NCERT Exemplar Solutions for Class 10 Maths Chapter 12 Area Related To Circles

NCERT Exemplar Solutions for Class 10 Maths Chapter 12  Area Related To Circles

Area Related To Circles Introduction

We are familiar with the shape of a circle. The circumference of the wheels of cars, and coins appears as a circle.

A circle can be defined as “A figure with an outline, every point on this outline is at the same constant distance from a certain point inside the figure, which is called the centre”.

NCERT Exemplar Solutions for Class 10 Maths Chapter 12 Area Related To Circles

NCERT Exemplar Class 10 Maths Chapter 12

NCERT Exemplar Solutions for Class 10 Maths Chapter 12  Area Related To Circles Area And Circumference Of A Circle

Let r be the radius of the circle. The distance travelled once around a circle is its perimeter, usually called its circumference. Now

Area of circle = πr2

Circumference of circle = 2πr

Read and Learn More Class 10 Maths Solutions Exemplar

Area Related To Circles Area And Circumference Of A Circle

π(pi) is a fixed irrational number whose approximate value is \(3.1416 \text { as } \frac{22}{7} \text { or } \frac{355}{113}\) (sometimes)

Diameter: A chord of a circle passing through its centre is called the diameter of the circle.

Diameter = 2 x radius

NCERT Exemplar Solutions for Class 10 Maths Chapter 12  Area Related To Circles Formulae Of Circle

1. Area of circle = πr2
2. Circumference of a circle = 2πr

Area Related To Circles Area Of Circle

3. Area of semicircle = \(\frac{1}{2} \pi r^2\)

Area Related To Circles Area Of Semicircle

4. Perimeter of semicircle = (πr + 2r)

5. For a ring having outer radius = R and inner radius = r
Area of ring = π(R2 – r2)

Area Related To Circles Ring Having Outer Radius

6. For rotation of the hands of a clock

  1. Angle described by minute hand in 60 minutes = 360°
  2. Angle described by hour hand in 12 hours = 360°

Area Related To Circles Rotation Of The Hands Of A Clock

7. For rotating wheels

  1. Distance moved by a wheel in 1 rotation = its circumference
  2. Number of rotation in unit time = \(\frac{\text { distance moved in unit time }}{\text { circumference }}\)

Area Related To Circles Rotating Wheels

NCERT Exemplar Solutions for Class 10 Maths Chapter 12  Area Related To Circles Solved Examples

Question 1. The circumference of a field is 220 m. Find

  1. Its radius
  2. Its area.

Solution:

Circumference of circle = 220 m

2πr = 220

⇒ \(r=\frac{220 \times 7}{2 \times 22}=35 \mathrm{~m}\)

Area of circle = \(\pi r^2=\frac{22}{7} \times 35 \times 35=3850 \mathrm{~m}^2\)

Question 2. Find the area of a circular park whose radius is 4.5 m.

Solution:

Area of circular park = r2

⇒ Area = \(\text { Area }=\frac{22}{7} \times 4.5 \times 4.5\)

Area = 63.63 m2

The area of a circular park = 63.63 m2

Question 3. The area of a circular plot is 346.5 m2. Calculate the cost of fencing the plot at the rate of ₹ 6 per metre.

Solution:

Area of plot = 346.5 m2

⇒ πr2 = 346.5 m2 ⇒ \(r^2=\frac{346.5 \times 7}{22}\)

⇒ r2 = 110.25 ⇒ r = 10.5 m

Circumference of plot = \(2 \pi r=2 \times \frac{22}{7} \times 10.5=66 \mathrm{~m}\)

Cost of fencing = Circumference x Cost of fencing per metre

= ₹ 66 x 6 = ₹ 396

The cost of fencing the plot at the rate of ₹ 6 per metre = ₹ 396

Question 4. The diameter of a cycle wheel is 28 cm. How many revolutions will it make in moving 13.21cm?

Solution:

Given

The diameter of a cycle wheel is 28 cm.

Distance travelled by the wheel in one revolution = \(2 \pi r=\frac{22}{7} \times 28=88 \mathrm{~cm}\)

Total distance travelled by the wheel = 13.2 x 1000 x 100 cm

Number, of revolutions made by the wheel = \(\frac{\text { total distance }}{\text { circumference }}\)

= \(\frac{13.2 \times 1000 \times 100}{88}=15000 \text { revolutions }\)

15000 revolutions will it make in moving 13.21cm.

Question 5. The circumference of a circle exceeds the diameter by 16.8 cm. Find the radius of the circle.

Solution:

Given

The circumference of a circle exceeds the diameter by 16.8 cm.

Let the radius of the circle be r.

Diameter = 2r

Circumference of circle = 2πr

Using the given information, we have

2πr = 2r + 16.8

⇒ \(2 \times \frac{22}{7} \times r=2 r+16.8\)

⇒ 44r = 14r + 16.8 x 7

⇒ 30r = 117.6

∴ \(r=\frac{117.6}{30}=3.92 \mathrm{~cm}\)

The radius of the circle =3.92 cm

Question 6. Find the area of a ring whose outer and inner radii are respectively 20cm and 1 5cm.

Solution:

Outer radius R = 20 cm

Inner radius r = 15 cm

∴ Area of ring = π(R2 – r2)

⇒ Area of ring = \(\frac{22}{7}\left[(20)^2-(15)^2\right]=\frac{22}{7}(400-225)=\frac{22}{7} \times 175 \mathrm{~cm}^2\)

= 22 x 25 = 550 cm2.

The area of a ring = 550 cm2.

Question 7. A race track is in the form of a ring whose inner circumference is 352 m and the outer circumference is 396 m. Find the width of the track.

Solution:

Given

A race track is in the form of a ring whose inner circumference is 352 m and the outer circumference is 396 m.

Let R and r be the outer and inner radii of the circle.

The width of the track = (R – r) cm

Now, 2πr = 352 ⇒ \(2 \times \frac{22}{7} \times r=352\)

⇒ \(r=\frac{352 \times 7}{2 \times 22}=7 \times 8=56 \mathrm{~m}\)

Again, 2πR = 396 ⇒ \(2 \times \frac{22}{7} \times R=396\)

⇒ \(R=\frac{396 \times 7}{2 \times 22}=7 \times 9=63 \mathrm{~m}\)

∴ R = 63 m, r = 56 m

Width of the track = (R- r) m = (63 – 56) m = 7 m.

Area Related To Circles Outer And Inner Radii Of The Circle

Question 8. Two circles touch internally. The sum of their areas is 116π cm2 and the distance between their centres is 6 cm. Find the radii of the circles.

Solution:

Given

Two circles touch internally. The sum of their areas is 116π cm2 and the distance between their centres is 6 cm.

Let two circles with centres O’ and O having radii R and respectively touch each other at P.

It is given that OO’ = 6

R – r = 6 ⇒ R = 6 + r → (1)

Also, πR2 + πr2 = 116π (given)

π(R2 + r2) = 116π

⇒ R2 + r2= 116 → (2)

∴ From equations (1) and (2), we get

(6 + r)2 + r2 = 116

⇒ 36 + r2 + 12r + r2= 116 ⇒ 2r2 + 12r – 80 = 0

⇒ r2 + 6r – 40 = 0 = (r + 10) (r – 4) = 0

∴ r = -10 or r = 4

But the radius cannot be negative. So, we reject r = -10

∴ r = 4 cm

∴ R = 6 + 4 = 10cm [from(1)]

Hence, the radii of the two circles are 4 cm and 10 cm.

Area Related To Circles Two Circles Touch Internally

Area Related to Circles Class 10 Exemplar Solutions

Question 9. The radius of a wheel of a bus is 45 cm. Determine its speed in kilometres per hour, when its wheel makes 315 revolutions per minute.

Solution:

Given

The radius of the wheel of the bus = 45 cm

∴ Circumference of the wheel = 2ar

= \(2 \times \frac{22}{7} \times 45=\frac{1980}{7} \mathrm{~cm}\)

∴ Distance covered by the wheel in one revolution = \(\frac{1980}{7} \mathrm{~cm}\)

Distance covered by the wheel in 315 revolutions = \(315 \times \frac{1980}{7}\)

= 45 x 1 980 = 89 100 cm

= \(\frac{89100}{1000 \times 100} \mathrm{~km}=\frac{891}{1000} \mathrm{~km}\)

∴ Distance covered in 60 minutes or 1 hr =\(\frac{891}{1000} \times 60=\frac{5346}{100}=53.46 \mathrm{~km}\)

Hence, speed of bus = 53.46 km/hr

Question 10. Three semicircles each of diameter 3 cm, a circle of diameter 4.5 cm and a semicircle of radius 4.5 cm are drawn in the adjoining figure. Find the area of the shaded region.

Solution:

Given

Three semicircles each of diameter 3 cm, a circle of diameter 4.5 cm and a semicircle of radius 4.5 cm are drawn in the adjoining figure.

Required area = (area of larger semicircle with radius 4.5 cm) – (area of two smaller semicircles with radius of each \(\frac{3}{2}\) cm and a circle with radius \(\frac{4.5}{2}\) cm + (area of smaller semicircle with radius \(\frac{3}{2}\) cm)

= \(\frac{1}{2} \pi(4.5)^2-\left[2 \times \frac{1}{2} \pi\left(\frac{3}{2}\right)^2+\pi\left(\frac{4.5}{2}\right)^2\right]+\left[\frac{1}{2} \pi\left(\frac{3}{2}\right)^2\right]\)

= \(\frac{1}{2} \pi(4.5)^2-\pi\left(\frac{3}{2}\right)^2-\pi\left(\frac{4.5}{2}\right)^2+\frac{1}{2} \pi\left(\frac{3}{2}\right)^2\)

= \(\frac{1}{4} \pi\left[2 \times(4.5)^2-9-(4.5)^2+\frac{9}{2}\right]=\frac{1}{4} \pi \times 4.5[2 \times 4.5-2-4.5+1]\)

= \(\frac{1}{4} \pi \times 4.5(3.5)=\frac{1}{4} \times \frac{22}{7} \times 4.5 \times 3.5=12.375 \mathrm{~cm}^2\).

Area Related To Circles Three Semicircles

The area of the shaded region =12.375 c.

Question 11. In the adjoining figure, find the area of the shaded region. (Use π = 3.14)

Solution:

Diameter BD = \(\sqrt{6^2+8^2}=\sqrt{36+64}=\sqrt{100}=10 \mathrm{~cm}\)

Radius = \(]frac {10}{2}\) = 5 cm

Area of circle = πr2 = 3. 1 4 x 52 = 3. 14 x 25 = 78.50 cm2

Area of rectangle ABCD = 8 x 6 = 48 cm2

Hence, area of shaded region = 78.50- 48 = 30.5 cm2

Area Related To Circles Area Of Shaded Region

Question 12. A park is of the shape of a circle of diameter 7 m. It is surrounded by a path of width 0.7 m. Find the expenditure of cementing the path, if its cost is ₹ 110 per sq. m.

