a reflex action, i.e., from the receptor organs like skin to the spinal cord and from the spinal cord to the effector organs like muscles.

Impulses flow only in one direction in a reflex arc, because each synapse in the reflex arc allows impulses to cross it in a single direction.

Question 10. With the help of a flow chart, highlight the various types of plant movements with suitable examples.
Answer:

Question 11.

1. Name the parts labeled A and B in the neuron drawn above.
2. Which part acquires the information in the neuron?
3. Through which part does the information travel?
4. In what form does this information travel?
5. Where is the impulse converted into a chemical signal for onward transmission?

Answer:

1. A- Dendrite B-Axon
2. The information in the neuron is acquired at the end of the dendrite tip.
3. The information travels from the dendrite to the cell body and then along the axon to its end.
4. The information travels in the form of an impulse.
5. The impulse is converted into a chemical signal at the end of the axon.

Function of thyroxine hormone:

It regulates carbohydrate, protein, and fat metabolism in the body to provide the best balance for growth.

The use of iodized salt is advisable because iodine is essential for the synthesis of thyroxin. In case of iodine deficiency in our diet, there is a possibility one can suffer from goiter, which is a disease of the swollen neck.

Question 12. Suggest six reflex actions of the body. Explain how the reflex arc is the same in all of them.
Answer:

1. Six reflex actions of the body are as follows:
2. When we see a speeding car moving towards us, we move aside.
3. We withdraw our hands from being pricked by a pin.
4. We withdraw our hands on touching a very hot substance.
5. We close our eyes to see the direct sun or extremely bright source of light.
6. We close our eyes on hear a loud noise.
7. We shiver on feeling cold.

The reflex arc in all the above cases is the same because in all the cases, the stimulus is received by sense organs Then this information is carried to the spinal cord through sensory nerves. Thus, information from the spinal cord is sent to the effectors such as muscles via motor neurons.

Question 13. Draw the structure of a neuron and explain its function.
Answer:

Neurons are the units that make up the nervous system. These are the structural and functional units of the nervous system. These carry messages over large distances in the body quickly.

A neuron (or nerve cell) has three components:

1. Cell body: It contains cytoplasm and nucleus.
2. Dendrites: These are shorter fibers on the body of neurons.
3. Axon: It is the longest fiber on the cell body of a neuron.

Question 14. What are the major parts of the brain? Mention the functions of different parts.
Answer:

Question 15. What constitutes the central and peripheral nervous systems? How are the components of the central nervous system protected?
Answer:

The central nervous system consists of the brain and spinal cord.

1. Brain: It is the main coordinating center in the body. It is lodged in the brain box or cranium which protects it. It is covered by membranes called meninges, which also help to protect it.
   • The space between the membranes and the brain is filled with cerebrospinal fluid which protects the brain from mechanical shock. The brain is broadly divided into three regions: fore-brain, mid-brain, and hind-brain.
2. Spinal cord: It is a long cylindrical structure. It begins from the medulla oblongata and extends downwards. It is enclosed in a bony cage called a Vertebral column that protects it.
   • It is also surrounded by meninges. It is concerned with spinal reflex actions and the conduction of nerve impulses to and from the brain.

Peripheral Nervous System (PNS)

It includes the following:

1. Cranial nerves have 12 pairs that emerge from the brain.
2. Spinal nerves 31 pairs that arise from the spinal cord and spread throughout the body.
3. Visceral nerves: They are a special kind of nerves that mostly arise from the spinal cord and are connected to the internal organs of the body. They carry both sensory and motor neurons. The PNS works according to our will.

Question 16. Mention one function for each of these hormones:

1. Thyroxin
2. Insulin
3. Adrenaline
4. Growth hormone
5. Testosterone.

Answer:

1. Thyroxin regulates carbohydrate, fat, and protein metabolism in the body to provide the best balance for growth.
2. Insulin regulates blood sugar levels.
3. Adrenaline increases heart rate and supply of blood to various organizers:
4. Growth hormone regulates growth and development.
5. Testosterone controls the changes in body features associated with puberty in males.

Question 17. Name various plant hormones. Also give their physiological effects on plant growth and development.
Answer:

Question 18. What are reflex actions? Give two examples. Explain a reflex arc.
Answer:

Reflex action is a rapid, automatic response to a stimulus that is not under the voluntary control of the brain i.e., it is an involuntary action. It is a simple form of behavior in which the same stimulus produces the same response every time, for example.,

1. If we unknowingly touch a hot plate, we immediately move our hand away from it.
2. A sharp thing like a nail touches our body.

Other examples are knee jerk, coughing, yawning, etc.

The pathway taken by nerve impulses in a reflex action is called the reflex arc. Reflex arcs have evolved in animals because the thinking process of the brain is not fast enough. However, even after complex neuron networks have come into existence, the reflex arc continues. to be more efficient for quick responses.

Question 19. The nervous and hormonal systems together perform the function of control and coordination in human beings. Justify the statement.
Answer:

The working together of various organs of human beings in a systematic, controlled, and efficient way to produce a proper response to various stimuli is known as coordination. In humans, the nervous and hormonal systems together perform this control and coordination.

• The nervous system consists of receptors that receive stimuli from the surrounding environment and send the message conveyed by them to the spinal cord and brain in the form of electrical impulses through the sensory nerves.
• The motor nerves then transmit the response to the ‘effector’. The effectors are mainly the muscles and glands of our body.
• Thus, endocrine glands secreting hormones are directly or indirectly controlled by the nervous system.
• Hence, control and coordination in humans (or animals) depend on two things for transmitting information i.e., chemical signals of hormones and nerve impulses.
• If they depend upon only nerve impulses through nerve cells, a limited range of tissues would be stimulated.

Question 20. How does chemical coordination take place in animals?
Answer:

Different endocrine glands secrete different hormones. These hormones are released into the blood which carries them to specific tissues or organs called target tissues or target orgAnswer: In the target tissues, the hormone triggers a particular biochemical or physiological activity.

Question 21. Why is the flow of signals in a synapse from the axonal end of one neuron to the dendritic end of another neuron, but not the reverse?
Answer:

When an electrical signal reaches the axonal end of a neuron, it releases a chemical substance. This chemical diffuses towards the dendrite end of the next neuron where it generates an electrical impulse or signal.

Hence, the electrical signal is converted into a chemical signal at the axonal end. Since these chemicals are absent at the dendrite end of the neuron the electrical signal cannot be converted into a chemical signal.

Heredity And Evolution Long Answer Questions

Question 1. The genotype of green-stemmed tomato plants is denoted as GG and that of purple-stemmed tomato plants as gg. When these two are crossed:

1. What colour of stem would you expect in their F, progeny?
2. Give the percentage of purple-stemmed plants if F, plants are self-pollinated.
3. In what ratio would you find the genotypes GG and Gg in the F2 progeny?

Answer:

1. Green (as G denote the tes dominant gene and is expressed in all plants of F₁ generation).
2. 25% in F₂ generation raised by self-pollinated F₁ plants.
3. GG-25% Gg-50% Ththe the us, ratio s 1: 2 in F₂ progeny.

Question 2. While playing near a sugarcane field, Mohan noticed that the players were almost similar to one another. At the same time, he noticed the mango trees in the next plot of land which are not similar to one another. Mohan’s brother told Mohan that sugarcane reproduces asexually, hence there is little variation, Mango reproduces sexually, hence there is a larger variation.

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1. Why can sugarcane not reproduce sexually?
2. Can mango reproduce asexually?
3. If a person wants to have a flower garden, what type of plants should he grow?

Answer:

1. Because they do to bear flowers.
2. Yes, by grafting and layering.
3. Since the flower garden will be ornamental the person should plant saplings which are obtained from the same parent asexually. This will give a uniform look to his garden.

Question 3. How do Mendel’s experiments show that the:

1. Traits may be dominant or recessive.
2. Traits are inherited independently?

Answer:

1. When Mendel cross-pollinated pure tall pea plants with pure dwarf pea plants, only tall plants were obtained in the F₁ generation. On self-pollinating the F₁ progeny, both tall and dwarf plants appeared in the F₂ generation in the ratio of 3: 1. Appearance of tall character in both the F₁ and F₂ progenies shows that it is a dominant character. The absence of a dwarf character in the F₁ generation and its reappearance in F₂ shows that dwarfness is the recessive character.
2. When Mendel conducted a dihybrid cross having two sets of characters, he obtained only one set of parental characters in the F₁ generation whereas in the F₂ generation, he obtained both sets of parental characters, now recombined in the ratio of 9:3:3:1.

The appearance of new recombinants in the F₂ generation along with parental type shows that traits are inherited independently.

Question 4.

1. By carrying out experiments with two different traits in pea plants, what did Mendelndal conclude regarding inheritance?
2. Given below is the experiment carried outMendelndal to the udy inheritance of two traits, height and shape of seeds in plantslant. Write appropriate traits in the boxes marked a, b, c, d and

Answer:

1. Mendel concluded after carrying out experiments with two different traits in pea plants that traits are independently inherited, i.e., the inheritance of a pair of factors is independent of the other pair of factors.
2. 1. Dwarf, Round
   2. Tr, Tr (Tall, Wrinkled)
   3. tR, tR (Dwarf, Round)
   4. F₁ generation: TrtR (All tall and round seeds)
   5. [F₂ generation: Tall and Round (TTRR), Tall and Wrinkled (Tr Tr), Dwarf and Round (tt RR), Dwarf and Wrinkled (tt rr)]

Question 5. What are fossils? How are they formed? Describe in brief two methods of determining the age of fossils. State any one role of fossils in the study of the process of evolution.
Answer:

Fossils are preserved remains or impressions of pre-historic organisms in the different strata of the earth’s crust.

