Class 8 Science

Class 8 Science Chapter 12 Some Natural Phenomena Very Short Answer Type Questions

Question 1. If an object is touched with the metal top of an electroscope its aluminium leaves diverge, then what conclusion do we get from this observation?
Answer: We conclude from this observation that the object has an electric charge on it.

NCERT Solutions for Some Natural Phenomena VSAQs Class 8

Question 2. How does earthing help to protect buildings?
Answer: Earthing helps to transfer unwanted electric charges in electrical circuits to flow to earth, and in such a way, it prevents electrical equipment from damage.

Some Natural Phenomena Class 8 VSAQs and Answers

Question 3. Briefly explain what the people thought the cause of lightning was in ancient times.
Answer: In ancient times, people were scared of lightning and thought that the wrath of God was visiting them. 

Question 4. During a thunderstorm, when we are in an open place nearby from home, where should we take shelter?
Answer: We should take shelter under a small tree

NCERT Solutions for Class 8 Science Some Natural Phenomena VSAQs

Question 5. To protect the building from lightning, briefly mention the place where the lightning rod should be attached.
Answer: The lightning rod should be attached to the top of the building.

NCERT Solutions For Class 8 Science Chapter 12 Some Natural Phenomena Short Answer Questions

Question 1. If scientists know so much about earthquakes, can they also predict when and where the next one will strike?
Answer: No, it is not yet possible to predict when and where the next earthquake might occur because they cause disturbance in the Earth’s crust.

NCERT Solutions for Some Natural Phenomena SAQs Class 8

Question 2. Which of the following cannot be charged easily by friction?

1. A plastic scale
2. A copper rod
3. An inflated balloon
4. A woollen cloth

Answer: 2. As copper is a conductor, when rubbing it, the charges start flowing across the length of the copper rod, which constitutes an electric current. So, copper cannot be charged easily by friction.

Question 3. When a glass rod is rubbed with a piece of silk cloth, the rod

1. And the cloth both acquire a positive charge
2. Becomes positively charged, while the cloth has a negative charge
3. And the cloth both acquires a negative charge
4. Becomes negatively charged, while the cloth has a positive charge

Answer: 2. Becomes positively charged, while the cloth has a negative charge.

NCERT Solutions for Class 8 Science Some Natural Phenomena SAQs

Question 4. Write True and F against False against the Statements

1. Like charges attract each other.
2. A charged glass rod attracts a charged plastic straw.
3. The lightning conductor cannot protect a building from lightning.
4. Earthquakes can be predicted in advance.

Answer:

1. F, as like charges repel each other and unlike charges attract each other.
2. T, but it may also repel if charges are similar.
3. F, as a lightning conductor, can protect a building from lightning.
4. F, as it is not possible to predict the occurrence of earthquakes.

Question 5. Sometimes, a crackling sound is heard while taking off a sweater during winter. Explain.
Answer: The crackling sound heard while taking off a sweater during winters is due to the rubbing of two objects, i.e. body and the wool. The rubbing of the static charges produces lightning or a spark in our clothes that produces a crackling sound. The electric charges produced by rubbing are called static charges.

NCERT Solutions for Some Natural Phenomena Chapter 12 SAQs

Question 6. Explain why a charged body loses its charge if we touch it with our hand.
Answer: When we touch a charged body, it loses its charge due to the process of earthing. As our body is a good conductor of electricity, and transfers the charge to the earth.

Question 7. Name the scale on which the destructive energy of an earthquake is measured. An earthquake measures 3 on this scale. Would it be recorded by a seismograph? Is it likely to cause much damage?
Answer: Destructive energy of an earthquake is measured on the Richter scale. Yes, the earthquake will be recorded by a seismograph in the form of seismic waves. The earthquake measuring 3 on the Richter scale cannot cause much damage.

Some Natural Phenomena Class 8 NCERT SAQs

Question 8. Suggest three measures to protect ourselves from lightning.
Answer: Lightning is an electric spark on a huge scale, which is caused by the accumulation of charges in clouds.