Solution:

Given

A park is of the shape of a circle of diameter 7 m. It is surrounded by a path of width 0.7 m

The radius of the circular park = 3.5 m

There is a path of width 0.7 m.

So, the radius of the external circle R = 3.5 + 0.7

⇒ R = 4.2 cm

Area of path = πR2 – πr2 = n(R- r) (R + r)

= \(\frac{22}{7}(4.2-3.5)(4.2+3.5)\)

= \(\frac{22}{7} \times 0.7 \times 7.7=16.94 \mathrm{~m}^2\)

Now, the cost of cementing 1 m2 of path = ₹ 110

Cost of cementing 16.94 m2 of path = ₹ ( 110 x 16.94) = ₹ 1863.40

Area Related To Circles Shape Of A Circle Of Diameter

Question 13. Find the area of the region between the two concentric circles, if the length of a chord of the outer circle just touching the inner circle at a particular point on it is 10 cm. \(Take, \pi=\frac{22}{7}\)

Solution:

Let the chord AB touch the inner circle at C and let 0 be the centre of both the circles, then

OC = r, OA = R and AB = 10 cm

Now, since OC ⊥ AB (∵ radius through the point of contact is perpendicular to the tangent)

∴ C is the mid-point of AB (∵ ⊥ drawn from the centre to the chord, bisects the chord)

⇒ \(A C=\frac{1}{2} A B=\frac{1}{2} \times 10=5 \mathrm{~cm}\)

Now, in right ΔOCA,

OA2 = OC2 +AC2 (by Pythagoras theorem)

R2 – r2 = 25 → (1)

The required area of the region between two concentric circles

= πR2 – πr2 = π(R2– r2) – 25π [from(1)]

= \(25 \times \frac{22}{7}=78.57 \mathrm{~cm}^2\)

Area Related To Circles Area Of The Region Between The Two Concentric Circles

Question 14. In the adjoining figure, CM = 5 cm, RB = 9 cm, CD ⊥ AB, O is the centre of the larger circle and K is the centre of the smaller circle. Find the area of the shaded region.

Solution:

Let the radius of the larger circle be R and the radius of the smaller circle is r.

Since, CM = 5 cm

∴ MO = R – 5

Also OB = R and RB = 9

∴ OR = R – 9

In ΔAOM,

∠1 + ∠2 = 90° → (1)

In ΔAMR,

∠2 + ∠3 = 90° (the angle in a semicircle is the right angle) → (2)

From eqs. (1) and (2), we get

∠1 + ∠2 = ∠2 + ∠3

⇒ ∠1 = ∠3

In Δs AMO and MOR

∠1 = ∠3 (just proved)

∠4 = ∠5 (each 90°)

∴ ΔAMO ~ ΔMRO (AA corollary)

∴ \(\frac{M O}{R O}=\frac{A O}{M O}\)

⇒ \(\frac{R-5}{R-9}=\frac{R}{R-5}\)

⇒ (R – 5)2 = R (R-9) = R2 + 25 – 10R = R2 – 9R

⇒ R = 25 cm

Now, 2R – 9 = 2r ⇒ 2r = 41

⇒ r = 20.5 cm

Required area = πR2 – πr2 = π(R + r) (R – r)

= \(\frac{22}{7} \times 45.5 \times 4.5 = 643.5 \mathrm{~cm}^2\)

Area Related To Circles Area Of Larger And Smaller Circles

Question 15. A square of the largest area is cut out of a circle. What % of the area of the circle is lost as trimmings?

Solution:

Let the radius of the circle be r units.

∴ Area of circle = πr2 sq. units

Let ABCD be the largest square.

∴ Length of diagonal = 2r = side √2

side = \(\frac{2 r}{\sqrt{2}}=\sqrt{2} r\)

∴ Area (square ABCD) = (side)2 = (√2r)2 = 2r2

∴ Area of circle lost by cutting out of a square of largest area = 2r2

∴ Required percentage of the area of circle lost = \(\frac{2 r^2}{\pi r^2} \times 100=\frac{200}{\pi} \%\).

Area Related To Circles A Square Of The Largest Area Is Cut Out Of A Circle

Question 16. In a circular table covering of radius 32 cm, a design (shade) is formed leaving an equilateral triangle ABC in the middle as shown in the adjacent figure. Find the area of the shaded region.

Solution:

Since ABC is an equilateral triangle.

∴ ∠A = 60°

⇒ ∠BOC = 2 x ∠BAC = 2 x 60° = 120° (degree measure of an arc is twice the angle subtended by it in an alternate segment)

Draw OM ⊥ BC

So, we can prove

ΔOMB ≅ ΔOMC (R.H.S. congruency)

∴ ∠BOM = ∠COM = 60° (c.p.c.t.)

In the right ΔOMB, we have

⇒ \(\sin 60^{\circ}=\frac{B M}{O B}\)

∴ \(\frac{\sqrt{3}}{2}=\frac{B M}{32} \quad = \quad B M=16 \sqrt{3} \mathrm{~cm}\)

∴ BC = 2 x 16√3 = 32√3 cm

∴ Area of shaded region = Area of circle- ar(AABC)

= \(\pi r^2-\frac{(\text { side })^2 \sqrt{3}}{4}=\pi \times(32)^2-(32 \sqrt{3})^2 \times \frac{\sqrt{3}}{4}\)

= \((32)^2\left(\frac{22}{7}-\frac{3 \sqrt{3}}{4}\right)=1024\left(\frac{22}{7}-\frac{3 \sqrt{3}}{4}\right) \mathrm{cm}^2\)

Area Related To Circles Equilateral Triangle

NCERT Exemplar Solutions for Class 10 Maths Chapter 12  Area Of Sector And Segment Of A Circle

Sector: The shaded region (shown in the figure) OAXB is called a sector of the circle. Its boundary consists of arc AXB and two radii OA and OB. This sector has an angle θ, subtended at the centre of the circle by the arc AXB.

The region bounded by two radii of a circle and intercepted by them is called a sector of the circle.

Area Related To Circles Area Of Sector And Segment Of A Circle

When θ < 180°, arc AB is a minor arc and when θ > 180°, arc AB is a major arc.

Now for sector AOB with ∠AOB = θ°, then the length of minor arc AB \(2 \pi r \times \frac{\theta}{360^{\circ}} \text { i.e., } \frac{\pi r \theta}{180^{\circ}}\)

(Actually, 2πr is the distance covered in travelling the whole circumference in which an angle of 360 is formed at the centre. But for the length of the arc AXB, we do not rotate 360°, here we needed only 0 part of 360°)

∴ \(l=\frac{2 \pi r \theta}{360}\)

and the area of sector is \(\pi r^2 \times \frac{\theta}{360^{\circ}}\)

∴ \(A=\frac{\pi r^2 \theta}{360^{\circ}}\)

Relation between Length of Arc and Area of Sector

Area of sector \(A=\pi r^2 \times \frac{\theta}{360^{\circ}}\)

= \(\pi r \times \frac{\theta}{360^{\circ}} \times r=\frac{1}{2} \times 2 \pi r \times \frac{\theta}{360} \times r=\frac{1}{2} l r\)

Segment of a Circle: A segment of a circle is defined as the part of a circle bounded by a chord and the circumference. The segment containing the major arc is the major segment while the segment containing the minor arc is a minor segment.

Area of minor segment = Area of the sector- an area of ΔOAB.

= \(\left(\frac{\pi r^2 \theta}{360^{\circ}}-\frac{1}{2} r^2 \sin \theta\right) \text { sq. unit }\)

Area Related To Circles Segment Of A Circle

Area of major segment = Area of circle- Area of minor segment

Perimeter of sector = \(\frac{\pi r \theta}{180^{\circ}}+2 r\)

Perimeter of minor segment = \(\frac{\pi r \theta}{180^{\circ}}\) + Length of chord AB

Area of semicircle = \(\frac{\pi r^2}{2}\)

Perimeter of semicircle = \(\pi r+2 r\)

Area of quarter circle = \(\frac{\pi r^2}{4}\)

Perimeter of quarter circle = \(\frac{\pi r}{2}+2 r\)

Area Related To Circles Area Of Major Segment

NCERT Exemplar Solutions for Chapter 12 Class 10

NCERT Exemplar Solutions for Class 10 Maths Chapter 12  Area Related To Circles Solved Questions And Answers

Question 1. The perimeter of a semi-circular protractor is 32.4 cm. Calculate:

  1. The radius of the protractor in cm,
  2. the arc of the protractor in cm2.

Solution:

Let the radius of the protractor be r cm.

Perimeter of semicircle protractor = (πr + 2r)cm

∴ r(π + 2) = 32.4

⇒ \(r\left(\frac{22}{7}+2\right)=32.4\)

⇒ \(r \times \frac{36}{7}=32.4 \quad ⇒ \quad r=\frac{32.4 \times 7}{36} ⇒ r=6.3 \mathrm{~cm}\)

Hence, the radius of the protractor = 6.3 cm

Area of semi-circular protractor = \(\frac{1}{2} \pi r^2\)

= \(\frac{1}{2} \times \frac{22}{7} \times 6.3 \times 6.3=62.37 \mathrm{~cm}^2\)

Hence, the area of the protractor = 62.37 cm2

Question 2. The minute hand of a clock is √2I cm long. Find the area described by the minute hand on the face of the clock between 6 a.m. and 6.05 a.m.

Solution:

In 60 minutes, the minute hand of a clock move through an angle of 360°.

∴ In 5 minutes hand will move through an angle = \(\frac{360^{\circ}}{60} \times 5=30^{\circ}\)

Now, r = √21 cm and θ = 30°

The area of sector described by the minute hand between 6 a.m. and 6.05 a.m.

= \(\frac{\pi r^2 \theta}{360^{\circ}}=\frac{22}{7} \times(\sqrt{21})^2 \times 30^{\circ} \times \frac{1}{360^{\circ}}=5.5 \mathrm{~cm}^2\)

Question 3. In the adjoining figure, calculate:

  1. The length of minor arc ACB
  2. Area of the shaded sector.

Solution:

Here, θ = 150°, r = 14 cm

Area Related To Circles Adjoining Triangle

1. Length of minor arc = \(\frac{\pi r \theta}{180^{\circ}}\)

= \(\frac{22}{7} \times 14 \times 150^{\circ} \times \frac{1}{360^{\circ}}\)

= 36.67 cm

2. Area of shaded sector = \(\frac{\pi r^2 \theta}{360^{\circ}}=\frac{22}{7} \times(14)^2 \times 150^{\circ} \times \frac{1}{360^{\circ}}=256.67 \mathrm{~cm}^2\)

Question 4. A chord AB of a circle of radius 10 cm makes a right angle at the centre of the circle. Find the area of the major and minor segments. (Use π = 3.14).