Or

Fossils are dead remains of animals and plants from the rom remote past.

Fossils are formed when dead organisms are not completely decomposed. The organisms may get trapped in the resins of the tree, lava of volcanoes or hot mud which, when hardened, retains the animals’ parts thus forming fossils. Two methods of determining the age of fossils are as follows:

1. Relative method- By estimating the age of the layer of earth’s crust where the fossil is found. Fossils near the surface are recent and those in the deeper layers are more The radiocarbon dating method detects the ratios of different isotopes of carbon in the fossils.

Fossils help in determining the connecting links between various groups and their origin from their primitive ones, e.g., Archaeopteryx.

Question 6. Give differences between:

1. Heredity and variations.
2. Dominant and recessive traits.
3. Natural and artificial selection.

Answer:

1. Heredity: It is the transmission of characters from parents to the next generation.
   1. Variations: The changes that occur in the DNA of an organism because of mutations, or by chance.
2. Dominant: The trait which expresses itself even in the presence of contrast. It appears in all the progenies in the F₁ generation.
   1. Recessive: The trait which can express itself only in condition. It does not appear in the F₁ generation.
3. Natural Selection: It is the gradual natural process by which any biological traits become either more or less common in a population, for example maple, a beetlesetle eaten up by a crow, leading to an increase in the population of grbeetlesetle.
   1. Artificial Selection: It is the artificial mechanism of selecting the breeds having desirable characteristics to bring about major changes in plants and animaFor example, different vegetables are generated from wild varieties of cabbage.

Question 7.

1. Why do we say that homozygous plants produce pure progeny?
2. Define heterozygous.
3. Explain how the process of speciation takes place.

Answer:

1. Because of the presence of the same set of genes.
2. Having different pairs of genes.
3. 1. Natural selection.
   2. Geographical isolation, Reproductive isolation.
   3. Genetic drift.
   4. Accumulated variaticausesing changes in the DNA of germ cells to an extent, such as a change in the number of chromosomes. Due to this, the germ cells of the two groups cannot be there. This results in the emergence of a new species.

Question 8.

1. What is geographical isolation?
2. Illustrate ate formation of a species with the help of an example where individuals are very different from each other and one capable of reproduction among themselves.

Answer:

1. Geographical isolation is the isolation of the population by physical barriers such as stretches of water or mountain ranges.
2. There is a population of red beetles living in a mountain area covered with green bushes. Various sub-populations in the large population exist in the neighbourhood. Individuals of a sub-population reproduce sexually among themselves and numerous variations accumulate in these sub-populations of red beetles.

There may be some reproduction among these sub-populations. If a beetle from one sub-population strays on another’s area and some individuals from one sub-population may be carried by predators to the areaanotherther sub-population, then random reproduction takes place. It may leadthe the to migration of genes from one sub-populationanotherther.

If the sub-populations are isolated due to the presenceriversiver between them:

1. Variation will accumulate in isolasub-populationstiThroughoutdgenerationstion, the sub-populations would get very different from each other due to the processes of genetic drift and natural selection and they will not be able to reproduce themselves.

Question 9. Work out which trait would be considered dominant and which one recessive in the given figure

Answer:

1. In a cross between coloured flowered and white flowered plants ts, the F1 generation has all coloured flowered plants. So, the coloured flowered trait is dominant the ver white flowered trait did not express in the F, generation but appears in the F2 generation. So, itaa the recessive trait.

Question 10. Name any five vegetables generated from a common ancestor through artificial selection rather than natural selection. , Also mention the features for which each vegetable is selected.
Answer:

Some of the vegetables generated from a common ancestor, wild cabbage, through artificial selection rather than natural selection, are:

• Cabbies’ age selected fa rom short distance between leaves.
• Broccwas oli selected from arrested flower development and thick stem. Cauliflowers were selected for sterile flowers forming a large flower.
• Kohlrwas abi was selected for a swollen edible stem.
• Kwas ale selected for large leaves.

Question 11. A tall pea plant bearing violet flowers is crossed with a short pea plant bearing white flowers. Work out the F₁ and F₂ generations. Give F₂ ratio.
Answer:

Question 12. Given below is the experiment carried out by Mendel to study the inheritance of two traits in grapes pea:

1. What does A, B, C, D, E, F and G represent in these boxes?
2. State the objective for which Mendel performed this experiment.

Answer:

1. A = gamete of round green (RY) plant

B = gamete of wrinkled (ry)

C = F₁ generational-roundound yellow)

D= 9, E = 3, F = 3, G = 1

2. To show the independent inheritance of traits or to prove the ove law of independent assortment.

Question 13. Does geographical isolation of individuals of a species lead to the formation of a new species? Provide a suitable explanation.
Answer:

Yes, geographical isolation gradually leads to genetic drift. This may impose limitations on the sexual reproduction of the separated population. Slowly the separated individuals will reproduce among themselves and generate new variations.

Continuous accumulation of those variations through a few generations may ultimately lead to the formation of a new species.

Question 14. Bacteria have a simpler body plan when compared with human beings. Does it mean that human beings are more evolved than bacteria? Provide a suitable explanation.
Answer:

This is a debatable issue. the  If appearance of complexity is concurrent with evolution, then human beings are certainly more evolved than bacteria. But if we take the totality of life characteristics into account, then it is hard to label eitorganismisms as evolved.

Question 15. All the human races like Africans, Asians, Europeans, Americans and others might have evolved from a common ancestor. Provide a piece of evidence in support of this view.
Answer:

• All humans are a single species irrespective of their race. All of them have a common body plan, structure physiology and metabolism etc. The earliest member of the species, Homo sapiens, can be traced there.
• All the above evidence could lead the the to result that Africans, Asians, Europeans, Americans and others might have evolved from a common ancestor.

Question 16. Differentiate between inherited and acquired characters. Give one example for each type.
Answer:

• Characters that are passed on from parents to offspring are inherited characters g., the colour of s and the ds, colour of eyes.
• Characters appearing in an individual’s lifetime but which cannot be transmitted to the next generation are acquired characters e.g., obese body, loss of a finger in an accident.

Question 17. Give reasons why acquired characters are not inherited.
Answer:

Acquired characters do not produce changes in the DNA of germ cells, so they cannot be inherited. Only those characters which have a gene for them can be inherited.

Question 18. Evolution has exhibited a greater stability of molecular structure when compared with morphological structures. Comment on the statement and justify your opinion.
Answer:

We see immense diversity in size, form, structure and morphological features in the living world. But at the molecular level, these diverse types of organisms exhibit unbelievable similarity. For instance, basic biomolecules like DNA, RNA, carbohydrates, proteins, etc., exhibit remarkable similarity in all organisms.

Question 19. In the following crosses write the characteristics of the progeny

Answer:

1. Round, yellow
2. Round, yellow Round, green Wrinkled, green Wrinkled, yellow
3. Wrinkled, green
4. Round, yellow

Question 20. In question 9, what are the combinations of characters in the F₁ progeny? What are their ratios?
Answer:

1. Round Yellow – 9
2. Wrinkled yellow – 3
3. Round Green – 3
4. Wrinkled green – 1 9:3:3:1

Question 21. How is the study of fossils considered significant?
Answer:

The fossil study is considered significant because a broad historical sequence of biological evolution can be built The phylogeny of man, horse and elephant has been worked out.

1. Habits and behaviour of extinct species can be inferred.
2. Reliable information on ancient environments and climate can be obtained.
3. Fossils provide direct evidence of past life.
4. The provides convincing proof of organic evolution.

Question 22. Suggest with reason, which of the following are homologous and which are analogous organs

1. Scalesfishshes and Shell of mollusc
2. The trunk of an elephant and the hand of a Chimpanzee
3. The wing of a bird and the wing of a bat
4. The nails of a human being and the claw of a cat
5. Ginger and sweet potato.

Answer:

1. Fish Scales and Mollshellshell are analogous structures because both are protected but differ in origin trunkrunk of the elephant the and hand of a Chimpanzee are analogous structures because both are prehensile in functioning but differ in origin (The elephant trunk is an extension of the proboscis) and the structure winging of a bat and wing of a bird are analogous structures, both are similar in functioning but differ in origin nails of hubeingseing and claw of cat are homologous structures because these are similar in origin a differ in functioning.
2. Ginger and Sweet potato are structures although these are storage structures. Because ginger is a stem modification while sweet potato is a root modification.

Magnetic Effects Of Electric Current Long Answer Questions Answer The Following Questions

Question 1. Explain with the help of the ring system of wiring in domestic wiring
Answer: The ring system is as shown in the figure below:

It consists of a ring-circuit. Wires starting from the main fuse box run around all the main rooms ofthe house and then come back to the fuse box again. The fuse box contains a fuse of about 30 A.