1. Some Measures to protect ourselves from lightning are as follows
2. We should stay under a covered area or inside the room.
3. We should not take a bath during lightning.
4. We should not use the TV, phone, or computers during lightning.

Question 9. Explain why a charged balloon is repelled by another charged balloon, whereas an uncharged balloon is attracted by another charged balloon.
Answer: Since both balloons acquire the same charges when being charged upon rubbing. Thus, they repel each other. On the other hand, one charged and the other uncharged balloon attract each other.

This is due to the property of charges that unlike charges attract each other.

The uncharged balloon, having the opposite charge, is attracted by the other charged balloon.

Question 10. List three states in India where earthquakes are more likely to strike.
Answer: Some earthquake-prone states of India are as follows

1. Kashmir
2. Gujarat
3. Rajasthan

Some Natural Phenomena SAQs NCERT Solutions Class 8

Question 11. Suppose you are outside your home and an earthquake strikes. What precautions would you take to protect yourself?
Answer: The precautions are as follows

1. We should move to an open space where trees and buildings are not available.
2. If we are driving, we should not come out. We should slow down the vehicle and move slowly away from that area to a safe spot.

Question 12. The weather department has predicted that a thunderstorm is likely to occur on a certain day. Suppose you have to go out on that day. Would you carry an umbrella? Explain.
Answer: Carrying an umbrella is not advisable during a thunderstorm. The rod of the umbrella and its supporting wires are made up of metal. Thus, during a thunderstorm, the conducting objects should be avoided.

NCERT Solutions For Class 8 Science Chapter 12 Some Natural Phenomena Long Answer Questions

Some Natural Phenomena Class 8 NCERT LAQs

Question 1. If the metal clip used in the electroscope is replaced by an ebonite rod, and a charged body is brought in contact with it, will there be any effect on the aluminium strips? Explain.
Answer: The ebonite rod acquires charge when rubbed. So, the charge transfer will be either too less or there will be no transfer of charges, so the strips of aluminium will not diverge and we will not be able to predict the object whether it is charged or not.

NCERT Solutions for Some Natural Phenomena LAQs Class 8

Question 2. Explain how lightning takes place.
Answer: Clouds having water droplets, coming from different directions, strike each other and due to striking, a friction force is created when they rub each other, and during rubbing, the charges appear on clouds (static charges).

They grow in number due to continuous charging and finally discharge when any region of moisture is found on the earth because they get a path of discharge to this place.

Question 3. Explain why It Is safer to use a wireless telephone instead of a landline telephone during lightning.
Answer: It nis ot safer to use a wired telephone during lightning because at that time lightning can enter the wire of the telephone, if it is open somewhere, that is, if there is any cut in the wire. On the other hand, there cannot be any possibility of this type in a wireless telephone.

NCERT Solutions for Class 8 Science Some Natural Phenomena LAQs

Question 4. During lightning, if you are outside the house, what precautions would you take?
Answer: Precautions during lightning while we are outside are as follows

1. Do not stand underneath a natural lightning rod, such as a tall and isolated tree.
2. Stand from any fountain or any water body.
3. Get away from tractors and other metal types of equipment like wire fences, metal pipes, rails, and another metallic paths.

Question 5. Priya went to school with an umbrella during the rainy season. One day, while returning from school, the rain started on the way. Priya opened her umbrella and saved herself from the rain.

After some time, she observed some lightning sparks in the sky. Suddenly, she folded her umbrella and went to a shelter under a closed building.

1. State the cause of lightning.
2. Priya folded her umbrella. Explain why?
   
3. Mention the method opted for by Priya here.

Answer:

1. In the clouds, the accumulation of charges causes lightning.
2. As we know that the top end of stretched umbrella is a metal part. Since, the metal is a good conductor of electricity, so if lightning strikes to the ground, then it can take the path towards umbrella. Therefore, to avoid herself from danger, Priya folded the umbrella and went to a closed building.
3. The immediate response and the scientific method are opted for by Priya here.