Solution:

Area of sector OAB = \(\frac{\pi r^2 \theta}{360^{\circ}}=3.14 \times 10^2 \times \frac{90^{\circ}}{360^{\circ}}=78.5 \mathrm{~cm}^2\)

Now, area of \(\triangle A O B=\frac{1}{2} \times(10)^2=50 \mathrm{~cm}^2\)

Area of the minor segment = (78.5 – 50) cm2 = 28.5 cm2

Area of the major segment = Area of the circle – Area of the minor segment

= (3.14 x 102 – 28.5) cm2 = (314 – 28.5) cm2 = 285.5 cm2

Area Related To Circles Area Of Major And Minor Segment

Question 5. In the adjoining figure, the side of the square is 28 cm and the radius of each circle is half of the length of the side of the square where O and O’ are the centres of the circle. Find the area of the shaded region.

Answer:

Side of square = 28 cm

and the radius of each circle = 14 cm

Required area = area of square excluding the two sectors + area of two circles

= \((28)^2-2\left[\pi(14)^2 \times \frac{90^{\circ}}{360^{\circ}}\right]+2\left[\pi(14)^2\right]\)

= \((28)^2-2 \times \frac{22}{7} \times 14 \times 14 \times \frac{1}{4}+2 \times \frac{22}{7} \times 14 \times 14\)

= 784 – 308 + 1232 = 1708 cm2

Area Related To Circles Area Of Square Excluding The Two Sectors And Two Circles

Question 6. In the adjoining figure, ABCD is a trapezium with AB || DC, AB = 18 cm, DC = 32 cm and the distance between AB and DC is 14 cm. If arcs of equal radii 7 cm taking A, B, C and D as centres, have been drawn, then find the area of the shaded region.

Solution:

Area of the shaded region

= area of trapezium – area of four sectors

= \(\begin{aligned}
\frac{1}{2} \times 14(32+18)-\left[\pi(7)^2 \times \frac{\angle A}{360^{\circ}}+\right. & \pi(7)^2 \times \frac{\angle B}{360^{\circ}} \left.+\pi(7)^2 \times \frac{\angle C}{360^{\circ}}+\pi(7)^2 \times \frac{\angle D}{360^{\circ}}\right]
\end{aligned}\)

= \(=7 \times 50-\frac{\pi \times(7)^2}{360^{\circ}}(\angle A+\angle B+\angle C+\angle D)\)

= \(=350-\frac{22}{7} \times \frac{7 \times 7}{360^{\circ}} \times 360^{\circ}\) (∵ sum of all the four angles of a quad. is 360°)

= 350 – 154 = 196 cm2

Hence, the area of the shaded region is 196 cm2.

Area Related To Circles Trapezium

Question 7. In the adjoining figure, two circular flower beds have been shown on two sides of a square lawn ABCD of side 56 m. If the centre of each circular flower bed is the point of intersection O of the diagonals of the square lawn, find the sum of areas of the lawn and the flower beds.

Solution:

We know that the diagonals of a square bisect each other perpendicularly.

∴ ∠DOC = 90°

Also diagonal BD = side √2 = 56√2m

∴ \(O D=\frac{1}{2} \times B D=28 \sqrt{2} \mathrm{~m}\)

∴ Area of \(\triangle D O C=\frac{1}{2} \times 28 \sqrt{2} \times 28 \sqrt{2}=(28)^2 m^2\)

Area of sector ODCO = \(\pi(O D)^2 \times \frac{\theta}{360^{\circ}}\)

= \(\pi(28 \sqrt{2})^2 \times \frac{90^{\circ}}{360^{\circ}}=\frac{11 \times 28 \times 28}{7} \mathrm{~m}^2\)

= 1232 m2

∴ Area of 1 flower bed = Area of sector- Area of A

= 1232 -(28)2 = 448 m2

∴ Area of 2 flowers beds = 2 x 448 = 896 m2

Area of square lawn = (56)2 = 3136 m2

∴ Required area = 896 + 3136 = 4032 m2

Area Related To Circles Two Circular Flower Beds

Question 8. In the adjoining, ABCD is a square of side 10 cm and two A semicircles with side of the square as diameter. A quarter circle is also seen with a side of the square as a radius. Find the area of the square region excluding the shaded part (Deepak).(Takeπ = 3.14)

Area Related To Circles A Square Of Semicircles With Side Of The Square As Diameter

Solution:

First of all, we will find the area of 1 and 2 i.e., Batti of Deepak, draw OM ⊥ AB and ON ⊥ BC.

ar(1) = ar(sector NBKO) – ar(ABNO)

= \(\pi(5)^2 \times \frac{90^{\circ}}{360^{\circ}}-\frac{1}{2} \times 5 \times 5\)

ar (2) = ar (1)

⇒ \(\operatorname{ar}(\mathrm{1}+\mathrm{2})=2\left(\frac{25 \pi}{4}-\frac{25}{2}\right)=\frac{25}{2}(\pi-2)\)

∴ \(\frac{25}{2}(3.14-2)=14.25 \mathrm{~cm}^2\)

Now, area of deepak = ar(quadrant APCB) – [ar(semicircle 4 + 1 + 2) + ar(semicircle 5 + 1 + 2) – 2 x ar (1 + 2)]

= \(\pi(10)^2 \times \frac{90}{360}-\left[2 \times \frac{\pi(5)^2}{2}-2 \times 14.25\right]\)

25π – (25π – 28.5) = 28.5 cm2

Area of unshaded portion = Area of the square- Area of deepak

= (10)2– 28.5 = 100 – 28.5 = 71.5 cm2

The area of the square region excluding the shaded part = 71.5 cm2

Area Related To Circles A Square Of Semicircles With Side Of The Square As Diameter.

Question 9. If the hypotenuse of an isosceles right triangle is 7√2 cm, find the area of the circle inscribed in it.

Solution:

Let AB = BC = x cm

∴ In right ΔABC, by Pythagoras theorem

x2 + y2 = (7√2)2

⇒ 2x2 = 98 = x2 = 49 ⇒ x = 7 cm

∴ ar(ABC) = ar(AOB)+ ar(BOC) + ar(COA)

⇒ \(\frac{1}{2} \times x \times x=\frac{1}{2} \times x \times r+\frac{1}{2} \times x \times r+\frac{1}{2} \times 7 \sqrt{2} \times r\)

⇒\(r=\frac{7}{2+\sqrt{2}} \times \frac{2-\sqrt{2}}{2-\sqrt{2}}=\frac{7(2-\sqrt{2})}{2}\)

⇒ \(7 \times 7=7 \times r+7 \times r+7 \sqrt{2} \times r \Rightarrow r=\frac{7}{2+\sqrt{2}}\)

Area of circle = πr2

= \(\frac{22}{7} \times \frac{49(2-\sqrt{2})^2}{4}=\frac{77}{2} \times(4+2-4 \sqrt{2})\)

= 77(3 – 2√2) cm2

The area of the circle inscribed in it = 77(3 – 2√2) cm2

Area Related To Circles Hypotenuse Of An Isosceles Right Triangle

Question 10. In the adjoining figure, two concentric circles with centre O have radii of 21 cm and 42 cm. If ∠AOB = 60°, find the area of the shaded region. (\(\text { Use } \pi=\frac{22}{7}\))

Solution:

Required area = area of a larger circle with a radius of 42 cm – an area of a smaller circle with a radius of 21 cm – (area of unshaded portion CDBA)

= π(42)2 – π(21 )2 – [(area of the larger sector with radius 42 cm) – (area of the smaller sector with radius 21 cm)]

= \(\pi(42)^2-\pi(21)^2-\left[\pi(42)^2 \times \frac{60}{360}-\pi(21)^2 \times \frac{60}{360}\right]\)

= \(\pi(42)^2-\pi(21)^2-\frac{1}{6} \pi(42)^2+\frac{1}{6} \pi(21)^2=\frac{5}{6} \pi(42)^2-\frac{5}{6} \pi(21)^2\)

= \(\frac{5}{6} \pi \times(21)^2[4-1]=\frac{5}{6} \times \frac{22}{7} \times 21 \times 21 \times 3=3465 \mathrm{~cm}^2\)

The area of the shaded region =3465 c

Area Related To Circles Two Concentric Circles

Question 11. In the adjoining figure, O is the centre of the circle with AC = 24 cm, AB = 7 cm and ∠BOD = 90°. Find the area of the shaded region.

Solution:

Since O is the centre of the circle.

∴ BC is the diameter of the circle.

∴ ∠CAB = 90° (angle in a semicircle is a right angle)

Now in right ΔACB, by Pythagoras Theorem,

BC2 = AC2 + AB2 = (24)2 + (7)2 = 576 + 49 = 625

∴ BC = = 25 m

∴ Diameter of circle = 25 m

∴ Radius of circle = \(\frac{25}{2}\) = 12.5 m

∴ OC = OD = 12.5 m (each radii)

∴ Area of shaded region = area of circle – ar (ΔABC) – ar (sector COD)

= \(\pi(12.5)^2-\frac{1}{2} \times A C \times A B-\pi(O C)^2 \times \frac{90^{\circ}}{360^{\circ}}\)

= \(\frac{22}{7} \times 12.5 \times 12.5-\frac{1}{2} \times 24 \times 7-\frac{22}{7} \times 12.5 \times 12.5 \times \frac{1}{4}\)

= 491.07 – 84 – 122.768 = 284.302 = 284.30 m2 (approx.)

The area of the shaded region = 284.30 m2 (approx.)

Area Related To Circles Centre Of The Circle

Class 10 Maths Chapter 12 Area Related to Circles

NCERT Exemplar Solutions for Class 10 Maths Chapter 12  Area Related To Circles Exercise 12.1

Question 1. The radii of the two circles are 19 cm and 9 cm respectively. Find the radius of the circle which has a circumference equal to the sum of the circumferences of the two circles.

Solution:

Here, r1 = 19 cm and r2 = 9cm

Let the radius of the new circle = R cm

Given that,

Circumference of new circle = sum of the circumference of given two circles

2πR = 2πr1 + 2πr2

R = r1 + r2 = 19 + 9 = 28 cm.

The radius of the circle = 28 cm.

Question 2. The radii of the two circles are 8 cm and 6 cm respectively. Find the radius of the circle having an area equal to the sum of the areas of the two circles.

Solution:

Here, r1 = 8 cm and r2 = 6 cm

Let the radius of the new circle = R cm

Given that,

Area of new circle = sum of areas of given circles

⇒ πR2 = πr2 + πr2

⇒ R2 = r21 + r22 = 82 + 62

= 64 + 36 = 100

⇒ R = 10 cm

The radius of the circle = 10 cm

Question 3. The depicts an archery target marked with its five scoring regions from the centre outwards as Gold, Red, Blue, Black and White. The diameter of the region representing the Gold score is 21cm and each of the other bands is 10.5 cm wide. Find the area of each of the five scoring regions.