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A separate connection is taken from the live wire ofthe ring for each appliance. The terminal of the appliance is connected to the live wire through a separate fuse and a switch. If the fuse of one appliance burns, it does not affect the other appliance. For each appliance, the wires used for connection should be of proper current carrying capacity.

Question 2. The figure shows a closed coil connected to a galvanometer G. The galvanometer shows a deflection to the right when the N-pole of the bar magnet is brought closer to the coil. Why does the deflection occur in the galvanometer?

1. State the observation when
2. The coil is moved away from the N-pole.
3. Both the coil and magnet are moved to the right with the same speed

Answer: As the magnet is moved closer to the coil, the flux linked with the coil increases. This sets up an induced current in the coil as shown by deflection in the galvanometer.

The direction of induced current in the soil AB is reversed and the galvanometer shows a deflection to the left.

When both the magnet and the coil are moved towards the right with the same speed, the flux linked with the coil does not change. No induced current is set up. Hence no deflection is shown by the galvanometer.

Question 3. A coil made of insulated copper wire is connected to a galvanometer.

What will happen to the deflection ofthe galvanometer if the coil is moved towards a stationary bar magnet and then moved away from it? Give a reason for your answer and name the phenomenon involved.

Answer: When the coil is moved towards the bar magnet, the galvanometer shows deflection in one direction.

Reason: When the coil is moved towards the stationary bar magnet, the magnetic flux linked with it increases and a current is induced in it, as is shown by deflection in the galvanometer.

When the coil is moved away from the coil, the galvanometer shows deflection in
opposite direction.

Reason: When the coil is moved away from the magnet, the magnetic flux linked with it decreases and a current is induced in the coil in the opposite direction, as shown by deflection in the galvanometer in the opposite direction. This phenomenon is called electromagnetic induction.

Question 4. Draw the magnetic field lines of the field produced by a current-carrying circular loop. Explain with reason whether the field will be stronger at a point at the center loop or near the circumference of the loop.
Answer: Magnetic field due to a current through a circular loop-. The given figure shows the magnetic field lines of a circular wire carrying a current. The lines of force near the wire are almost concentric circles. As we move toward the center of the loop, the concentric circles become larger and larger.

Near the center of the loop, the arcs ofthese big circles appear as parallel straight lines. Thus the magnetic field is almost uniform at N the centre of the loop. By applying the right-hand rule, we can see that the magnetic field lines due to all sections of the wire are in the same direction within the loop. That is why the field is stronger at the center or near the circumference of the loop.

Question 5. Name two electrical appliances of daily use in which an electric motor is used.

Name and state the principle on which an electric motor works.

Answer: Electric motor is commonly used in fans, washing machines, mixers, etc. An electric motor works on Fleming’s left-hand rule.

Fleming’s left-hand rule: When we stretch our thumb, forefinger, and middle finger so that they are mutually perpendicular to one another, the forefinger points in the direction of the magnetic field, and the middle finger points in the direction of the current; the thumb gives the direction of the force acting on the conductor.

Question 6. What is an electromagnet? What decides its polarity’? How does it differ from a permanent magnet? List the three factors and explain how the strength ofan electromagnet depends on these.
Answer: When a soft iron is placed inside a solenoid and current is passed through it, then the soft iron gets magnetized. The magnet so formed is called an electromagnet. Its polarity is decided by the direction of current flowing through the solenoid.

1. Permanent magnets have a constant magnetic field around them whereas the magnetic field of the electromagnet is temporary.
2. The strength of an electromagnet depends on:
3. The number of turns in the solenoid.
4. Strength of current flowing through the solenoid.
5. Position of the soft iron core within the solenoid.

Question 7. 1 Draw a magnetic field, lines of a bar magnet. “Two magnetic field lines never intersect each other”. Why? An electric oven of 1.5 kW is operated in a domestic circuit (220 V) that has a current rating of 5 A. What result do you expect in this case? Explain.

Answer: Magnetic field lines around a bar magnet.

If two magnetic field lines intersect at a point, then at the point of intersection, there must be two directions ofthe same field, which is not possible.

Here, P = 1.5 kW = 1500 W.

Current \(I=\frac{P}{V}=\frac{1500}{220}=7 \mathrm{~A}\)

1. Thus, the current flowing through the circuit when the oven is ON is nearly 7 A which is higher than the current rating (5 A) of the circuit.
2. The wiring ofthe circuit may burn, fuse wire will also blow off breaking the circuit and stopping the current supply.
3. Explain any three properties of magnetic field lines.
4. Give two uses of the magnetic compass.

Answer: Field lines emerge from the north pole and merge at the south pole outside the magnet.

1. They are closed curves.
2. Magnetic force is greater where the field lines are crowded.
3. No two field lines are found to cross each other.

Uses of magnetic compass:

1. A magnetic compass can be used to find directions.
2. It can be used to test if a substance has magnetic properties.

Question 9. Write the values ofthe following physical quantities in connection with the domestic power supply in our country:

1. The potential difference between a live wire and a neutral wire is the frequency.
2.  Explain the role of the following as safety measures in domestic electric appliances! circuits
   1. Earth Wire
   2. Fuse
   3. 220v
   4. 50Hz

Answer: 3. 220 V

2. (1) Earth wire: The earth wire is a thick metal wire connected to a metal plate dug deep into the earth and is used as a safety measure for an appliance with metallic bodies, for example, toasters, etc. The metallic body is connected to the earth wire which provides a low resistance conducting path for the current.

It also ensures that any leakage of current in the metallic body keeps its potential to that of the earth and the user does not get a severe electric shock if touched.

(2) Fuse: It is a piece of wire made of an alloy with a low melting point. If a current larger than the specified value flows through the circuit, the temperature of the fuse wire increases and it melts. This breaks the circuit and thus prevents the flow of undue high electric current in the device. In this way, a fuse of proper rating protects the appliance and the circuit from damage.

Question 10.

1. The given figure shows a domestic electric circuit. Study this circuit carefully. List any two errors in the circuit and justify your answer.
2. Give one difference between the wires used in the element ofan electric heater and a fuse.
3. List two advantages of parallel connection over series connection.

Two errors are:

1. The fuse is incorrectly connected to the neutral wire (N), it must be connected to the live wire (L).
2. Bulb B2 is not connected to the neutral wire.
3. Element of an electric heater – high melting point. Element of a fuse wire – low melting point.
4. Each appliance has an equal potential difference.
5. Each appliance has a separate switch to ON/OFF the flow of current through it.

Question 11. What is electromagnetic induction?

1. Explain the various methods of producing induced current.
2. State the rule which gives the direction of induced current.
3. Name two devices that work on the principle of electromagnetic induction.

Answer: The process by which a changing magnetic field in a conductor induces a current in another conductor is called electromagnetic induction.

1. By moving a magnet towards or away from a coil.
2. By varying, the current in one coil, induced emf is produced in the coil.

Fleming’s right-hand rule:

• AC and DC electric generator.

Question 12. What is the direction of magnetic field lines outside a bar magnet?

1. Why two magnetic field lines cannot intersect each other?
2. What is indicated by crowding of magnetic field lines in a given region?
3. What is the frequency of AC in India?
4. State one advantage of AC over DC.

Answer: North pole to South pole.

1. Because it would mean that at the point of intersection, the compass needle would point in two directions which is not possible.
2. The strength of the magnetic field is higher in that region.
3. 50 Hz
4. AC can be transmitted over long distances without much loss of energy.

Question 13. Draw a labeled diagram ofan electric motor. Explain its principle and working. What is the function of a split ring in an electric motor?
Answer: An electric motor is a rotating device that converts electrical energy into mechanical energy.

Principle: An electric motor works on the principle that a current-carrying conductor placed in a magnetic field experiences a force, the direction of force is given by Fleming’s left-hand rule.

Construction: As shown in the given figure, an electric motor consists of the following main parts:

Field magnet: It is a strong horse-shoe type magnet with concave poles.

Armature: 2 is n rectangular coil ADCD having n large number of turns of thin insulated copper wire wound over a soil iron core.

Split ring commutator: It consists of a cylindrical metal ring split into two halves S1 and S2. The two ends A and D ofthe armature coil are connected to the split rings S( and S., respectively.

Brushes: Two graphite or flexible metal rods maintain a sliding contact with split rings S, and S2, alternately.

Battery: A battery of a few cells is connected to the brushes. The current from the battery flows to the armature coil through the brushes and the split rings.

Working: Initially, suppose the plane ofthe coil is horizontal. The split ring SL touches the brush Bx and split ring S2 touches the brush B2. The current in the coil flows in the direction ABCD, as shown in the figure.

The currents in arms AB and CD are in opposite directions. The magnetic force acting on arm AB pushes it downwards while the force acting on arm CD pushes it upwards. Thus, the armature coil along with the axle rotates anticlockwise.

After half a rotation, the split ring Sx comes in contact with brush B9 and S2 in contact with brush Br Therefore, the current flows along the path DCBA. Thus, the arm AB is now pushed up and the arm CD is pushed down.

Therefore, the coil and the axle rotate half a turn more in the same direction. The reversing ofthe current is repeated at each half-rotation, giving rise to a continuous rotation of the coil and the axle.