NCERT Solutions for Some Natural Phenomena Chapter 12 LAQs

Question 6. Mention the names of those regions of the Earth that are more prone to earthquakes.
Answer: Earthquakes are usually caused by the movement of plates on the outer layer ofearth. So, the regions which fall on the boundaries of these plates are called danger zones. In India, the most dangerous zones which are prone to earthquakes are Kashmir, western and central himalyas, the whole of North-East, Rann of Kutch, Rajasthan and the lndo-Gangetic plains.

NCERT Solution For Class 8 Science Chapter 12 Some Natural Phenomena Multiple Choice Questions

Question 1. An electroscope is a device that is used to find if an Object is

1. Charged
2. Magnetic
3. Free Of Cracks
4. Hot

Answer: 1. Charged

NCERT Solutions for Some Natural Phenomena MCQs Class 8

Question 2. Lightning conductor

1. Destroys The Building
2. Protects The Building
3. Does Not Affect The Building
4. None Of The Above

Answer: 2. Protects The Building

Question 3. Where is the lightning rod attached to protect the building from lightning?

1. On top of the building
2. In the middle of building
3. On the bottom of the building
4. All of the above

Answer: 1. On top of the building

Question 4. Which of the following is not likely to cause a tsunami?

1. A major nuclear explosion under the sea
2. Earthquake
3. Volcanic eruption
4. Lightning

Answer: 4. Lightning

NCERT Solutions for Class 8 Science Some Natural Phenomena MCQs

Question 5. The movement of the Earth’s plates causes

1. Cyclones
2. Lightning
3. Earthquake
4. Thunderstorms

Answer: 3. Earthquake

Question 6. The Earth’s plate is responsible for causing earthquakes.

1. The Crust Of The Earth
2. The Mantle Of The Earth
3. The Inner Core Of The Earth
4. The Outer Core Of The Earth

Answer: 4. The Outer Core Of The Earth

Question 7. Consider the list of terms given below

1. Competency
2. Seismic
3. Mantle
4. Fault zone
5. Inner core

NCERT Solutions for Some Natural Phenomena Chapter 12 MCQs

Question 8. The boundaries of the Earth’s plate are known as

1. 1 and 2
2. 1 and 3
3. 3 and 4
4. 2, 3, and 4

Answer: 2. 1 and 3

Question 9. The waves produced on the Earth’s surface are called

1. Radio Waves
2. Longitudinal Waves
3. Microwaves
4. Seismic Waves

Answer: 4. Seismic Waves

NCERT Class 8 Science Chapter 12 Some Natural Phenomena MCQs

Question 10. Tsunami means

1. Earthquake
2. Flood
3. Earthquake Under Sea
4. Eruption

Answer: 3. Earthquake Under Sea

Question 11. The outermost layer of the Earth is called the Competency

1. Mantle
2. Outer Core
3. Crust
4. Inner Core

Answer: 3. Crust

Some Natural Phenomena Class 8 NCERT MCQs

Question 12. Major earthquakes are less likely to occur in

1. North East India
2. rajasthan
3. rann of kutch
4. Orissa

Answer: 4. Orissa

Some Natural Phenomena MCQs NCERT Solutions Class 8

Question 13. Which instruments are used to measure earthquakes?

1. Polygraph
2. Seismography
3. Biometer
4. Thermometer

Answer: 2. Seismography

NCERT Solutions For Class 8 Science Chapter 4 Combustion And Flame Multiple Choice Questions

Question 1. Bunsen burner contains a gas X which burns with a blue flame. What is the reason behind the blue coloured flame?

1. Complete combustion of gas X
2. Presence of impurities in the gas
3. Low temperature of the flame
4. Incomplete combustion of gas X

Answer: 1. Carbon dioxide

Question 2. Unburnt carbon particles are present in the

1. Luminous flame
2. Non-luminous flame
3. Dark flame
4. Flickering flame

Answer: 1. Luminous flame

NCERT Solutions for Combustion and Flame MCQs Class 8

Question 3. Which is the hottest zone in a candle flame?

1. Blue zone
2. Yellow zone
3. Dark zone
4. Grey zone

Answer: 1. Blue zone

Question 4. What is the main product of the incomplete combustion of coal?