Solution:

The diameter of the Gold circle = 21 cm

∴ Radius of Gold circle = 10.5 cm

Now, the area of the Gold Circle

= \(\frac{22}{7} \times 10.5 \times 10.5 \mathrm{~cm}^2\)

= 346.5 cm2

Given, the width of each band = 10.5 cm

∴ Radius of Red circle = (10.5 + 10.5) = 21cm

Now, area of Red ring = [(external radius)2 – (internal radius)2]

= \(\frac{22}{7}\left[(21)^2-(10.5)^2\right]\)

= \(\frac{22}{7} \times(441-110.25)\)

= \(\frac{22}{7} \times 330.75\)

= 1039.5 cm2

Again, radius of Blue circle = (21 + 10.5)cm = 31.5 cm

∴ Area of Blue ring

= \(\frac{22}{7}\left(31.5^2-21^2\right)\)

= \(\frac{22}{7} \times(992.25-441)\)

= \(\frac{22}{7} \times 551.25\)

= 1732.5 cm2

Again, the radius of the Black Circle

= (31.5 + 10.5)cm

= 42cm

∴ Area of Black circle

= \(\frac{22}{7} \times\left(42^2-31.5^2\right)\)

= \(\frac{22}{7} \times(1764-992.25)\)

= \(\frac{22}{7} \times 771.75=2425.5 \mathrm{~cm}^2\)

Again, radius of white circle = (42 + 10.5) cm

∴ Area of White circle

= \(=\frac{22}{7} \times\left(52.5^2-42^2\right)\)

= \(\frac{22}{7} \times(2756.25-1764)\)

= \(\frac{22}{7} \times 992.25=3118.5 \mathrm{~cm}^2\)

Area Related To Circles Archery Target

Question 4. The wheels of a car are of diameter 80 cm each. How many complete revolutions does each wheel make in 10 minutes when the car is travelling at a speed of 66 km per hour?

Solution:

The diameter of the wheel of a car, 2r= 80 cm

⇒ r = 40 cm

∴ Distance covered in one revolution

= circumference

= \(2 \pi r=2 \times \frac{22}{7} \times 40=\frac{1760}{7} \mathrm{~cm}\)

Now, speed of car = 66 km/hr

= \(\frac{66 \times 1000 \times 100}{60} \mathrm{~cm} / \mathrm{min}\)

∴ Distance covered in 10 minutes

= \(\frac{66 \times 1000 \times 100}{60} \times 10 \mathrm{~cm}\)

= 11 x 1000 x 100 cm

Now, the number of revolutions made by the wheel

= \(\frac{\text { Total distance covered }}{\text { Distance covered by wheel in 1 revolution }}\)

= \(\frac{11 \times 1000 \times 100}{1760 / 7}\)

= \(=\frac{11 \times 1000 \times 100 \times 7}{1760}=4375 \text { Ans }\)

Question 5. Tick the correct answer in the following and justify your choice: if the perimeter and the area of a circle are numerically equal, then the radius of the circle is:

  1. 2 units
  2. units
  3. 4 units
  4. 7 units

Solution:

1. 2 units

Let r be the radius of the circle.

Given that, in numerical form, area of circle = perimeter of circle

⇒ πr2 = 2πr ⇒ r = 2 units

NCERT Exemplar Class 10 Maths Area Related to Circles with solutions

NCERT Exemplar Solutions for Class 10 Maths Chapter 12  Area Related To Circles Exercise 12.2

Question 1. Find the area of a sector of a circle with a radius of 6 cm if the angle of the sector is 60°.

Solution:

Here, the radius of the circle, r = 6 cm

The angle of the sector, θ= 60°

∴ Area of sector = \(\frac{\theta}{360^{\circ}} \times \pi r^2\)

= \(\frac{60^{\circ}}{360^{\circ}} \times \frac{22}{7} \times 6 \times 6 \mathrm{~cm}^2\)

= \(\frac{132}{7} \mathrm{~cm}^2 \text { or } 18.86 \mathrm{~cm}^2\)

The area of a sector of a circle is 18.86 c

Question 2. Find the area of a quadrant of a circle whose circumference is 22 cm.

Solution:

Circumference of the circle, 2πr = 22

⇒ \(2 \times \frac{22}{7} \times r=22 \quad \Rightarrow \quad r=\frac{7}{2} \mathrm{~cm}\)

Now, the area of the quadrant of a circle

⇒ \(\frac{1}{4} \pi r^2=\frac{1}{4} \times \frac{22}{7} \times \frac{7}{2} \times \frac{7}{2}\)

∴ \(\frac{77}{8} \mathrm{~cm}^2\)

The area of a quadrant of a circle = \(\frac{77}{8} \mathrm{~cm}^2\)

Question 3. The length of the minute hand of a clock is 14 cm. Find the area swept by the minute hand in 5 minutes.

Solution:

Length of minute hand of clock = 14 cm

∴ The radius of the circle, r = 14 cm

∵ The angle subtended by minute hand in 60 min = 360°

∴ Angle subtended by minute hand in 1 minute = \(\frac{360^{\circ}}{60^{\circ}}=6^{\circ}\)

∴ The angle subtended by minute hand in 5 minutes = 30°

∴ From the formula,

area of sector of circle = \(\frac{\theta \pi r^2}{360^{\circ}}\)

= \(30^{\circ} \times \frac{22 \times(14)^2}{7 \times 360^{\circ}}\)

= \(\frac{22 \times 14 \times 2}{12}\)

= \(\frac{616}{12}=\frac{154}{3} \mathrm{~cm}^2\)

The area swept by the minute hand in 5 minutes =\(\frac{154}{3} \mathrm{~cm}^2\)

Question 4. A chord of a circle of radius 10 cm subtends a right angle at the centre. Find the area of the corresponding:

  1. Minor segment
  2. Major sector

Solution:

Given, the radius of the circle, AO = 10 cm.

The perpendicular is drawn from the centre of the circle to the chord of the circle which bisects this chord.

Area Related To Circles Radius Of The Circle

AD = DC

And ∠AOD = ∠COD

= 45°

∴ ∠AOC = ∠AOD + ∠COD

= 45° + 45° = 90°

In the right ΔAOD,

⇒ \(\sin 45^{\circ}=\frac{A D}{A O} \quad \Rightarrow \quad \frac{1}{\sqrt{2}}=\frac{A D}{10}\)

AD = 5√2 cm

and \(\cos 45^{\circ}=\frac{O D}{A O} \Rightarrow \frac{1}{\sqrt{2}}=\frac{O D}{10}\)

⇒ OD = 5√2 cm

Now, AC = 2AD

2 x 5√2 = 10√2 cm

Now, the area of ΔAOC

= \(\frac{1}{2} A C \times O D\)

= \(\frac{1}{2} \times 10 \sqrt{2} \times 5 \sqrt{2}=50 \mathrm{~cm}^2\)

Now the area of the sector

= \(\frac{\theta \pi r^2}{360^{\circ}}=\frac{90^{\circ}}{360^{\circ}} \times 3.14 \times(10)^2\)

= \(\frac{314}{4}=78.5 \mathrm{~cm}^2\)

1. Area of minor segment AEC

= area of sector OAEC – area of AOC

= 78.5 – 50 = 28.5 cm2

2. Area of major sector OAFGCO

= area of circle- area of sector OAEC

= πr2– 78.5 = 3.14 x (10)2 – 78.5

314 – 78.5 = 235.5cm2

Question 5. In a circle of radius 21 cm, an arc subtends an angle of 60° at the centre. Find:

  1. The length of the arc
  2. The area of the sector formed by the arc
  3. The area of the segment is formed by the corresponding chord.

Solution:

Here, the radius of circle r = 21 cm

The angle subtended by are at the centre, θ = 60°

1. Length of arc

= \(l=\frac{\theta}{360^{\circ}} \times 2 \pi r\)

= \(\frac{60^{\circ}}{360^{\circ}} \times 2 \times \frac{22}{7} \times 21=22 \mathrm{~cm}\)

2. Area of sector formed by the arc

= \(\frac{\theta}{360^{\circ}} \times \pi r^2\)

= \(\frac{60^{\circ}}{360^{\circ}} \times \frac{22}{7} \times 21 \times 21\)

= 231 cm2

3. Area of segment formed by the corresponding chord

= \(\frac{\pi r^2 \theta}{360^{\circ}}-\frac{1}{2} r^2 \sin \theta\)

= \(231-\frac{1}{2} \times 21 \times 21 \times \sin 60^{\circ}\)

= \(\left(231-\frac{441 \sqrt{3}}{4}\right) \mathrm{cm}^2\)

Question 6. A chord of a circle of radius 15 cm subtends an angle of 60° at the centre. Find the areas of the corresponding minor and major segments of the circle.

(Use π = 3.14 and √3 = 1.73)

Solution:

Given

A chord of a circle of radius 15 cm subtends an angle of 60° at the centre.

Here, the radius of the circle, r = 15 cm

The angle subtended by a chord at the centre, θ = 60°

∴ Area of the corresponding minor segment

= \(\frac{\pi r^2 \theta}{360^{\circ}}-\frac{1}{2} r^2 \sin \theta\)

= \(r^2\left(\frac{\pi \theta}{360^{\circ}}-\frac{1}{2} \sin \theta\right)\)

= \(15 \times 15\left(\frac{3.14 \times 60^{\circ}}{360^{\circ}}-\frac{1}{2} \sin 60^{\circ}\right)\)

= \(225\left(\frac{3.14}{6}-\frac{1}{2} \times \frac{\sqrt{3}}{2}\right)\)

= \(225\left(\frac{3.14}{6}-\frac{1.73}{4}\right)=20.4375 \mathrm{~cm}^2\)

Now, the area of the circle = πr2

= 3.14 x 15 x 15 = 706.5 cm2

∴ Area of major segment = area of circle – an area of the minor segment

= (706.5 – 20.4375) cm2

= 686.0625 cm2.

The areas of the corresponding minor and major segments of the circle = 686.0625 cm2.

Question 7. A chord of a circle of radius 12 cm subtends an angle of 120° at the centre. Find the area of the corresponding segment of the circle.
(Use π = 3.14 and √3 = 1.73)

Solution:

Given

A chord of a circle of radius 12 cm subtends an angle of 120° at the centre.