The function of the split ring commutator is to reverse the direction of current in the armature coil after every half rotation.

Question 14. Explain the underlying principle and working of an electric generator by drawing a labeled diagram. What is the function of brushes?
Answer: AC Generator: It is a device that converts mechanical energy into alternating forms of electrical energy.

Principle: It works on the principle of electromagnetic induction. When a closed coil is rotated in a uniform magnetic field with its axis perpendicular to the magnetic field, the magnetic field lines passing through the coil change, and an em is induced and hence a current is set up in it.

Construction: It consists of the following main parts:

Field magnet: It is a strong horseshoe-type permanent magnet with concave poles.

Armature: ABCD is a rectangular armature coil. It consists of a large number of turns of insulated copper wire wound on a soft iron cylindrical core.

Slip rings: These are two brass rings S1 and S2 rigidly connected to the two ends of the armature coil.

Brushes: These are two graphite rods B1 and B2 which are kept pressed against the slip rings S and S2.

Working: Suppose the armature coil ABCD is in the horizontal position. Now the coil is rotated clockwise. The coil cuts the magnetic lines of force. The arm AB moves upwards while the arm CD moves downwards.

According to Fleming’s right-hand rule, the induced current flows from A to B in arm AB and C to D in arm CD i.e., the induced current flows along ABCD. The induced current flows in the circuit through brush B2 to Br After half the rotation of the armature, the arm CD moves upwards and AB moves downwards.

The induced current now flows in the reverse direction i.e., along DCBA. The current flows from B1 to B2.

Thus the direction of current in the external circuit changes after every half rotation. Such a current that changes its direction after equal intervals of time is called alternating current. This device is called an AC generator.

Question 15. The diagram below shows two ways of connecting three bulbs A, B, and. C to 220 Vmains in a room. Name the two arrangements. Which of them would you prefer for household electricity? Give two reasons.

Answer: The arrangement shown in the figure is a series arrangement. The arrangement in the figure is parallel.

We would prefer the parallel arrangement. The reasons are:

1. In a series arrangement, if one of the bulbs is fused, the other bulbs also fail to glow. But in a parallel arrangement, if one bulb fuses, the other bulbs continue to glow.
2. In a series arrangement, while one bulb glows if the other bulb is switched on, the resistance ofthe circuit increases, and hence the bulbs glow less brightly. But in a parallel arrangement, each bulb glows at the same voltage, therefore, the glow of a bulb is unaffected if another bulb is switched on.

Question 16. Have you just paid the electricity bill for your house? If yes, What was it that your family consumed for which you had to pay? In what unit was it measured?
Answer: Yes;

1. The family consumed electrical energy.
2. Kilowatt-hour (kWh)

The figure shows a long solenoid, a cylindrical coil of several turns of insulated copper wire, connected to a battery through an ammeter A and a rheostat Rh.

Which end of the solenoid is an N-pole and which end is an S-pole?

Draw the magnetic field lines inside the solenoid and indicate their directions. Are magnetic field lines closed?

How can you increase the strength ofthe magnetic field inside the solenoid? Give two methods.

Answer: P is the south pole and Q is the north pole.

1. Yes, the magnetic field lines are closed.
2. By increasing the current flow.
3. By increasing the number of turns ofthe solenoid.

The substances that have the property of attracting small pieces of iron, nickel, cobalt, etc. are called magnets. Pieces of iron and other magnetic materials can be made to acquire the properties of natural magnets.

1. What is the origin of the word magnetism?
2. Give two properties of magnets.
3. Agnesia Where The Natural Magnets Were First Found.
4. Magnets have both attractive and directive properties.

Question 17. A magnet produces a magnetic field in the space around it, which exerts a force on any other magnet placed in it. Field lines are used to represent a magnetic field. A field line is the path along which a hypothetical free north pole would tend to move. The direction ofthe magnetic field at a point is given by the direction that a north pole placed at that point would take. Field lines are shown closer where the magnetic field is greater.

1. What is a magnetic field line?
2. Can two magnetic field lines intersect? Justify.
3. Give two properties of magnetic field lines.

Answer: A magnetic field line may be defined as the curve the tangent to which at any point, gives the direction of the magnetic field of that point.

1. Number If two magnetic field lines intersect, then there will be two tangents and hence two directions of magnetic field at the point ofintersection which is not possible.
2. The magnetic field lines are closed curves that start in air from the N-pole end at the S-pole and then return to the N-pole through the interior of the magnet.
3. Field lines are closer together in the regions of strong fields and farther apart in the regions of weak fields.

Question 18. When a wire carries more current than it can carry without overheating, it is said to be overloaded. An event in which a large current passes through the wires when the neutral wires touch accidentally is called a short circuit. An overload or a short circuit causes.

1. Excess heating ofthe wires, which may even cause a fire. To prevent this, fuses or circuit breakers are used. To prevent electric shocks in the event of the live wire touching the metallic body ofan appliance, the body is connected to the earth wire.
2. What is meant by overloading ofan electric circuit?
3. What is short-circuiting?
4. What precautions should be taken to avoid overloading of domestic electric circuits?

Answer: If the current drawn from the mains exceeds the safety limit, then this is known as overloading of the circuit.

When the live wire comes into contact with the neutral wire, the resistance becomes almost zero, and a very large current flows through the circuit. This is called short-circuiting.

The circuit must be divided into different sections and a safety fuse must be used in each section. High-power appliances like air-conditioners, refrigerators, water heaters, etc. should not be used simultaneously.

Question 19. Student experiments to study the magnetic effects of current around a current-carrying conductor. He reports that the direction of the north pole of a compass needle kept at a given point near the conductor gets reversed when the terminals ofthe battery are interchanged.

1. What is the nature of the magnetic field of, a straight current-carrying conductor?
2. Name and state a rule for finding the direction ofthis field.
3. Give two factors on which the magnitude of the field depends.

Answer: Magnetic fields are concentric circles with their centers of wire.

1. Right-hand thumb rule.
2. Current through conductor
3. Distance from the conductor

Question 20. Draw a labeled circuit diagram of a simple electric motor and explain its working. In what way these simple electric motors are different from commercial motors’?
Answer: The circuit diagram of a simple electric motor is shown below.

Working:

Let coil ABCD be in a horizontal position. When the key is switched on, the current flows in the direction of DCBA and then leaves through the brushes B2 via ring R2.

Applying Fleming’s left-hand rule, no force acts on arms BC and AD as they are parallel to a magnetic field, arm AB experiences a force in a downward direction and arm CD experiences an equal force in an upward direction. A torque acts on the coil and it rotates in the anti-clockwise direction.

While rotating, the coil reaches the vertical position, brushes loose contact with the rings and the current stops flowing. However, the coil does not stop due to the inertia of motion.

When the coil passes the vertical position, the rings automatically change their positions and come in contact with opposite brushes.

This reverses the direction of current through the coil but the direction of current on the right-hand side remains the same.

So, the force on the right-hand side is always upward and the force on the left-hand side is always in a downward direction. Thus, the coil continues in to anti-clockwise direction.

A commercial electric motor uses the following:

1. An electromagnet in place of a permanent magnet.
2. A large number of turns of conducting wire in the current carrying coil.
3. A soft iron core on which the coil is wound. The combination of soft iron core and coil is an armature. It enhances the power of motors.
4. Thus, commercial electric motors do not use permanent magnets to rotate the armature because permanent magnets are weak and do not produce a strong magnetic field in the region.

Question 21. Explain the phenomenon of electromagnetic induction. Describe an experiment to show that a current is set up in a closed loop when an external magnetic field passing through the loop increases or decreases.
Answer: This phenomenon was discovered by Michael Faraday and Joseph Henry in 1831. The phenomenon of generation of electric current in a closed circuit from magnetic effects i.e., by changing the magnetic field is called electromagnetic induction. The electric current produced due to this phenomenon is called induced current.

The potential difference set in the circuit due to induced current is called induced EMF.

Experiment: Let two different coils of copper wire, namely coil 1 and coil 2, having a large number of turns be arranged as per the circuit diagram as shown in the figure.

Coil 1, having a larger number of turns, is connected in series with a battery and a plug key whereas the other coil 2 is connected with a galvanometer as shown in the circuit diagram.

When key K is closed, the galvanometer shows a deflection in its needle that instantly jumps to one side, and just as quickly returns to zero, indicating a momentary current in coil 2.

This happens due to an external magnetic field passing through the loop increases. When the key is open, coil 1 is disconnected from the battery. The needle momentarily moves but to the opposite side.

It means that now the current flows in the opposite direction in coil 2. This happens due to an external magnetic field passing through the loop decreases.

Question 22. Describe the working of an AC generator with the help of a labeled circuit diagram. What changes must be made in the arrangement to convert it to a DC generator?
Answer: Principle: The electrical generator works on the principle that when a straight conductor is moved in a magnetic field, then current is induced in the conductor. The direction of this induced current is given by Fleming’s right-hand rule.

Construction of AC generator: It consists of a rectangular coil ABCD which can be rotated rapidly between N and S poles of a strong horse-shoe-shaped magnet having radial ends. The coil is made of a large number of turns of insulated copper wire. The ends A and D of the coil are connected to slip rings R1 and R2.