1. Carbon dioxide
2. Oxygen
3. Water vapour
4. Nitrogen dioxide

Answer: 1. Carbon dioxide

NCERT Solutions for Class 8 Science Combustion and Flame MCQs

Question 5. The calorific value of a fuel is expressed in a unit called

1. kilojoule per litre
2. kilojoule per milliliter
3. kilojoule per gram
4. kilojoule per kilogram

Answer: 4. kilojoule per kilogram

Question 6. Which one among the following is considered the cleanest fuel?

1. Cowdung cake
2. Petrol
3. Kerosen
4. Hydrogen gas

Answer: 4. Hydrogen gas

NCERT Solutions for Combustion and Flame Chapter 4 MCQs

Question 7. In villages, people use wood as fuel because

1. It is considered to be an ideal fuel
2. Of its easy availability and low cost
3. It is environmentally friendly
4. It catches fire easily

Answer: 2. Of its easy availability and low cost

Question 8. Shyam was cooking potato curry on a chulha. To his surprise, he observed that the copper vessel was getting blackened from the outside. It may

1. Proper combustion of fuel
2. Improperly cooked potato curry
3. Improper combustion of the fuel
4. Burning of a copper vessel

Answer: 3. Improper combustion of the fuel

Question 9. Which one of the following has the highest calorific value?

1. Kerosene
2. Biogas
3. LPG
4. Petrol

Answer: 3. LPG

Combustion and Flame Class 8 NCERT MCQs

Question 10. Our beautiful Taj Mahal is suffering from ‘marble cancer’. Acid rain reacts with marble and limestone to form calcium sulfate. It causes damage to big sculptures and marble constructions. Identify the gases that contribute to the formation of acid rain.

1. Nitrogen oxides and carbon oxides
2. Carbon dioxide and carbon monoxide
3. Sulphur oxides and carbon oxides
4. Nitrogen oxides and sulphur oxides

Answer: 4. Nitrogen oxides and sulphur oxides

Question 11. Which of the following cases is an example of spontaneous combustion?

1. Lighting a gas store
2. A car engine starting
3. A pile of dry leaves catching fire in summer
4. A chemical reaction in the laboratory

Answer: 3. Carbon dioxide

Combustion and Flame Class 8 MCQs and Answers

Question 12. Which type of combustion is characterised by a lack of oxygen during the burning process?

1. Spontaneous combustion
2. Incomplete combustion
3. Rapid combustion
4. Controlled combustion

Answer: 2. Incomplete combustion

Question 13. What is the minimum temperature at which a substance catches fire and burns on its own?

1. Boiling point
2. Melting point
3. Ignition temperature
4. Freezing point

Answer: 3. Ignition temperature

NCERT Chapter 4 Combustion and Flame MCQs Class 8

Question 14. Which of the following fire extinguishers is suitable for tackling electrical fires?

1. Water fire extinguisher
2. Foam fire extinguisher
3. Carbon dioxide fire extinguisher
4. Powder fire extinguisher

Answer: 3. Carbon dioxide fire extinguisher

NCERT Solutions For Class 8 Science Chapter 11 Chemical Effects Of Electric Current Multiple Choice Questions

Question 1. An electric current can produce

1. Heating Effect
2. Chemical Effect
3. Magnetic Effect
4. Chemical, Heating, And Magnetic Effects

Answer: 4. Chemical, Heating, And Magnetic Effects

Question 2. When an electric current is passed through a conductor solution, there is a change in colour of the solution. This indicates

1. The Chemical Effect of Current
2. The Heating Effect Of Current
3. The Magnetic Effect Of Current
4. The Lightning Effect Of Current

Answer: 1. The Chemical Effect of Current

NCERT Class 8 Science Chapter 11 Chemical Effects of Electric Current MCQs

Question 3. Tia used four different objects to fill the gap in an electric circuit, separately. The table shows what she found.

1. Which of these best conducts electricity?

1. Wood
2. Plastic
3. Copper
4. Graphic

Answer: 3. Copper

NCERT Solutions for Chemical Effects of Electric Current Chapter 11

2. Which of these is a chemical effect of electric current?

1. Glowing of the bulb
2. Heating of water
3. Ringing of a mobile phone
4. Chromium plating on iron.

Answer: 4. Chromium plating on iron

3. Which of these is a correct pair of an insulator and a conductor?

Answer: D

Question 4. Which of the following metals is used in electroplating to 5 make an object shinier and attractive?