Here, the radius of the circle, r = 12 cm

The angle subtended by the chord at the centre, θ = 120°

Area of the corresponding minor segment

= \(\frac{\pi r^2 \theta}{360^{\circ}}-\frac{1}{2} r^2 \sin \theta\)

= \(r^2\left(\frac{\pi \theta}{360^{\circ}}-\frac{1}{2} \sin \theta\right)\)

= \(12 \times 12 \times\left(\frac{3.14 \times 120^{\circ}}{360^{\circ}}-\frac{1}{2} \times \sin 120^{\circ}\right)\)

= \(144\left(\frac{3.14}{3}-\frac{1}{2} \times \frac{\sqrt{3}}{2}\right)\)

= \(144\left(\frac{3.14}{3}-\frac{1.73}{4}\right)\)

= 88. 44 cm2

The area of the corresponding segment of the circle = 88. 44 cm2

Question 8. A horse is tied to a peg at one corner of a square-shaped grass field of side 15 m by means of a 5 m long rope. Find:

  1. The area of that part of the field in which the horse can graze.
  2. The increase in the grazing area, if the rope were 10 m long instead of 5m. (Use π = 3.14)

Area Related To Circles A Horse Is Tied To A Peg

Solution:

Given

A horse is tied to a peg at one corner of a square-shaped grass field of side 15 m by means of a 5 m long rope.

Side of square field = 15 m

The radius of the circle, r = 5m

The angle formed by chord, θ = 90°

1. Area of that part of the field where the horse can graze the grass

= \(\frac{\theta}{360^{\circ}} \times \pi r^2=\frac{90^{\circ}}{360^{\circ}} \times 3.14 \times 5^2\)

= 19.625 m2

Area of that part of the field where the horse can graze the grass = 19.625 m2

2. If the length of the rope is 10 m then the increase in the area of grazing.

= \(\frac{90^{\circ}}{360^{\circ}} \times 3.14 \times\left(10^2-5^2\right)\)

= \(\frac{1}{4} \times 3.14 \times 75\)

= 58.875 m2.

If the length of the rope is 10 m then the increase in the area of grazing = 58.875 m2.

Area Related to Circles problems and solutions Class 10

Question 9. A brooch is made with silver wire in the form of a circle with a diameter of 35 mm. The wire is also used in making 5 diameters which divide the circle into 10 equal sectors as shown. Find:

  1. The total length of the silver wire required.
  2. The area of each sector of the brooch.

Area Related To Circles A Brooch Is Made With Silver Wire In The Form Of A Circle

Solution:

Given

A brooch is made with silver wire in the form of a circle with a diameter of 35 mm. The wire is also used in making 5 diameters which divide the circle into 10 equal sectors as shown.

1. Diameter of circular brooch,

2r = 35 mm

= \(r=\frac{35}{2} \mathrm{~mm}\)

Length of required silver wire = 2πr

= \(2 \times \frac{22}{7} \times \frac{35}{2} \mathrm{~mm}=110 \mathrm{~mm}\)

Now, the length of 5 diameters = 5 x 2r

= \(5 \times 2 \times \frac{35}{2}=175 \mathrm{~mm}\)

Length of total wire = (110 + 175) mm

= 285 mm

The total length of the silver wire required = 285 mm

2. For each sector,

angle, \(\theta=\frac{360^{\circ}}{10^{\circ}}=36^{\circ}\)

∴ Area = \(\frac{\theta}{360^{\circ}} \times \pi r^2\)

= \(\frac{36^{\circ}}{360^{\circ}} \times \frac{22}{7} \times \frac{35}{2} \times \frac{35}{2}\)

= \(\frac{385}{4} \mathrm{~cm}^2\)

The area of each sector of the brooch = \(\frac{385}{4} \mathrm{~cm}^2\)

Question 10. An umbrella has 8 ribs which are equally spaced. Assuming an umbrella to be a flat circle of radius 45 cm, find the area between the two consecutive ribs of the umbrella.

Area Related To Circles Umbrella To Be A Flat Circle

Solution:

Given

An umbrella has 8 ribs which are equally spaced. Assuming an umbrella to be a flat circle of radius 45 cm

The radius of the umbrella,

r = length of ribs of umbrella = 45 cm

Here, number of sectors = 8

∴ Angle of sector = \(\theta=\frac{360^{\circ}}{8}=45^{\circ}\)

Now, the area between two ribs = area of the sector

= \(\frac{\theta}{360^{\circ}} \times \pi r^2\)

= \(\frac{45^{\circ}}{360^{\circ}} \times \frac{22}{7} \times 45 \times 45 \mathrm{~cm}^2\)

= \(\frac{22275}{28} \mathrm{~cm}^2\)

The area between the two consecutive ribs of the umbrella = \(\frac{22275}{28} \mathrm{~cm}^2\)

Question 11. A car has two wipers which do not overlap. Each wiper has a blade of length 25 cm sweeping through an angle of 115°. Find the total area cleaned at each sweep of the blades.

Solution:

Given, the length of the wiper blade

r = 25 cm = r(say)

The angle formed by this blade, θ =115°

∴ Area cleaned by a blade = area of sector formed by blade

= \(\frac{\theta \pi r^2}{360^{\circ}}=115^{\circ} \times \frac{22}{7 \times 360^{\circ}} \times(25)^2\)

= \(\frac{23 \times 22}{7 \times 72} \times 625=\frac{23 \times 11 \times 625}{7 \times 36}\)

= \(\frac{158125}{252} \mathrm{~cm}^2\)

∴ Total area cleaned by two blades

= 2 x area cleaned by a blade

= \(\frac{2 \times 158125}{252}=\frac{158125}{126} \mathrm{~cm}^2\)

The total area cleaned at each sweep of the blades =\(\frac{158125}{126} \mathrm{~cm}^2\)

Question 12. To warn ships of underwater rocks, a lighthouse spreads a red-coloured light over a sector of angle 80° to a distance of 16.51cm. Find the area of the sea over which the ships are warned. (Use π = 3.14)

Solution:

Given, the angle of the sector, θ = 80°

And distance or radius, r = 16.5 km

Area of sector

= \(\frac{\theta \pi r^2}{360^{\circ}}=\frac{80^{\circ} \times 3.14 \times(16.5)^2}{360^{\circ}}\)

= \(\frac{2 \times 3.14 \times 272.25}{9}=\frac{1709.73}{9}=189.97 \mathrm{~km}^2\) which is the area of the sea over which the ships are warned.

Question 13. A round table cover has six equal designs as shown. If the radius of the cover is 28 cm, find the cost of making the designs at the rate of ₹ 0.35 per cm2. (Use √3 = 1.7)

Area Related To Circles A Round Table Cover Has Six Equal Designs

Solution:

Given

A round table cover has six equal designs as shown. If the radius of the cover is 28 cm

The radius of the table cover, r = 28 cm

Number of designs formed on table cover = 6

∴ The angle formed by each chord at the centre

= \(\frac{360^{\circ}}{6}=60^{\circ}\)

Now, the area of segment

= \(\frac{\pi r^2 \theta}{360^{\circ}}-\frac{1}{2} r^2 \sin \theta\)

= \(r^2\left(\frac{\pi}{360^{\circ}}-\frac{1}{2} \sin \theta\right)\)

⇒ Area of 6 segments

= \(6 r^2\left(\frac{\pi}{360^{\circ}}-\frac{1}{2} \sin \theta\right)\)

= \(6 \times 28 \times 28\left(\frac{60^{\circ}}{360^{\circ}} \times \frac{22}{7}-\frac{1}{2}-\sin 60^{\circ}\right)\)

= \(6 \times 28 \times 28\left(\frac{11}{21}-\frac{1}{2} \times \frac{\sqrt{3}}{2}\right)\)

= \(=6 \times 28 \times 28\left(\frac{11}{21}-\frac{1.73}{4}\right)=464.8 \mathrm{~cm}^2\)

Now, the total cost of making the design

= ₹ 0.35 x 464.8 = ₹ 162.68

The total cost of making the design = ₹ 162.68

Question 14. The area of a sector of angle p (in degrees) of a circle with radius R is

  1. \(\frac{p}{180} \times 2 \pi R\)
  2. \(\frac{p}{180} \times \pi R^2\)
  3. \(\frac{p}{360} \times 2 \pi R\)
  4. \(\frac{p}{720} \times 2 \pi R^2\)

Solution:

4. \(\frac{p}{720} \times 2 \pi R^2\)

Area of sector = \(\frac{\theta}{360^{\circ}} \times \pi r^2\)

= \(\frac{p}{360^{\circ}} \times \pi R^2=\frac{p}{720} \times 2 \pi R^2\)

NCERT Exemplar Solutions for Class 10 Maths Chapter 12  Area Related To Circles Exercise 12.3

Question 1. Find the area of the shaded region in the figure, if PQ= 24 cm, PR = 7 cm and O is the centre of the circle.

Area Related To Circles The Area Of The Shaded Region

Solution:

Here, PQ = 24 cm and PR = 7 cm

∵ The angle in a semicircle is a right angle.

∴ ∠QPR = 90°

In ΔPQR,

QR2 = PQ2 + PR2 = 242 + 72 = 625

QR = 25 cm

If r is the radius of the circle, then

2r = 25 cm

= \(r=\frac{25}{2} \mathrm{~cm}\)

Area of shaded region = area of semicircle – area of ΔPQR

= \(\frac{1}{2} \pi r^2-\frac{1}{2} \times P Q \times P R\)

= \(\frac{1}{2} \times \frac{22}{7} \times \frac{25}{2} \times \frac{25}{2}-\frac{1}{2} \times 24 \times 7\)

= \(\frac{6875}{28}-84=\frac{4523}{28} \mathrm{~cm}^2\)

The area of the shaded region =\(\frac{4523}{28} \mathrm{~cm}^2\)

Question 2. Find the area of the shaded region, if the radii of the two concentric circles with centre O are 7 cm and 14 cm respectively and ∠AOC = 40°.

Area Related To Circles Radii Of The Two Concentric Circles With Centre

Solution:

Given

The radii of the two concentric circles with centre O are 7 cm and 14 cm respectively and ∠AOC = 40°.

Here, OA = 14 cm and OB = 7 cm

The angle of the sector, θ = 40°

∴ Area of the shaded portion

= \(\frac{\theta}{360^{\circ}} \times \pi \times\left(O B-O A^2\right)\)

= \(\frac{40^{\circ}}{360^{\circ}} \times \frac{22}{7} \times\left(14^2-7^2\right)\)

= \(\frac{1}{9} \times \frac{22}{7} \times 147=51.33 \mathrm{~cm}^2\)

The area of the shaded region =51.33 cm².

Question 3. Find the area of the shaded region, if ABCD is a square of side 14 cm and APD and BPC are semicircles.

Area Related To Circles Areas Of Two Semicircles

Solution:

Given

ABCD is a square of side 14 cm and APD and BPC are semicircles.