As the slip rings R1 and R2 rotate with the coil, the two carbon brushes B1 and B2 keep contact with them. Outer ends of the two brushes B1 and 132 are connected to the galvanometer to show the flow of the current in the given external circuit.

Working: When the coil starts rotating with the arm AB moving up and the arm CD moving down, cutting the magnetic lines of force, then according to Fleming’s right-hand rule an induced current is set up in these arms along the direction ofAB and CD.

So an effective induced current flowing in the direction of ABCD is obtained. If there are a large number of turns in the coil, the current generated in each turn adds up to give a large quantity of current through the coil.

After half rotation of the coil, its arm CD starts moving up and AB moving down. As a result, the direction of the induced current gets reversed in the coil in the direction of DCBA. Thus, after every half rotation the polarity ofthe current in the respective arm changes.

To convert an AC generator into a DC generator, a split ring commutator is used. This helps in producing direct current.

Question 23. Draw an appropriate schematic diagram showing common domestic circuits and discuss the importance of use. Why is it that a burnt-out fuse should be replaced by another fuse of identical rating?
Answer: A fuse in a circuit prevents damage to the appliances and the circuit due to overloading. Otherwise, the appliances or the circuit may get damaged. It stops the flow of unduly high electric current. The fuse is placed in series with the device.

A fuse wire works because of its lower melting point which is possible. If a fuse with a larger rating is used with an appliance, the fuse wire shall not melt and hence would fail to serve the required purpose. Due to this a fuse with a defined rating should not be replaced by one with a larger rating.

Question 25. Describe the activity that shows that a current-carrying conductor experiences a force perpendicular to its length and the external magnetic field. How does Fleming’s left-hand rule help us to find the direction ofthe force acting on the current-carrying conductor?
Answer: Aim: To show that force is exerted on a current-carrying conductor placed in a strong magnetic field.

Materials required:

A conducting rod (AB), connecting wires, horse-shoe magnet, battery switch, and clamp stand.

Procedure:

1. Connect the conducting rod (AB) to the battery and key
2. Place a strong horse-shoe magnet in such a way that the rod AB lines between the poles with a magnetic field directed upwards i.e. N. Pole is vertically above the rod.
3. Plug the key.

Observation: A current-carrying rod AB experiences a force perpendicular to its length and the magnetic field.

According to Fleming’s left-hand rule, stretch the thumb, the forefinger, and the middle finger of your left hand such that they are mutually perpendicular. If the forefinger points in the direction of the magnetic field and the middle is the direction of current, then the thumb will point in the direction of motion or force acting on the conductor.

NCERT Solutions For Class 10 Science Chapter 14 Sources Of Energy Long Question And Answer

Question 1. What is a good source of energy?
Answer: A good source of energy would depend on the requirement for which energy is needed.

For example, we use one source say gas for cooking food and another source say electricity for heating a room. In general, a good source of energy would be one

1. Which would do a large amount of work per unit mass/volume.
2. Which would be easily accessible.
3. Which can be easily stored and transported.
4. Which is also reasonably economical
5. It could cause the least environmental damage.

Question 2. What is a good fuel?
Answer: The following should be the characteristics of a good fuel:

Read and Learn More Class 10 Science Solutions

1. It should be fairly cheap.
2. It should be easily available.
3. Its ignition temperature should be well above normal temperature.
4. It should be conveniently handled and transported.
5. It should not produce, during burning, any poisonous materials or irritating fumes etc.
6. Its combustion rate should be steady and controllable.
7. It should not leave any residue or ash after burning.
8. It should bum in a way that can be controlled.
9. It should produce a large amount of heat per unit vol. or mass.

Question 3. What is nuclear energy? What is nuclear fission? How is nuclear energy used for peaceful purposes?
Answer: When the nucleus of an unstable atom breaks up or a radioactive substance emits radiations (a, p, yrays), the energy so released together with radiations is called nuclear energy.

This process is called nuclear fission. This nuclear energy when used in a controlled manner finds use in the following fields:

1. In curing diseases, for example, tumours and cancer.
2. Radio isotopes are nowadays used in research in various fields like industry, agriculture, science etc.
3. Preservation of food, e.g., potatoes can be preserved for long periods if irradiated with y-rays.
4. In determining the age of archaeological remains of wood by a process known as
   carbon dating.
5. As a fuel—a small amount of fuel produces a large amount of energy.

Question 4. Name the three forms in which energy from oceans is made available for use. What are OTEC power plants? How do they operate?
Answer: The three forms of energy from the oceans are:

1. Tidal energy
2. Ocean wave energy and
3. Ocean thermal energy.
4. The devices used to harness ocean thermal energy are called Ocean Thermal Energy
   Conversion (OTEC) power plants.

In one of the OTEC power plants, the warm surface water is used to boil ammonia. The vapours of this liquid are then used to drive turbines and hence generators. The cold seawater is pumped up again to convert ammonia into vapour. This system can be operated 24 hours a day.

Question 5. What is geothermal energy? How can it be utilized?
Answer: Due to high temperatures in the interior of the earth the rocks present there melt which is known as magma. Due to some geological changes inside the earth, this magma is pushed upward and is trapped at some depth below the surface of the earth.

These are called hot spots and serve as the source of geothermal energy. Water is trapped in the earth at several places.

At places where trapped water comes in contact with hot spots, it gets converted into steam. Since this steam remains trapped between rocks, it gets compressed to a very high pressure.

On drilling and introducing pipes upto the compressed steam, the trapped steam can be driven out at high speed. This can be utilized to turn the turbines and generate electricity.

In some places, steam and hot water find their way through large cracks between rocks and serve as natural geysers.

Question 6. What are semiconductors? Explain the principle of working of solar cells made of semiconductors. Why are solar panel cells used in artificial satellites?
Answer: Semiconductors are certain types of metals which allow only partial current to pass through them in one direction only. The conductivity of semiconductors increases when light falls on them. Their conductivity also increases if certain impurities are added to them. Materials like silicon, selenium, cadmium sulphide or copper sulphide act as semiconductors.

In a solar cell, the pieces (waters) of semiconducting materials containing impurities are so arranged that a potential difference develops between two regions of the semiconductors when light falls on them.

Thus, when solar radiations fall in solar cell, it converts solar energy into electrical energy. A lead storage battery is connected to the circuit which gets charged and can be used as and when desired. The power generated by a single solar cell is very low.

A single solar cell with an area of 4 cm2 has an output voltage of about 0.4-0.5 volts at 60 milliamperes of current. Therefore, a large number of solar cells are mounted together to generate appreciable electrical power.

The solar cells are arranged in series to form solar panels. Solar panel cells are mostly used in space satellites which remain in outer space for many years.

The space satellite contains solar panels which convert sunlight energy into electrical energy and thus electrical energy is used by the satellite to operate various functions.

Question 7. What is hydroelectricity? Explain the basic principle involved in the generation ofthis energy.
Answer: The electricity generated by using the energy of flowing water is called hydroelectricity. The basic principle of the generation of hydroelectricity is as follows:

The water flowing in a river is collected by constructing a high-rise dam D. This water, which has been stored at a high altitude, has a lot of potential energy in it.

The water stored in a high-rise dam is allowed to fall on a water-turbine G located near the base of the dam.

When the fast-moving water falls on the blades of a turbine, then the kinetic energy of fast-moving water rotates the turbine rapidly.

The shaft of the turbine is connected to the coil of an electricity generator or dynamo. So, when the water turbine rotates rapidly, the generator coil fixed on its shaft also rotates rapidly and produces electricity.

Question 8. With the help of a labelled diagram, explain the construction and working of a solar water heater.
Answer: The solar water heater consists of an insulated metallic box which is painted black from inside and outside.

In this box, copper tubes painted black from the outside, are fitted in a zigzag shape. The box and copper tubes are painted black so that they may absorb the maximum radiant heat energy of the sun efficiently.

The box is covered with a glass sheet lid to trap sun rays by producing a greenhouse effect.

The two ends of copper tubes are joined to a water storage tank as shown in the figure. The solar water heater and its water storage tank are fitted on the roof of a building, so that they may absorb the maximum radiant heat energy of the sun.

Working of Solar Water Heater: When the sun shines the radiant heat energy enters the metal box through a glass sheetlid and is absorbed by water present in copper tubes.

This water gets heated and it comes out through the other end of copper tube A and goes into the storage tank.

As long as the sunshine is there, the water keeps circulating between the solar heater box and the insulated storage tank. The water keeps on circulating on its own because water on getting hot expands and pushes itself into the copper tube

Now to replace this hot water, fresh cold water moves into the copper tubes. In this way, all the water in the storage tank gets heated which can be taken out for use from the tap attached to the pipe.

Question 9. Draw a schematic labelled diagram of the type of solar cooker. Name two components of the solar cooker which are responsible for increasing the temperature inside the solar cooker. Explain their function.
Answer: A schematic diagram is as shown:

Two components of the solar cooker are a plane mirror and a Glass sheet.

Functions: The plane mirror maximizes the amount of light/heat entering the solar cooker. The glass sheet traps the infrared radiation or produces a greenhouse effect.