1. Graphite
2. Zinc
3. Chromium
4. Iron

Answer: 2. Zinc

Chemical Effects of Electric Current MCQs Class 8 NCERT Solutions

Question 5. The object to be electroplated is taken as

1. Cathode
2. Anode
3. Both Can Be Taken
4. None Of These

Answer: 2. 1. Cathode

Question 6. Water can be dissociated into its components by the process of

1. Electroplating
2. Electrolysis
3. Evaporation
4. All Of These

Answer: 2. Electrolysis

NCERT Solutions For Class 8 Science Chapter 11 Chemical Effects Of Electric Current LAQs

Question 1. In the circuit given in the figure, Boojho observed that copper is deposited on the electrode connected to the negative terminal of the battery. Paheli tried to repeat the same experiment, but she could find only one copper plate. Therefore, she took a carbon rod as the negative electrode. Will copper still be deposited on the carbon rod? Explain your answer.

Answer: Copper will not be deposited on the carbon rod because, carbon rod is a poor conductor of electricity. For electroplating, the circuit must be completed, and that can be completed only by using the conducting material. Instead of a carbon rod, it should be any metal, then only it can be electroplated.

NCERT Class 8 Science Chapter 11 Chemical Effects of Electric Current LAQs

Question 2. Observe the circuit given in the figure

Boojho set up this circuit for the purification of copper. What will be the nature of (a) plate A, (b) plate B (c) the solution? Explain the process of purification.

Answer:

We take CuS04 solution and dip a pure copper plate as the cathode (-ve) and an impure copper plate as the anode (+ve). Due to the voltage of the battery, the impurities from the impure sample slowly deposit at the bottom, and the copper plate becomes purified.

NCERT Solutions for Chemical Effects of Electric Current Chapter 11

Question 3. The process that you saw in Activity 7 is used for the purification of copper. A thin plate of pure copper and a thick rod of impure copper are used as electrodes. Copper from the impure rod is sought to be transferred to the thin copper plate. Which electrode should be attached to the positive terminal of the
battery and why?
Answer:

The impure rod of copper should be attached to ihe positive terminal of the battery and pure copper plate should be attached to the negative terminal of the battery.

When electric current is passed through the copper sulphate solution, copper sulphate dissociates into copper and sulphate ions The free copper gets drawn to the electrode connected with negative terminal of the battery and starts depositing on it.

From the other electrode, a thick rod of impure copper, an equal amount of copper gets dissolved into the solution. Hence, the loss of copper from the solution is restored and the process continues. Thus, copper gets transferred from one electrode to the other.

NCERT Solutions For Class 8 Science Chapter 11 Chemical Effects Of Electric Current SAQs

Question 1. Explain in brief the procedure of glowing of bulb in a liquid.
Answer:

If the liquid between the two ends ofa tester allows the electric current to pass, then the circuit of the tester becomes complete.

The current flows in the circuit, and the bulb glows. When the liquid does not allow the electric current to pass, the circuit of the tester is not complete, and the bulb does not glow.

NCERT Class 8 Science Chapter 11 Chemical Effects of Electric Current SAQs

Question 2. State the reason why we need a magnetic compass to test the conduction of electric current.
Answer:

Sometimes the bulb does not glow on passing electric current. This is because the electric current flowing through a conductor is so small So in case ofsmall current, we need magnetic compass to test the conduction.

Question 3. Observe the figure.

image-

Which of these two circuits A or B shows the correct observation? It is not clear from the diagram that what u A and B. So. cannot predict the actual solution. But if wr compare with activity. this seems to be a potato and correct diagram is A because positive terminal makes the green spot on the potato.

Question 4. Explain how we can purify the impure metals.
Answer:

By an electrolysis process, we use a thick rod of impure metal as an anode and a thin strip of pure metal as a cathode. A water-soluble salt ofthe metal is taken as electrolyte.