Side of square = 14

Area of square = 14 x 14 cm2 = 196 cm2

Diameter of each semicircle 2r = side of square = 14 cm

⇒ r = 7 cm

Area of one semicircle = \(\frac{1}{2} \pi r^2\)

Area of two semicircles = \(2 \times \frac{1}{2} \pi r^2=\pi r^2\)

= \(\frac{22}{7} \times 7 \times 7=154 \mathrm{~cm}^2\)

Area of shaded portion = area of the square – the sum of areas of two semicircles

= (196 – 154) cm2 = 42 cm2

The area of the shaded region = 42 cm2

Question 4. Find the area of the shaded region given, where a circular arc of radius 6 cm has been drawn with vertex O of an equilateral triangle OAB of side 12 cm as the centre.

Area Related To Circles Each Side Of Equilateral Triangle

Solution:

Given

A circular arc of radius 6 cm has been drawn with vertex O of an equilateral triangle OAB of side 12 cm as the centre.

Each side of the equilateral triangle = 12 cm

and each angle = 60°

Now, the area of an equilateral triangle

= \(\frac{\sqrt{3}}{4} \times(\text { side })^2=\frac{\sqrt{3}}{4} \times 12 \times 12 \mathrm{~cm}^2\)

= 36√3 cm2

The radius of the circle, r = 6 cm

Angle of major sector, 0 = 360° – 60° = 300°

∴ Area of major sector

= \(\frac{\theta}{360^{\circ}} \times \pi r^2\)

= \(\frac{300^{\circ}}{360^{\circ}} \times \frac{22}{7} \times 6 \times 6=\frac{660}{7} \mathrm{~cm}^2\)

Now, the area of the shaded region = area of the equilateral triangle + area of a major sector.

= \(\left(36 \sqrt{3}+\frac{660}{7}\right) \mathrm{cm}^2\)

The area of the shaded region = \(\left(36 \sqrt{3}+\frac{660}{7}\right) \mathrm{cm}^2\)

Question 5. From each A corner of a square of side 4 cm a quadrant of a circle of radius 1 cm is cut and also a circle of diameter 2 cm is cut as shown. Find the area of the remaining portion of the square.

Area Related To Circles A Square

Solution:

Given

From each A corner of a square of side 4 cm a quadrant of a circle of radius 1 cm is cut and also a circle of diameter 2 cm is cut as shown.

Side of square = 4 cm

∴ Area of square = (side)2 = 42 = 16 cm2

The radius of a quadrant of a circle, r = 1 cm

∴ Area of four quadrants

= \(4 \times \frac{1}{4} \pi r^2\)

= \(\frac{22}{7} \times 1 \times 1=\frac{22}{7} \mathrm{~cm}^2\)

For the circle inside the square diameter, 2R = 2 cm ⇒ R = 1 cm

Area of this circle = \(\pi R^2=\frac{22}{7} \times 1 \times 1=\frac{22}{7} \mathrm{~cm}^2\)

Now, area of shaded portion = \(16-\left(\frac{22}{7}+\frac{22}{7}\right)=\frac{68}{7} \mathrm{~cm}^2\).

Question 6. In a circular table covered of radius 32 cm, a design is formed leaving an equilateral triangle ABC in the middle as shown. Find the area of the design.

Area Related To Circles An Equilateral Triangle

Solution:

Given

In a circular table covered of radius 32 cm, a design is formed leaving an equilateral triangle ABC in the middle as shown.

ΔABC is an equilateral triangle.

Area Related To Circles An Equilateral Triangle..

∴ ∠A = ∠B = ∠C = 60°

AD is perpendicular to BC.

∴ OA, OB, and OC are the radii of the circle.

Given that,

OA = OB = OC = 32 cm

∠BOC = 2

∠BAC = 2 x 60° = 120°

∴ \(\angle B O D=\frac{1}{2} \times 120^{\circ}=60^{\circ}\)

In ΔBOD

⇒ \(\sin 60^{\circ}=\frac{B D}{O B} ⇒ \frac{\sqrt{3}}{2}=\frac{B D}{32}\)

BD = 16√3 cm

BC = 2 BD = 32√3 cm

Area of ΔABC = \(\frac{\sqrt{3}}{4} \times B C^2\)

= \(\frac{\sqrt{3}}{4} \times(32 \sqrt{3})^2=768 \sqrt{3} \mathrm{~cm}^2\)

Area of circle = π(OB)2

= \(\frac{22}{7} \times 32 \times 32=\frac{22528}{7} \mathrm{~cm}^2\)

Now, the area of the shaded portion

= area of a circle – an area of ΔABC

= \(\left(\frac{22528}{7}-768 \sqrt{3}\right) \mathrm{cm}^2\).

The area of the shaded portion = \(\left(\frac{22528}{7}-768 \sqrt{3}\right) \mathrm{cm}^2\).

Important questions for Class 10 Maths Chapter 12 with solutions

Question 7. In the ABCD is a square of side 14 cm. With centres A. B. C and D, four circles are drawn such that each circle touch externally two of the remaining three circles. Find the area of the shaded region.

Area Related To Circles Areas Of Four Quadrants

Solution:

Side of square ABCD = 14 cm

∴ Area of square = (14)2 =196 cm2

Radius of first quadrant \(r=\frac{14}{2}=7 \mathrm{~cm}\)

∴ The sum of area’s four quadrants

= \(4 \times \frac{1}{4} \pi r^2=\pi r^2\)

= \(\frac{22}{7} \times 7 \times 7=154 \mathrm{~cm}^2\)

Now, the area of the shaded portion = area of the square – the sum of areas of four quadrants

= 196 = 154 = 42 cm2

The area of the shaded region = 42 cm2

Question 8. depicts a racing track whose left and right ends are semicircular. The distance between the two inner parallel line segments is 60 m and they are each 106 m long. If the track is 10 m wide, find:

  1. The distance around the track along its inner edge.
  2. The area of the track.

Area Related To Circles Depicts A Racking Track Left And Right Ends Are Semicircular

Solution:

Hence OB O’C = \(\frac{60}{2}=30 \mathrm{~m}\)

Area Related To Circles Depicts A Racking Track Left And Right Ends Are Semicircular.

AB = CD = 10m

∴ OA = O’D = (30 + 10) m = 40 m

1. Distance covered in one round along the inner edges of the path.

= BC + EH + 2 x circumference of semicircle

= \(106+106+2 \times \frac{1}{2} \times 2 \pi \times 30\)

= \(212+2 \times \frac{22}{7} \times 30=\frac{2804}{7} \mathrm{~m}\)

2. Inner radius r = OB = 30 m

Outer radius R = OA = 40 m

Area of path = 2 x area of ABCD + 2 x area of semicircular rings

= \(=2 \times 106 \times 10+\frac{1}{2} \times \pi\left(R^2-r^2\right)\)

= \(2120+\frac{22}{7} \times\left(40^2-30^2\right)\)

= 2120 + 2200 = 4320 m2

Area of path is 4320 m2

Question 9. In the figure, AB and CD are two diameters of a circle (with centre O) perpendicular to each other and OD is the diameter of the smaller circle. If OA = 7 cm, find the area of the shaded region.

Area Related To Circles Diameters Of A Circle

Solution:

Given

In the figure, AB and CD are two diameters of a circle (with centre O) perpendicular to each other and OD is the diameter of the smaller circle. If OA = 7 cm

The diameter of the smaller circle

OD = OA = 7 cm

∴ Radius r = \(\frac{7}{2}=3.5 \mathrm{~cm}\)

∴ Area of smaller circle = nr2

= \(\frac{22}{7} \times 3.5 \times 3.5 \mathrm{~cm}^2=38.5 \mathrm{~cm}^2\)

Area of semicircle OAQCPBO

= \(\frac{1}{2} \pi(O A)^2\)

= \(\frac{1}{2} \times \frac{22}{7} \times 7 \times 7=77 \mathrm{~cm}^2\)

Area of ΔABC = = \(\frac{1}{2} \times A B \times O C\)

= \(\frac{1}{2} \times 14 \times 7=49 \mathrm{~cm}^2\)

Now the area of the shaded portion = area of the smaller circle + area of OAQCPBO – an area of ABC

= 38.5 + 77 –  49 = 66. cm2

The area of the shaded region = 66. cm2

Question 10. The area of an equilateral triangle 11 ABC is 17320.5 cm2. With each vertex of the triangle as the centre, a circle is drawn with a radius equal to half the length of the side of the triangle. Find the area of the shaded region. (Use π= 3.24 and √3 = 1.73205).

Area Related To Circles Area Of An Equilateral Triangle

Solution:

Given

The area of an equilateral triangle 11 ABC is 17320.5 cm2. With each vertex of the triangle as the centre, a circle is drawn with a radius equal to half the length of the side of the triangle.

Let the radius of each circle = r

Side of equilateral triangle = r + r = 2r

Now, area of equilateral triangle = \(\)

Given that, √3r2 = 17320.5 ⇒ 1.73205r2 = 17320.5

⇒ r2 = 10000 ⇒ r = 100 cm

Each angle of an equilateral triangle, θ = 60° Now, the area of sectors of three circles

= \(3 \times \frac{\theta}{360^{\circ}} \times \pi r^2\)

= \(3 \times \frac{60^8}{360^{\circ}} \times 3.14 \times(100)^2\)

= 15700 cm2

Area of shaded region = area of equilateral ABD = area of three sectors

= (17320.5 – 15700) cm2

= 1620.5 cm2

The area of the shaded region = 1620.5 cm2.

Question 11. On a square handkerchief, nine circular designs each of a radius of 7 cm are made. Find the area of the remaining portion of the handkerchief.

Area Related To Circles A Square Handkerchief Nine Circular Designs

Solution:

Given, the radius of each circle, r = 7 cm

Diameter of circle, d = 14 cm = 42 cm (∵ diameter = 2 x radius)

Three horizontal circles touch each other.

Length of square = 3 x 14 cm = 42 cm

Now area of a circle = πr2 = (7)2

= \(\frac{22}{7} \times(7)^2=154 \mathrm{~cm}^2\)

∴ Area of 9 circles = 9 x 154 = 1386 cm2

Now, area of square ABCD = (side)2

= (42)2 = 1764 cm2

∴ Area of the remaining part of the handkerchief

= 1764 – 1386 = 378 cm2

The area of the remaining portion of the handkerchief = 378 cm2

Question 12. The OACB is a quadrant of a circle with centre O and a radius of 3.5 cm. If OD = 2 cm. find the area of the

  1. Quadrant OACB
  2. Shaded region.

Area Related To Circles A Quadrant Of A Circle

Solution:

Given

The OACB is a quadrant of a circle with centre O and a radius of 3.5 cm. If OD = 2 cm

Radius of quadrant AOB. r= 3.5 cm

1. Area of quadrant OACB

= \(\frac{1}{4} \pi^2\)

= \(\frac{1}{4} \times \frac{22}{7} \times 3.5 \times 3.5=\frac{77}{8} \mathrm{~cm}^2\)

2. Area of ΔOBD

= \(\frac{1}{2} \times O B \times O D\)

= \(\frac{1}{2} \times 3.5 \times 2=3.5 \mathrm{~cm}^2=\frac{7}{2} \mathrm{~cm}^2\)

Area of the shaded portion

= area of quadrant OACB – area of OBD

= \(\left(\frac{77}{8}-\frac{7}{2}\right) \mathrm{cm}^2=\frac{49}{8} \mathrm{~cm}^2\)

Area of the shaded portion =\(\frac{49}{8} \mathrm{~cm}^2\)

Question 13. In the square O.ABC is inscribed in a quadrant OPBQ. If OA = 20 cm, find the area of the shaded region. (Use π = 3.14)

Area Related To Circles Each Side Of A Square

Solution:

Given

In the square O.ABC is inscribed in a quadrant OPBQ. If OA = 20 cm

Each side of square OABC = 20 cm

∴ Area of OABC = (20)2 = 400 cm2

Area of OABC = (20)2 = 400 cm2

In ΔOAB,

OB2 = OA2 ~ AB2 = 202 + 202 = 800

⇒ OB = 20√2cm

which is the radius of quadrant OPBQ.