Question 10. Name the major fuel component of biogas. What are its other combustible components? Draw a simple labelled diagram of a fixed dome-type biogas plant. What is the use of residual slurry and why?
Answer: The major fuel components of biogas are:

1. Methane, CO2 and traces of other gases.
2. The spent slurry is used as manure as it is rich in nitrates and phosphates.

Question 11. What is a windmill? With the help of a diagram, describe in brief the construction and working of the windmill. Give uses of wind energy.
Answer: A windmill is a machine which works with the energy of blowing wind. It can be used to run water pumps (to draw water from the ground) and also for grinding grains.

It consists of a circular wheel to which blades are attached radially to catch the wind. The centre of this circular wheel is connected to one end of the crank rod. The U-bend of the crank is connected to the pump rod (piston rod).

Working: When the blowing wind strikes across the blades of a windmill, the KE of wind rotates the blades continuously, as a result crank attached to them rotates.

Now, when the crank rotates, its U-bend lifts the pump rod up and down continuously. This pump rod now operates the pump which lifts the underground water.

Uses of wind energy:

1. Wind energy is used to propel sailboats to transport men and materials from one
   place to another.
2. Wind energy is used to run water pumps to draw out underground water.
3. Wind energy is used to run flour mills to grind the grains.
4. Wind energy is used to generate electricity.

Question 12. What is the basic cause for winds to blow? Name a part of India where wind energy is commercially harnessed. Compare wind power and the power of water flow concerning generating mechanical and electrical energies. What is the hindrance to developing them?
Answer: Sun’s energy is one of the main factors responsible for the movement of air/wind in the atmosphere.

Kanyakumari in Tamil Nadu India is the place where wind energy is commercially harnessed. The power of flowing water is more than that of wind and as such flowing water produces more energy than the wind.

1. The source of wind power i.e., Air and the source of flowing water power i.e., water are inexhaustible and reversible sources.
2. Wind power and flowing water do not cause any pollution.
3. The kinetic energy of wind and flowing water gets transformed into electrical energy.
4. Wind and water are available free of cost.

Limitations of wind energy:

1. It is not available all the time and at all the places for doing various types of work.
2. Wind energy farms can be established only in those places where the wind blows for the greater part of the year and there is no place in the world where the wind blows all the time.

Limitations of flowing water energy:

1. The construction of dams on rivers results in a variety of ecological changes in the downstream area of the river.
2. The flowing water is not available in plenty everywhere to turn the water wheels
   and run the machines.

Question 13. Describe the steps involved in obtaining biogas and explain what is meant by anaerobic decomposition.
Answer: A slurry of animal dung, for example, cow dung and water is made in the mixing tank from where it is fed into the digester. The digester is usually a closed underground tank made by laying bricks.

1. In the digester, the action of microorganisms breaks down or decomposes the complex compounds of the biomass in the slurry.
2. Anaerobic microorganisms, in the presence of water, do the degradation of biomass in the digester.
3. Since anaerobic microorganisms do not require oxygen, the digesters are designed like a sealed chamber. This process takes a few days to complete during which gases like methane; carbon dioxide, hydrogen and hydrogen sulphide are produced.
4. Biogas, which is a mixture of these gases, is supplied to consumers through pipes. The fermentation is carried out by anaerobic bacteria in the presence of water but in the absence of oxygen.
5. The anaerobic bacteria decompose the carbon compound present in the animal and plant wastes in the form of carbohydrates, proteins and fats into methane gas. This is called anaerobic decomposition.

Question 14. Why are fossil fuels classified as non-renewable sources of energy? What steps should be taken to conserve these sources?
Answer: The term fossil means the remains of prehistoric plants and animals buried under the earth millions of years ago which may be due to some natural calamity.

1. Fossil fuels are formed from dead plants and animals which got buried deep in the earth and covered with sediments like mud and sand in the absence of oxygen.
2. Chemical reactions, high pressure, heat and the action of anaerobic bacteria converted these fossils into fossil fuels like coal, petroleum and natural gas. This happened throughout millions of years due to certain slow changes under special circumstances.
3. Since these conditions are not prevailing now, therefore, no new fossil fuels are being formed now. Hence, they have been classified as non-renewable sources.

The following steps should be taken to conserve these fuels: Use of alternative forms of energy like solar energy; waste biomass energy; sea wave energy: tidal energy; geothermal energy; wind energy and fusion energy. Understand that “Energy saved is energy produced”. Therefore, try to use energy judiciously. Do not waste energy uselessly.

Put off all the lights and fans in your school, home and other places if they are not being used. Use geysers, electric irons and other energy-consuming appliances carefully.

Do not unnecessarily use motor vehicles unless four to five persons are required to travel to reach a destination. Use public transport instead. Such small steps taken by all of us can save the earth from the energy getting exhausted.

Question 15. What is the process used to harness nuclear energy these days? Explain it briefly.
Answer: Nuclear reactoris the process used to harness nuclear energy these days.

Nuclear fission reaction takes place in the nuclear reactor. The reaction in which a heavy nucleus splits into two or smaller nuclei with the evolution large amount ofenergy when it is bombarded with slow-moving neutrons is called nuclear fission.

The nucleus of a heavy atom (such as uranium, plutonium or thorium), when bombarded with low-energy neutrons, can be split apart into lighter nuclei along with the release of a tremendous amount ofenergy; U-235 nucleus splits up broadly into two groups of nuclei.

1. A heavy group of nuclei, with mass number in the range A = 130 to A = 149.
2. A light group of nuclei, with mass number in the range A = 85 to A = 104.

In the form of a nuclear reaction, we represent the nuclear fission of U-235 as follows:

⇒ \({ }_{92}^{235} \mathrm{U} \xrightarrow[\text { Slow moving }]{\frac{1}{\mathrm{n}}}{ }_{92}^{236} \mathrm{U} \longrightarrow{ }_{56}^{144} \mathrm{Ba}+{ }_{36}^{89} \mathrm{Kr}+3{ }_0^1 \mathrm{n}+\text { Energy (in huge amount) }\)

The major hazards of nuclear power generation are as follows:

1. The improper nuclear waste storage and disposal may result in environmental
   contamination.
2. There is a risk of accidental leakage of nuclear radiation and its leakage causes huge losses to living things.
3. The high cost of installation of nuclear power plants high risk of environmental contamination and limited availability.
4. How can solar energy be harnessed? Mention any two limitations in using solar energy.
5. How are these limitations overcome?
6. Solar energy can be harnessed directly as well as indirectly which is as follows:

Direct utilisation: The direct utilisation of solar energy can be done either by collecting it as heat or by converting it to electricity

Indirect utilisation: It can be done by converting solar energy into chemical energy like biomass of plants etc.

1. The limitations of using solar energy are as follows:
2. Energy reaching the surface is very much diffused, so direct utility is limited.
3. It is not available uniformly all the time and in all the places.

Make a list of conventional and non-conventional sources ofenergy. Give a brief description of harnessing one non-conventional source ofenergy.

Conventional: Fossil fuels, water, wind, biomass etc.

Non-conventional: Nuclear, Solar, Energy from the ocean, Geothermal.

Nuclear energy: Nuclear energy is produced by the release ofheat from unstable elements such as uranium. The energy is harnessed by using the energy to heat water.

Why is there a need for harnessing non-conventional sources ofenergy? How can energy be harnessed from the sea in different ways?

There is a need for harnessing non-conventional sources of energy because of the following reasons:

The energy demand is increasing day by day to meet the basic requirements of our changed lifestyles, growing use of machines and industrialisation to improve our living standards.

Fossil fuels are non-renewable sources of energy and were formed millions of years ago and there are only limited reserves of fossil fuels.

The energy from the sea can be harnessed in different forms which are as follows:

Tidal energy. It is harnessed by constructing a dam across a narrow opening to the sea. A turbine fixed at the opening of the dam converts tidal energy to electricity.

Wave energy. A wide variety of devices have been developed to trap huge waves near the regions for the rotation of turbines and the production of electricity.

Ocean thermal energy: The water at the surface of the sea or ocean is heated by the sun while the water in deeper sections is relatively cold. This temperature difference is exploited to obtain energy in ocean thermal energy conversion plants.

1. These plants can operate if the temperature difference between the surface water and water at depths up to 2 km is 293 K (or 20°C) or more The warm surface water is used to boil a volatile liquid like ammonia. The vapours of the liquid are then used to run the turbine of the generator.
2. The cold water from the depths of the oceans is used to condense vapour again into liquid. The devices used to harness this form of ocean energy are known as Ocean Thermal Energy Conversion [OTEC] power plants.

Question 16. What are the environmental consequences of using fossil fuels? Suggest the steps to minimise the pollution caused by various sources ofenergy including non-conventional sources ofenergy.
Answer: Environmental consequences ofusing fossil fuels: Airpollution, Greenhouse effect, Environment consequences: acid rain, global warming etc.

The following are the steps to minimise the pollution caused by various sources ofenergy including non-conventional sources of energy:

1. The air pollution caused by the burning of coal or petroleum products can be reduced by afforestation.
2. Proper and safe disposal of nuclear wastes.

Question 17. Energy from various sources is considered to have been derived from the sun. Do you agree? Justify your answer.
Answer: Yes, the sun is the ultimate source of energy directly or indirectly, all forms of energy are derived from solar energy for ofthe following reasons:

Non-renewable sources of energy: Fossil fuels like coal, petroleum and natural gas are formed due to the burial, of large plants and ancient creatures whose ultimate source of energy is the sun.