On passing electric current, the metal dissolves from the impure anode and goes into electrolyte solution which is then deposited on the cathode in pure form.

Question 5. We should throw the conducting materials used in electroplating far away from residential areas. Explain why?
Answer:

As the conducting solutions or electrolytes contain various types of sites which may be poisonous and also usually addie in nature.

So, in electroplating factories. the disposal ofused conducting materials is a major problem and it should be disposed offin a proper way far away from the human population.

NCERT Solutions for Chemical Effects of Electric Current Chapter 11

Question 6. State some advantages of electroplating.
Answer: The advantages of electroplating are given below

1. It protects the metal from corrosion and rusting.
2. It is used to coat desired metals on other objects.
3. It can make more reactive metals like iron.
4. Coating of chromium on the metal gives luster to the objects.

Question 7. Paheli wants to deposit silver on an iron spoon. She took silver nitrate (AgNO.) solution in a beaker and set up a simple circuit for electroplating. Which terminal of the battery should the spoon be connected to? What material should the other electrode be made of
Answer:

The spoon should be connected to the negative terminal of the battery. The other electrode should be of silver, so that silver ions get deposited on an iron spoon.

Question 8. In case of a fire, before the firemen use the water hoses, they shut off the main electrical supply for the area. Explain why they do this.
Answer:

Since tap water is a very good conductor of electricity. So, if the main electrical supply remains ON, it can be fatal to human life because it can lead to electrocution due to water.

Question 9. A child staying in a coastal region tests the drinking water and also the seawater with his tester. He finds that the compass needle deflects more in the case of seawater. Can you explain the reason?
Answer:

As we know that the current produces the magnetic effect and causes the deflection in a magnetic needle. In the case of seawater, the salt content is much higher than that of drinking water. Thus, it produces more current than drinking water.

Therefore, as a result, the deflection in the magnetic needle It is more in the case of seawater rather than drinking water.

Chemical Effects of Electric Current SAQs Class 8 NCERT Solutions

Question 10. Is it safe for the electrician to carry out electrical repairs outdoors during a heavy downpour? Explain.
Answer:

No, it is not safe for the electrician to carry out electrical repairs outdoors during heavy downpour. Because rainwater is a good conductor of electricity. So, during heavy downpour, there is a huge risk ofelectrocution.

Question 11. Paheli had heard that rainwater is as good as distilled water. So, she collected some rainwater in a clean glass tumbler and tested it using a tester. To her surprise, she found that the compass needle showed deflection. What could be the reasons?
Answer:

While it rains, the raindrops get mixed with the suspended particles of the air. So, they do not remain pure. It becomes a mixture of salts and other impurities. Thus, it shows the conduction of electricity.

But in case of distilled water, no conduction of electricity takes place as distilled water do not contain salts or impurities. Thus, it becomes a bad conductor of electricity.

Question 12. Prepare a list of objects around you that are electroplated.
Answer:

List of objects that are electroplated arc as follows;

1. Bath taps, kitchen gas burners,
2. Jewellery makers electroplate silver and gold on less expensive metals.
3. Electroplating iron cans with tin to store food.
4. Handlebars, bar cycles, and motorcycles.
5. Rims of cycles, buckles of clothes, and belts,

Question 13. Explain how we can purify the impure metals.
Answer:

By an electrolysis process, we use a thick rod of impure metal as an anode and a thin strip of pure metal as a cathode. A voter soluble salt ofthe metal is taken as electrolyte.

On passing electric current, the metal dissolves from the impure anode and goes into electrolyte solution which is then deposited on the cathode in pure form.

SAQs for Chemical Effects of Electric Current Chapter 11 Class 8

Question 14. We should throw away the conducting materials used in electroplating far away from residential areas. Explain why?
Answer:

As the conducting solutions or electrolytes contain various types of salts, which may be poisonous, and also usually addictive.

So, in electroplating factories. the disposal ofused conducting materials is a major problem and it should be disposed offin a proper way far away from the human population.

Question 15. State some advantages of electroplating.
Answer:

The advantages of electroplating are given below

1. It protects the metal from corrosion and rusting.
2. It is used to coat desired metals on other objects.
3. It can make more reactive metals like iron.
4. Coating of chromium on the metal gives luster to the objects.