Area of quadrant OPBQ

= \(\frac{1}{4} \pi(O B)^2=\frac{1}{4} \times 3.14 \times(20 \sqrt{2})^2\)

= 628 cm2

Now, the area of the shaded portion

= area of quadrant OPBD – area of square OABC

= (628 – 400) cm2 = 228 cm2

The area of the shaded region = 228 cm2

Question 14. AB and CD are respectively arcs of two concentric circles of radii 21 cm and 7 cm and centre O . If ∠AOB = 30°, find the area of the shaded region.

Area Related To Circles Arcs Of Two Concentric Circles

Solution:

Given

AB and CD are respectively arcs of two concentric circles of radii 21 cm and 7 cm and centre O . If ∠AOB = 30°

Here Q = 30°

Area of the shaded portion

= Area of sector OAB – area of sector OCD

= \(\frac{\theta}{360^{\circ}} \times \pi(O B)^2-\frac{\theta}{360^{\circ}} \times \pi(O C)^2\)

= \(\frac{\theta}{360^{\circ}} \times \pi\left[(O B)^2-(O C)^2\right]\)

= \(\frac{30^{\circ}}{360^{\circ}} \times \frac{22}{7} \times\left(21^2-7^2\right)\)

= \(\frac{1}{12} \times \frac{22}{7} \times 392 \mathrm{~cm}^2=\frac{308}{3} \mathrm{~cm}^2\)

Area of the shaded portion \(\frac{308}{3} \mathrm{~cm}^2\)

CBSE Class 10 Maths Area Related to Circles exemplar question answers

Question 15. The ABC is a quadrant of a circle of radius 14 cm and a semicircle is drawn with BC as diameter. Find the area of the shaded region.

Area Related To Circles Quadrant Of A Circle

Solution:

Given

The ABC is a quadrant of a circle of radius 14 cm and a semicircle is drawn with BC as diameter.

For the quadrant ABC,

Radius r = 1 4 cm

∴ Area of quadrant ABC

= \(\frac{1}{4} \pi r^2\)

= \(\frac{1}{4} \times \frac{22}{7} \times 14 \times 14=154 \mathrm{~cm}^2\)

Area of \(\triangle A B C=\frac{1}{2} \times A B \times A C\)

= \(\frac{1}{2} \times 14 \times 14=98 \mathrm{~cm}^2\)

In right ABC,

BC2 = AC2 + AB2 = 142 + 142 = 392

BC = 14√2 cm

∴ For the semicircle formed on BC

Radius \(R=\frac{B C}{2}=\frac{14 \sqrt{2}}{2}=7 \sqrt{2} \mathrm{~cm}\)

and area of semicircle

= \(\frac{1}{2} \pi R^2\)

= \(\frac{1}{2} \times \frac{22}{7} \times(7 \sqrt{2})^2=154 \mathrm{~cm}^2\)

Now, the area of the shaded portion

= area of ΔABC + area of semicircle – area of quadrant ABC

= (98 + 154 – 154) cm2 = 98 cm2

The area of the shaded region = 98 cm2

Question 16. Calculate the area of the designed region in the figure common between the two quadrants of circles of radius 8 cm each.

Area Related To Circles Common Between The Two Quadrants Of Circles

Solution:

The radius of each of quadrants ABMD and BNDC, r = 8 cm

Area Related To Circles Radius Of Each Quadrants

∴ Area of two quadrants

= \(2 \times \frac{1}{4} \pi r^2\)

= \(2 \times \frac{1}{4} \times \frac{22}{7} \times 8 \times 8\)

= \(\frac{704}{7} \mathrm{~cm}^2\)

and area of square ABCD = AB2 = 82 = 64 cm2

Now, the area of the shaded portion

= area of two quadrants – area of square ABCD

= \(\left(\frac{704}{7}-64\right) \mathrm{cm}^2\)

= \(\frac{256}{7} \mathrm{~cm}^2\)

The area of the designed region = \(\frac{256}{7} \mathrm{~cm}^2\)

NCERT Exemplar Solutions for Class 10 Maths Chapter 12  Area Related To Circles Multiple Choice Questions And Answers

Question 1. If the sum of the circumference of two circles of radii R1 and R2is equal to the circumference of a circle of radius R, then:

  1. R1 + R2 = R
  2. R1 + R2 > R
  3. R1 + R2 < R
  4. None of these

Answer: 1. R1 + R2 = R

Question 2. If the sum of the areas of two circles of radii and R1 and R2 is equal to the area of a circle of radius R, then:

  1. R1 + R2 = R
  2. R1 + R2 < R
  3. R12 + R22 = R2
  4. R12 + R22 < R2

Answer: 3. R12 + R22 = R2

Question 3. If the area of a circle is 154 cm2, then its circumference is:

  1. 11 cm
  2. 22 cm
  3. 44 cm
  4. 66 cm

Answer: 3. 44 cm

Question 4. The area of the largest triangle inscribed in a semicircle of radius r is:

  1. r2
  2. \(\frac{1}{2} r^2\)
  3. 2r2
  4. r2√2

Answer: 1. r2

Question 5. The area of the largest square inscribed in a circle of radius 8 cm is:

  1. 256 cm2
  2. 64 cm2
  3. 128 cm2
  4. 32 cm2

Answer: 3. 128 cm2

NCERT Class 10 Area of Circle and Sector problems

Question 6. The area largest circle inscribed in a square of side 4 cm is:

  1. 16π cm2
  2. 8π cm2
  3. 6π cm2
  4. 4π cm2

Answer: 2. 8ir cm2

Question 7. If the circumference of a circle and the perimeter of a square are equal, then the ratio of their areas is:

  1. 22:7
  2. 14:11
  3. 7:22
  4. 11:14

Answer: 2. 14:11

Question 8. In the adjoining figure, the perimeter of sector OAB is:

Area Related To Circles The Perimeter Of A Sector

  1. \(\frac{64}{3} \mathrm{~cm}\)
  2. 26 cm
  3. \(\frac{64}{5} \mathrm{~cm}\)
  4. 19 cm

Answer: 1. \(\frac{64}{3} \mathrm{~cm}\)

Question 9. The length of the minute hand of a clock is 14 cm. The area swept by hand in one minute will be:

  1. 10.26 cm2
  2. 10.50 cm2
  3. 10.75 cm2
  4. 11.0 cm2

Answer: 1. 10.26 cm2

NCERT Exemplar For Class 10 Maths Chapter 11 Constructions

NCERT Exemplar For Class 10 Maths Chapter 11 Constructions Division Of A Line Segment

To divide a line segment (internally) in a given ratio m: n

Working Rule: (Internal division)

Draw a line segment AB of a given length.

Draw a ray AX making an acute angle XAB with AB.

Mark (m + n) points A1, A2, A3, …, Am+n on AX such that AA1 = A1A2 = A2A3 = … = Am+n-1 Am+n.

Join Am+n B.

Through Am, draw AmY || Am+n B (if m: n) meeting AB at Y. So, Y divides AB internally in the ratio m: n.

Read and Learn More Class 10 Maths Solutions Exemplar

Constructions Meeting AB At Y

NCERT Exemplar Class 10 Maths Chapter 11 Constructions

Through An, draw An1Z || Am+n B (if n: m) meeting AB at Z. So, Z divides AB internally in the ratio n: m.

Constructions Meeting AB At Z

In Short:

Sum (m +n) endpoint

first (m) Parallel (Y)  (say)

NCERT Exemplar For Class 10 Maths Chapter 11 Constructions

NCERT Exemplar For Class 10 Maths Chapter 11 Constructions Solved Problems

Question 1. Determine a point which divides a line segment 7 cm long, internally in the ratio 2:3.

Solution:

Steps of Construction:

  1. Draw a line segment AB = 7 cm by using a ruler.
  2. Draw any ray malting an acute ZBAC with AB.
  3. Along AC, mark off (2 + 3) = 5 points A1, A2, A3, A4 and A5 such that AA1 = A1A2 = A2A3 = A3A4 = A4A5.
  4. Join BA5
  5. Through A2 draw a line A2P parallel to A5B by making an angle equal to \(\angle A A_5 B\) at A2 intersecting AB at A point P.

The point P so obtained is the required point.

Constructions Meeting Acute Angle

Justification: In ΔA5B,

A2P || A5B (Construction)

∴ \(\frac{A A_2}{A_2 A_5}=\frac{A P}{P B}\) (by B.P theorem)

⇒ \(\frac{2}{3}=\frac{A P}{P B}\) (Construction)

⇒ AP : PB = 2: 3

i.e., P divides AB internally in the ratio 2 : 3.

Alternate Method:

Draw the line segment AB = 7 cm.

Draw any ray AC making an acute angle ∠BAC with AB.

Draw a ray BD parallel to Ac by making ∠ABC equal to angle ∠BAC.

Mark off 2 points A1 and A2 on AC and 3 points B1, B2, B3 on AD such that AA1 = A1A2 = BB1 = B1B2 = B2B3

Join B3A2, suppose it intersects AB at point P. Then, P is the required point.

Constructions Meeting Intersects AB At Point P

To Divide a Line Segment (Externally) in a Given Ratio m: n

Working Rule: (External Division)

Constructions Meeting To Divided A Line Segment

Question 2. Determine a point which divides a line segment 6 cm long externally in the ratio 5 : 3.

Solution:

Steps of Construction:

  1. Draw a line segment AB = 6 cm.
  2. Draw any ray making an acute ∠BAX with AB.
  3. Along AX, mark off (larger among the ratios) 5 points A1, A2, A3, A4, A5 such that AA1 = A1A2 = A2A3 = A3A4 = A4A5.
  4. Join the point A2 (5-3) with end point B.
  5. Draw a line parallel to A2B from A5 (larger among the ratios) which meets AB produced at P.

The point P, so obtained is the required point such that AP: BP = 5 : 3.