Renewable sources ofenergy: They are indirectly derived from solar energy such as:

Energy from flowing water: Clouds are formed when water in lakes, rivers, seas,
etc., evaporates due to solar energy. They bring rainfall and snowfall. The rain
and melting snow feed rivers, streams, etc. This flowing water can be used for
getting hydroelectricity.

Wind energy: Wind energy arises due to uneven heating ofthe earth’s surface by the sun’s rays at two different adjoining places. Due to this, a pressure difference is created and wind possesses kinetic energy.

Bio-energy: Plants in the process of photosynthesis convert solar energy into food (chemical energy). This food is consumed by animals. Thus, the animal’s wastes and remains of the plants constitute biomass which can be utilised as a source of energy.

Wave energy: The waves are generated by strong winds (due to solar energy)
blov/ing across the sea.

Ocean thermal energy: The Sun is responsible for the temperature difference between
the water at the surface and water at depth in seas and oceans.

Solar heating devices: They derive their energy directly from solar energy and convert it into other usable forms of energy. Thus, the energy from various sources is considered to have been derived from the sun.

Question 18. What is biomass? Explain the principle and workings of a biogas plant using a labelled schematic diagram.
Answer: Biomass refers to the organic fuel obtained from plant and animal wastes like wood, cow dung, residue after harvesting the crop, vegetable waste sewage, etc.

It has been used as a fuel for a long time. These fuels, however, do not produce much heat on burning and a lot of smoke is given out when they are burnt.

Bio-energy can be produced in a plant, known as a ‘biogas plant or gobar gas plant’ using biomass like cow dung, various plant materials like the residue after harvesting the crops, vegetable waste and sewage are decomposed in the absence of oxygen to give biogas. The labelled diagram of the ‘gobar gas’ plant is given in the figure.

Principle: It is based on the principle that the anaerobic micro-organisms decompose or breakdown complex compounds ofthe cow-dung slurry, in the absence of oxygen, in a few days and generate gases like methane, carbon dioxide, hydrogen and hydrogen sulphide which burn without smoke and leave no residue like ash.

Working: The plant has a dome-like structure built with bricks. A slurry of cow dung, various plant materials like the residue after harvesting the crops, vegetable waste, sewage and water is made in the mixing tank from where it is fed into the digester. The digester is a sealed chamber which is free from oxygen.

Anaerobic micro-organisms decompose or break down complex compounds of the cowdung slurry in a few days and generate gases like methane, carbon dioxide, hydrogen and hydrogen sulphide. The biogas is stored in the gas tank above the digester from which they are drawn through pipes for use.

Question 19. Faisal is a student of class X. He knows the principle of conservation ofenergy. One day a declamation contest was held in his school. The topic was “Energy crisis and its possible solution”.

1. Faisal was confused. He. thought when the total energy of the universe is constant then where is the question ofenergy crisis?
2. The next day he posed the same question in his science class. His science teacher was kind enough to explain the paradox.
3. What do you mean by the term ‘energy crisis’?
4. Why do we talk about the energy crisis despite the law of conservation of energy?
5. What characteristic was exhibited by Faisal?

Answer: We generally use fossil fuels like coal, petroleum, CNG gas etc., for obtaining the energy for our daily needs. However, these fossil fuels are exhaustible (or nonrenewable) in nature.

As we use more and more quantities ofthese fossil fuels, their stock on our earth is continuously decreasing and these fuels may be exhausted soon. This situation is called “energy crisis”.

Of course, the total energy of the universe remains constant but a large part is in a form which cannot be utilised by mankind. For example, when we burn petrol/diesel, chemical energy is converted into heat energy and total energy remains constant.

Yet, this heat energy produced goes to the atmosphere and cannot be extracted for our use. That’s why we say that there is a fear of a crisis of usable energy sources.

Faisal has an analytical ability of very high order. He correlated the topic of the declamation contest with the law of science and tried to get the correct answer.

He was satisfied only when he got the correct answer to his doubts from his science teacher.

Question 20. Fossil fuels are fuels formed by natural processes such as anaerobic decomposition of buried dead organisms. The age of the organisms and their resulting fuels is typically millions of years and sometimes exceeds 650 million years.

Fossil fuels contain a high percentage of carbon and include coal, petroleum and natural gas. They range from volatile materials with low carbon hydrogen ratios like methane to liquid petroleum to nonvolatile materials compared to pure carbon like anthracite coal.

Fossil fuels produce around 21.3 billion tonnes of carbon dioxide per year whereas naturalprocesses can only absorb about half of that amount, so there is a net increase of 10.65 billion tonnes of atmospheric carbon dioxide per year.

Carbon dioxide is one ofthe greenhouse gases that enhance radiative forcing and contribute to global warming, causing the average surface temperature rise in response, which the vast majority of climate scientists agree will cause major adverse effects.

Is that the only reason that we should be cautious about using fossil fuels?

What steps would you suggest to be taken?

Answer: On the one hand the amount of available fossil fuels is decreasing and it is non-renewable sources ofenergy. Secondly burning of fossil fuels also produces many other poisonous gases like SO2, NO2, etc.

We should encourage the development of renewable sources ofenergy like solar energy,
geothermal energy, wind energy, hydroelectric energy.

Question 21. Recently when the Government decided to set up a nuclear powerplant in an area NGOs and local people raised their voices against it. They demanded that the Government should assure safety measures before setting up such a plant and the Government assured them of it.

1. Explain the value exhibited.
2. List any two concerns ofthe people for which they were demanding safety measures.

Answer: The NGOs and people did want to set up nuclear power plants for an increased supply of energy and hence growth of the country. At the same time, it was desired that all safety measures be taken to ensure a peaceful and healthy environment around our place.

1. Nuclear radiation is very harmful to the sustenance of life and plants on Earth.
2. To take proper safeguards against the leakage of the radiations.
3. To take steps for the safe arrangement of disposing of nuclear wastes.

NCERT Solutions For Class 10 Science Chapter 8 How do Organisms Reproduce

Question 1.

1. Name the human male reproductive organ that produces sperm and also secretes a hormone. Write the functions of the secreted hormone.
2. Name the parts of the human female reproductive system where:
   1. Fertilisation takes place.
   2. Implantation of the fertilised egg occurs. Explain how the embryo gets nourishment inside the mother’s body.

Answer:

1. Testes-secrete male hormone-testosterone

Functions:

1. Formation of sperms.
2. Development of secondary sexual characters.

2.

1. Fallopian tube/Oviduct.
2. Uterus.

• The placenta is a special disc-like tissue embedded in the mother’s uterine wall and connected to the foetus/embryo.
• The placenta provides a large surface area for glucose and oxygen/nutrients to pass from the mother’s blood to the embryo/foetus.

Read and Learn More Class 10 Science Solutions

Question 2. Identify A, B and C in the given diagram and write their functions.

Mention the role of gamete and zygote in sexually reproducing organisms.

Answer:

1. A Stigma, B→ Pollen tube, C→ Female gamete

Functions:

Stigma: It receives pollen.

Pollen tube: It transfers the male gamete.

Female gamete: After fertilization, a zygote is formed which develops into a new individual.

A gamete is a haploid cell which fuses to form a diploid zygote.

After fertilization, the zygote divides several times to form an embryo within the ovule. The ovule develops a tough coat and is gradually converted into a seed.

Question 3. List five distinguishing features between sexual and asexual types of reproduction in tabular form.
Answer:

Question 4. Explain what happens when:

1. Testosterone is released in males.
2. Pollen grain falls on the stigma of the flower.
3. Egg fuses with sperm cells.
4. Planaria is cut into many pieces.
5. Buds are formed on the notches of the Bryophyllum leaf.

Answer:

1. 1. Formation of sperms, change in appearance.
   2. Thick hair grows on the face and the voice begins to crack.
2. A tube grows out of the pollen grain and travels through the style to reach the ovary.
3. Zygote is formed (Fertilization).
4. Each piece grows into a complete organism.
5. Buds may fall on the soil and develop into new plants.

Question 5. Define the following processes:

1. Fertilization
2. Menstruation
3. Binary fission
4. Vegetative propagation
5. Regeneration

Answer:

1. The fusion of the male gamete with the female gamete is known as fertilization.
2. The cycle which takes place every month when the egg is not fertilized is known as menstruation.
3. It lasts for about two to eight days and during this cycle, the lining of the uterus slowly breaks and comes out through the vagina as blood and mucus.
4. The splitting of the nucleus into two daughter cells which can take place in any plane is known as binary fission. It can be seen in Amoeba.
5. When the vegetative parts of a plant like the root, stem or leaves develop into a new plant under appropriate conditions it is known as vegetative propagation.
6. When the body of an organism cuts into any number of pieces and each piece grows into a complete organism, it is known as regeneration. It can be seen in Hydra and Planaria.

Question 6.

1. Name the parts labelled as A, B, C and D in the diagram given below:
2. What is pollination? State its significance.
3. How does fertilization occur in flowers? Name the parts of the flower that develop into
4. Seed, and
5. Fruit after fertilization.