Question 16. Paheli wants to deposit silver on an iron spoon. She took silver nitrate (AgNO.) solution in a beaker and set up a simple circuit for electroplating. Which terminal of the battery should the spoon be connected to? What material should the other electrode be made of
Answer:

The spoon should be connected to the negative terminal of the battery. The other electrode should be of silver, so that silver ions get deposited on an iron spoon.

Question 17. Last Monday, Ankush woke up late in the morning. So, he saw the time and suddenly realised that he had got late for an interview, which he was supposed to give after reaching the venue by the right time.

Immediately, he turned ON the geyser, but it did not work. He got more tense, then he used an electric iron rod through which he could get some boiled water for his bath.

There was an earthing problem in the switchboard, which he was unaware of.

He was barefoot and was just about to switch ON the electric iron rod, but at the same he was stopped from doing so by one of his room partner living with him. It could be dangerous for Ankush.

1. Explain in brief that what could be happened with Ankush. if he switched ON the electric iron rod (without wearing any slippers in his foot).
2. Mention the values shown by Ankush’s friend.

Answer:

If Ankush switched ON the electric iron rod and (without wearing any footwear), then he could have met with some accident, either in the form of electrical sparking or short circuit of the switchboard.

Ankush’s friend seems to be very intelligent and very much concerned for Ankush as well.

NCERT Solutions for SAQs on Chemical Effects of Electric Current

Question 18. Explain in brief the procedure for glowing of the bulb in a liquid.
Answer:

If the liquid between the two ends of a tester allows the electric current to pass, then the circuit of the tester becomes complete.

The current flows in the circuit and the bulb glows. When the liquid does not allow the electric current to pass, the circuit of the tester is not complete, and the bulb does not glow.

Question 19. State the reason why we need a magnetic compass to test the conduction of electric current.
Answer:

Sometimes the bulb does not glow on passing electric current. This is because the electric current flowing through a conductor is so small So in case of small current, we need magnetic compass to test the conduction.

NCERT Solutions For Class 8 Science Chapter 11 Chemical Effects Of Electric Current VSAQs

Question 1. It is dangerous to touch an electrical appliance with wet hands. Explain why?
Answer: A Wet hand acts as a good conductor. So, we feel an electric shock when we touch an electrical appliance with wet hands.

Question 2. Paheli and Boojho want to remind you that one should not experiment with the electric supply from the mains or a generator or an inverter. Why ?
Answer: The electrical supply which comes in our domestic main electrical line is about 120 V. We should not use this High voltage electricity for an experiment. This can cause serious injuries or instant death.

NCERT Class 8 Science Chapter 11 Chemical Effects of Electric Current VSAQs

Question 3. Sometimes we see that the liquid is conducting, but the bulb may not glow. Why?
Answer: The bulb does not glow because the current through it is too weak

Question 4. The bulb glows when the electric current passes through it. Explain why?
Answer: Due to the heating effect of the current, the filament of the bulb gets heated to a high temperature, and it starts glowing. However, if the current through a circuit is too weak, the filament does not get heated sufficiently, and it does not glow.

Question 5. When a compass needle is brought near a current-carrying wire, what happens?
Answer: When a compass needle is brought near a current-carrying wire, the needle deflects.

Question 6. Can we make another tester v/hich can detect a weak current?
Answer: Yes. we can use another effect of an electric current to make another kind of tester, i.e. magnetic effect of electric current.

Question 7. Do poor conductors also allow electricity to pass under certain conditions?
Answer: Yes, poor conductors can conduct electricity under certain conditions, like wet wood.

NCERT Solutions for Chemical Effects of Electric Current Chapter 11

Question 8. Give the names of these substances, which, when added to distilled water, make them good conductors of electricity
Answer: Acids, bases, and salts are those substances that, when added to distilled water, make it a good conductor of electricity.

Question 9. Give the names of the three effects of electric current.
Answer: The three effects of electric current are

1. The heating effect of the current
2. Magnetic effect of current
3. Chemical effect of the current

Question 10. An electric current is passed through a conducting solution. List any three possible observations.
Answer: Three possible observations are

1. The colour of the solution may change depending on the electrodes.
2. The temperature of the solution may increase.
3. Bubbles near the electrodes can be seen.

Class 8 Chapter 11 Chemical Effects of Electric Current VSAQs

Question 11. After doing the electroplating activity, Paheli interchanged the electrodes and repeated the activity. What do you think she would observe this time?
Answer: Paheli will observe the gas bubbles.

Question 12. In the electroplating process, what about the loss of copper from the solution?
Answer: An equal amount of copper gets dissolved in the solution from anode, thus the loss ofcopper from the solution is restored.

Question 13. The process of depositing a layer of any desired metal on another material employing electricity is called
Answer: Electroplating

Question 14. When the free ends of n tester arcs are dipped into solutions, the magnetic needle shows deflection. Can you explain the reason?
Answer: When the free ends of a tester arc are dipped into a solution, the liquid between the two ends allows the electric current to pass, and the circuit of the tester becomes complete.

Also, when the current passes through the tester, it establishes a magnetic effect, and hence, the magnetic needle shows deflection. In other words, we can say that the solution is a good conductor ofelectricity, so the needle gets deflected.

NCERT Solutions For Class 8 Science Chapter 10 Sound Multiple Choice Questions

Question 1. The ultrasound waves can penetrate matter to a large extent because they have

1. Very High Frequency
2. Very High Speed
3. Very High Quality
4. Very High Amplitude

Answer: 1. Very High Frequency

Question 2. A person works in a factory where a lot of industrial machines run daily. What harmful effects is he likely to suffer from?

1. Fever
2. Cataract
3. Lack of vision
4. Lack of hearing

Answer: 4. Lack of hearing

NCERT Class 8 Science Chapter 10 Sound MCQs

Question 3. Loudness of sound is measured in units of

1. Decibel (db)
2. Hertz (Hz)
3. Metre (m)
4. Metre/second(m/s)

Answer: 1. Decibel (db)

Question 4. The loudness of sound is determined by its

1. Amplitude of vibration
2. Ratio of amplitude and frequency of vibration
3. Frequency of vibration
4. Product of amplitude and frequency of vibration

Answer: 1. Amplitude of vibration

Question 5. Pitch of sound is determined by its NCERT

1. Frequency
2. Speed
3. Amplitude
4. Loudness

Answer: 1. Frequency

NCERT Solutions for Sound Chapter 10

Question 6. The maximum displacement of a vibrating body from its mean position Is called

1. Frequency
2. Period
3. Amplitude
4. None Of These

Answer: 3. Amplitude

Question 7. Ultrasound has a frequency of vibration

1. Between 20 and 20000 Hz
2. Below 20 Hz
3. Above 20000 Hz
4. Between 500 and 10000 Hz

Answer: 3. Above 20000 Hz

Question 8. Which of the following sounds can be classified as noise for humans?

1. Sounds that are softer than 20 dB
2. Sounds that are in between 20 dB and 40 dB
3. Sounds that are between 40 dB and 80 dB
4. Sounds that are louder than 80 dB

Answer: 4. Sounds that are louder than 80 dB

Class 8 Chapter 10 Sound Multiple Choice Questions

Question 9. Which of the following are used to study the growth of the foetus inside the mother’s womb?

1. Radiowaves
2. X-rays
3. Infrared waves
4. Sound waves

Answer: 4. Sound waves

Question 10. Sound can be produced by

1. Applying an object
2. Vibration on objects
3. Passing electric current through an object.
4. Effect of a magnet on an object

Answer: 2. Vibration ot objects

Question 11. Loudness of sound depends upon its

1. Frequency
2. Pitch
3. Amplitude
4. Shirillness

Answer: 3. Amplitude

NCERT Solutions for MCQs on Sound Chapter 10

Question 12. The human brain can sense sound frequencies

1. Less Than 20 Hz
2. Between 20 Hz And 20000 Hz
3. More Than 20000 Hz
4. All Of The Above

Answer: 2. Between 20 Hz And 20000 Hz