Answer:

1. Four labelling:
   1. A – Pollen grain
   2. B-Pollen tube
   3. C – Ovary
   4. D-Female germ cell
2. Definition: Transfer of pollen grains from anther to stigma.
   1. Significance: To bring about fertilization.
3. As the pollen lands on the suitable stigma, a pollen tube grows through the style carrying the male germ cell. It reaches the ovary and the male germ cell fuses with the female germ cell and thus fertilization takes place.
   1. Seed → Ovule
   2. Fruit → Ovary

Question 7.

1. Draw a sectional view of the human female reproductive system and label the part where:
   1. Eggs develop.
   2. Fertilization takes place.
   3. The fertilized egg gets implanted.
2. Describe, in brief, the changes the uterus undergoes
   1. To receive the zygote.
   2. If a zygote is not formed.

Answer:

1. Diagram:
   1. Labellings: Ovary (Eggs develop)
   2. Fallopian Tube/Oviduct (Fertilization takes place)
   3. Uterus (Fertilized egg gets implanted)
   1. The inner lining of the uterus thickens and is richly supplied with blood.
   2. The inner lining slowly breaks and comes out through the vagina as blood and mucus (menstruation).

Question 8. Write the two causes of the human population explosion. Explain with the help of suitable examples how this explosion can be checked.
Answer:

1. The declining death rates are due to improved medical facilities.
2. Desire for a male child.
3. Less awareness about birth control methods.
4. Illiteracy/poverty (any two)

Population explosion can be checked by:

1. Using contraceptive methods to avoid pregnancy.
   1. Contraceptive methods are used such as
      1. Mechanical barriers
      2. Drugs (as pills)
      3. Loop or copper-T and
      4. Surgical method.
   2. Pills change the hormonal balance and thus prevent the release of egg, hence fertilization is prevented.
2. Spreading awareness about the importance of a small family. This is because an expanding population makes it harder to improve everybody’s standard of living.

Question 9.

1. Identify the organisms A, and B and the mode of asexual reproduction exhibited by them.
2. How will an organism benefit if it reproduces through spores?
3. Mention the two asexual methods by which Hydra can reproduce. Explain briefly any one such method.

Answer:

1. 1. Bryophyllum-vegetative propagation.
   2. Plasmodium-multiple fission.
2. Spores are covered with thick walls that protect them until they come into contact with a moist surface.
3. Budding and regeneration.

Budding: A bud develops as an outgrowth due to repeated cell division at a specific site, these buds develop into tiny individuals, mature and detach from the parents to become new individuals.

Regeneration: Specialized cells divide to form a large number of cells and undergo changes to become various cell types and tissues.

Question 10. Explain the budding mode of asexual reproduction.
Answer:

Budding: Budding is the forming of offspring from an outgrowth or bud of a parent. The bud may be unicellular or multicellular depending upon the nature of the parent individual.

In coelenterates, tunicates and other multicellular animals it consists of a small number of cells surrounded by an epithelium. Hydra is usually formed in the lower half of the body.

The buds separate from the parent soon after their formation or after some initial growth. In many cases, individuals developed from them do not separate but remain interconnected to form a colony.

Question 11. Describe the structure of a typical flower.
Answer:

Flower is a modified shoot. It is attached to the stem by a stalk called a pedicel. The swollen tip of the pedicel is called the thalamus.

• On the thalamus are arranged four whorls of floral leaves. The outermost whorl is called calyx which is formed of green leaf-like sepals.
• The second whorl is called corolla which is coloured and formed of petals. The third whorl is called androecium which is formed of stamens. A fourth (innermost) whorl is called gynoecium or pistil and is formed of carpels.
• Stamen has two parts-filament and anther which produces grain-like structures called pollens. Stamen is the male reproductive structure of the plant. The pistil has three parts-basal ovary, long style and stigma at the top. The pistil is the female reproductive structure of the plant.

Question 12. Describe asexual reproduction in Amoeba.
Answer:

Single-celled Amoeba reproduces by the asexual method known as binary fission, i.e., during division, Amoeba splits into two halves. The splitting of the two cells during binary fission can take place in any plane.

During binary fission of amoeba, nuclear division starts first, followed by the constriction in the cell membrane. As the nuclear division completes, constriction deepens and divides into two parts, each containing one nucleus. Finally, two independent daughter amoebae are formed.

Question 13. Why are budding, fragmentation and regeneration all considered asexual types of reproduction? With neat diagrams explain the process of regeneration in Planaria.
Answer:

Budding, fragmentation and regeneration are considered asexual types of reproduction because all of them involve only one parent and gametes are not involved in reproduction. No fertilisation and then zygote formation occur in asexual reproduction.

Question 14. Write two points of difference between asexual and sexual types of reproduction. Describe why variations are observed in the offspring formed by sexual reproduction.
Answer:

During sexual reproduction, two types of gametes fuse. Although the gametes contain the same number of chromosomes, their DNA is not identical. This situation generates variations among the offspring.

Question 15. Distinguish between pollination and fertilisation. Mention the site and product of fertilisation in a flower. Draw a neat, labelled diagram of a pistil showing pollen tube growth and its entry into the ovule.
Answer:

1. The process or mechanism of transfer of pollen grains from the anther to the stigma is termed pollination.
2. The fusion of male and female gametes giving rise to a zygote is termed fertilisation.
3. The site of fertilisation is ovule.
4. The product of fertilisation is the zygote.

Question 16. Distinguish between a gamete and a zygote. Explain their roles in sexual reproduction.
Answer:

Gamete represents the sex cell or germ cell in sexual reproduction. There are two types of gametes, male and female.

• A zygote is the product of fertilisation in which a male and a female gamete fuse.
• The two fusing gametes possess characters of their parents in their DNA. Fertilisation brings the characters of both parents into one zygote cell.
• The zygote is the first cell of the next generation. It divides to form an embryo which subsequently grows into a new individual.

Question 17. Draw the diagram of a flower and label the four whorls. Write the names of gamete production organs in the flower.
Answer:

1. Male gamete forming part-anther/stamen
2. Female gamete forming part-pistil/ovary/ovule

Question 18. What is the placenta? Mention its role during pregnancy.
Answer:

The placenta is a disc-like structure in the lining of the uterine wall. It contains villi on the embryo’s side of the tissues and blood spaces on the mother’s side surrounding the villi. The embryo is connected to the placenta by a tube called the umbilical cord.

Role during pregnancy: It is through the placenta that all the requirements of the developing foetus are met.

The villi provide a large surface area that facilitates the passage of nutrition and oxygen to the embryo from the mother through blood.

Wastes produced by the embryo are removed through the placenta into the mother’s blood.

Question 19. What are various ways to avoid pregnancy? Elaborate on any one method.
Answer:

Ways to avoid pregnancy are called contraceptive methods. They include the following:

1. Mechanical barrier e.g., condom (so that sperm does not reach the egg)
2. Drugs (or pills)-change the hormonal balance so that eggs are not released.
3. Loop or copper-T prevents pregnancy.
4. Surgical method-permanent contraception.

Mechanical barrier: Several methods create a barrier between sperm and egg. Some of them are as follows:

Condoms: It is a fine rubber worn over the penis during sexual intercourse. Semen is collected in it and not discharged into the vagina. This method also prevents the spread of STDs and AIDS.

Diaphragms or caps: They can be fitted in the cervix of a woman to prevent semen from reaching the fallopian tube.

Question 20. How does fertilisation take place? Fertilisation occurs once a month. Comment.
Answer:

Fertilisation in human beings: The sperm made in the testis of males are introduced into the vagina of the woman through the penis during copulation or mating.

• The sperms are highly active and mobile and thus move up through the cervix into the uterus. From the uterus, sperm pass into the oviducts. The oviduct contains an ovum released by the ovary during ovulation.
• Millions of sperm are released into the vagina at one time, but only one sperm fuses with the ovum in the oviduct to form a zygote. This is called fertilisation.
• Fertilisation can occur only once a month because the ovary releases just one mature egg every month during a menstrual cycle (around the 14th day).

Question 21. Reproduction is essentially a phenomenon that is not for the survival of an individual but for the stability of a species. Justify.
Answer:

All living organisms need energy for their survival and growth. This energy is obtained from various life processes such as nutrition and respiration. Thus, these phenomena are essential for the living of an individual.

• Compared to these life processes, reproduction may appear to be a waste of energy as it is not essential for the survival of an individual. But it is an important function of a living being as it helps in the production of new individuals of its kind. Continuity of life has been possible through reproduction.
• Genetic material is transferred from one generation to the next by DNA copying as a result of reproduction. DNA copying takes place with high constancy and considerable variations.
• This is advantageous for maintaining features that allow the organism to survive in the changing environment. Therefore, reproduction is related to the stability of a species and is not essential for the survival of an individual.

Question 22. Describe sexually transmitted diseases and mention the ways to prevent them.
Answer:

Sexually Transmitted Diseases (STDs) are infectious diseases that are transmitted during sexual intercourse. These include bacterial infections such as gonorrhoea and syphilis, and viral infections such as warts and HIV-AIDS. To prevent STDs, the following precautions can be taken:

1. Use a protective covering called a condom, over the penis during sex.
2. Avoid multiple sex partners and maintain personal hygiene.