Constructions Meets AB Produced At P

Justification: In AA5P,

Since A2B || A5P, (Construction)

∴ \(\frac{A P}{B P}=\frac{A A_5}{A_2 A_5}\) (by B.P theorem)

⇒ \(\frac{A P}{B P}=\frac{5}{3}\) (Construction)

Question 3. Determine a point which divides a line segment 6 cm long externally in the ratio 3:5.

Solution:

Steps of Construction:

  1. Draw a line segment AB = 6 cm.
  2. Draw any ray making an acute ∠ABX with AB.
  3. Along BX, mark off (larger among the ratios) 5 points B1, B2, B3, B4 and B5 such that BB1 =B1B2 = B2B3 — B3B4 = B4B5.
  4. Join the point B2 (5 – 3) with endpoint A
  5. Draw a line parallel to B2A from B5 (larger among the ratios) which meets BA produced at P.

The point P so obtained is the required point such that AP: BP = 3:5.

Constructions Meets BA Produced At P

Justification: In ΔPBB5,

Since, B2A || B5P (Construction)

∴ \(\frac{B_2 B_5}{B B_5}=\frac{A P}{B P}\) (by B.P theorem)

⇒ \(\frac{3}{5}=\frac{A P}{B P}\) (Construction)

i.e., P divides AB externally in the ratio of 3:5

Class 10 Maths Constructions Exemplar Solutions

NCERT Exemplar For Class 10 Maths Chapter 11 Constructions To Construct A Triangle Similar To A Given Triangle

Question 1. Construct a triangle similar to a given triangle ABC such that each of its sides is \(\frac{2}{3} \mathrm{rd}\) of the corresponding sides of the triangle ABC. It is given that AB = 4 cm, BC = 5 cm and AC = 6 cm.

Solution:

Given

It is given that AB = 4 cm, BC = 5 cm and AC = 6 cm.

Steps of construction:

  1. Take BC = 5cm and Construct ΔABC with BA = 4cm and CA = 6cm.
  2. Divide BC into three equal parts.
  3. Let C be a point on BC such that \(B C^{\prime}=\frac{2}{3} B C\)
  4. Draw A’C parallel to AC through C” intersecting BA at A’. ΔA’BC” is the required triangle.

Constructions Triangle

Question 2. Construct an isosceles triangle whose base is 6 cm and altitude 4 cm. Then construct another triangle whose sides are \(\frac{3}{4}\) times the corresponding sides of the first triangle.

Solution:

Steps to Construction:

  1. Draw a line segment BC = 6 cm.
  2. Draw a perpendicular bisector of BC.
  3. From mid-point D of BC on perpendicular bisector mark DA = 4 cm, join AB and AC.
  4. Below BC make an acute angle ∠CBZ.
  5. Along BZ mark off four points B1, B2, B3 and B4 such that BB1 = B1B2 = B2B3 = B3B4.
  6. Join B4C.
  7. From B3 draw B3E parallel to B4C meeting BC at E.
  8. From E draw EF || CA meeting BA at F. Then, ΔFBE is the required triangle.

Constructions Isosceles Triangle

Question 3. Construct a quadrilateral ABCD with AB = 3 cm, AD = 2.7 cm, DB = 3.6 cm, ∠B =110° and BC = 4.2 cm. Construct another quadrilateral A’BC’D’ similar to quadrilateral ABCD so that diagonal BD’ = 4.8 cm.

Solutions:

Steps to construction:

  1. Draw a line segment BC = 4.2 cm
  2. At B, construct angle YBC = 110°
  3. With centre B and a radius equal to 3 cm, draw an arc-cutting BT at A.
  4. With centre A and a radius equal to 2.7 cm, draw an arc.
  5. With centre B and radius equal to 3.6 cm, draw another arc cutting the previous arc at D.
  6. Join AD, CD and BD. Then, ABCD is the required quadrilateral.
  7. Produce BD to D’ such that BD’ = 4.8 cm.
  8. From D’, draw a line parallel to DA which cuts BY at A’.
  9. From D’, draw a line parallel to DC which cuts BC produced at D’.

Then, □ - Wiktionary, the free dictionaryA’BC’D’ is the required quadrilateral similar to □ - Wiktionary, the free dictionaryABCD.

Constructions A Quadrilateral

Question 4. Construct a cyclic quadrilateral ABCD in which AB = 4.2 cm, BC = 5.5 cm, CA = 4.6 cm and AD = 3 cm. Also, construct a quadrilateral similar to □ - Wiktionary, the free dictionaryABCD whose sides are 1 .5 times the corresponding sides of □ - Wiktionary, the free dictionaryABCD.

Solution:

Steps to construction:

  1. Draw a line segment AB = 4.2 cm.
  2. With centre A and a radius equal to 4.6 cm, draw an arc.
  3. With centre B and radius equal to 5.5 cm, draw another arc cutting the previous arc at C.
  4. Join AC and BC.
  5. Draw the perpendicular bisectors of any two sides say AB and BC respectively of ΔABC. Let them intersect each other at O.
  6. Taking O as the centre and radius as OA or OB or OC, draw a circle. This is the circumcircle of ΔABC.
  7. With centre A and radius equal to 3 cm, cut an arc on the opposite side of B, to cut the circle at D.
  8. Join AD and CD. Then, □ - Wiktionary, the free dictionaryABCD is the required cyclic quadrilateral.
  9. Produce Ac to C’ such that \(A C^{\prime}=1.5 \times A C \text { i.e., }\left(1+\frac{1}{2}\right) A C \Rightarrow A C+\frac{1}{2} \times 4.6\) i.e., 2.3cm more.
  10. From C’, draw a line parallel to CD which meets AD produced at D’.
  11. From C’, draw a line parallel to CB which meets AB produced at B’. Then, □ - Wiktionary, the free dictionaryAB’C’D’ is the required quadrilateral similar to cyclic quadrilateral ABCD.

Constructions A Cyclic Quadrilateral

NCERT Exemplar For Class 10 Maths Chapter 11 Constructions Of Tangents To A Circle

Question 1. Take a point O on the plane of the paper. With O as the centre draw a circle of radius 4 cm. Take a point on this circle and draw a tangent at P.

Solution:

Steps of Construction:

  1. Take a point O on the plane of the paper and draw a circle of a given radius of 4 cm.
  2. Take a point P on the circle and join OP.
  3. Construct ∠OPT = 90°.
  4. Produce TP to T’ to obtain the required tangent TPT’.

Constructions Tangent At P

Question 2. Draw a circle of radius 3 cm. Take a point P on it. Without using the centre of the circle, draw a tangent to the circle at point P.

Solution:

Steps of construction:

  1. Draw any chord PQ through the given point P on the circle.
  2. Take a point R on the circle and join P and Q to a point R.
  3. Construct ∠QPY = ∠PRQ and on the opposite side of the chord PQ.
  4. Produce YP to X to get YPX as the required tangent.

Constructions Tangent To The Circle At Point P

Question 3. Draw a circle of radius 2.5 cm. Take a point at a distance of 5 cm from the centre of the circle. From point P, draw two tangents to the circle.

Solution:

Steps of Construction:

  1. Take a point O in the plane of the paper and draw a circle of radius 2.5 cm.
  2. Mark a point P at a distance of 5.0 cm from the centre O and, join OP.
  3. Draw the right bisector of OP, intersecting OP at Q.
  4. Taking Q as a centre and OQ = PQ as the radius, draw a circle to intersect the given circle at T and T.
  5. Join PT and PT’ to get the required tangents.

Constructions Two Tangent To The Circle

Question 4. Draw a pair of tangents to a circle of radius 5 cm inclined to each other at an angle of 60°.

Solution:

Steps of Construction:

  1. Take a point O on the plane of the paper and draw a circle with centre O and radius OA = 5 cm.
  2. At O construct radii OA and OB such that ∠AOB equals 120° i.e., supplement of the angle between the tangents.
  3. Draw perpendiculars to OA and OB at A and B respectively suppose these perpendiculars intersect at P. Then, PA and PB are required tangents.

Constructions Pair Of Tangent To The Circle

Question 5. Draw a circle of radius 4 cm. Take a point P outside the circle. Without using the centre of the circle, draw two tangents to the circle from point P.

Solution:

Steps of Construction:

  1. Draw a line segment of 4 cm.
  2. Take a point P outside the circle and draw a second PAB, intersecting the circle at A and B.
  3. Produce AP to C such that AP = CP.
  4. Draw a semi-circle with CB as the diameter.
  5. Draw PD ⊥ CB, intersecting the semi-circle at D.
  6. Widi P as centre and PD as radius draw arcs to intersect the given circle at T and T’.
  7. Join PT and PT’. Then, PT and PT’ are the required tangents.

Constructions Two Tangent Two The Circle From Point P

NCERT Exemplar Solutions for Constructions Class 10

NCERT Exemplar For Class 10 Maths Chapter 11 Constructions Exercise 11.1

Question 1. Draw a line segment of length 7.6 cm and divide it in the ratio 5:8. Measure the two parts.

Solution:

Steps of construction :

  1. Draw a line segment AB = 7.6 cm.
  2. Draw a ray AX which forms an acute angle from AB.
  3. Cut (8 + 5) = 13 equal marks on ray AX and mark them X1, X2, X3, X4, …, X13.
  4. Join X13 to B.
  5. Draw X5C || X13 B from X5 which meets AB at C.

So, point C divides the line segment AB in the ratio 5:8.

On measuring two line segments, we get AC = 4.7 cm, BC = 2.9 cm

Constructions Line Segment

Verification: In ΔABX13 and ΔACX5, CX5 || BX13

∴ \(\frac{A C}{C B}=\frac{A X_5}{X_5 X_{13}}=\frac{5}{8}\)

⇒ AC: AB = 5:8

Question 2. Construct a triangle of sides 4 cm, 5 cm and 6 cm and then a triangle similar to it whose sides are \(\frac{2}{3}\) of the corresponding sides of the first triangle.

Solution:

Steps of construction:

  1. Construct a ΔABC such that BC = 6 cm, AC = 5 cm and AB = 4 cm.
  2. Draw a ray BX such that ∠CBX is at an acute angle.
  3. Mark three points X1, X2 and X3 on BX such that BX1 = X1X2 = X2X3.
  4. Join X3 and C.
  5. Draw a line parallel to line X3C from X2 which intersects BC at C’.
  6. Draw a line parallel to line CA from C which meets BA at A’.

So, ΔA’B C’ is the required triangle.

Constructions Two Triangles

Verification: By construction

X3C || X2C’  ⇒ \(\frac{B X_2}{X_2 X_3}=\frac{B C^{\prime}}{C^{\prime} C}\)

but \(\frac{B X_2}{X_2 X_3}=\frac{1}{2} \quad ⇒ \quad \frac{B C^{\prime}}{C^{\prime} C}=\frac{2}{1}\)

⇒ \(\frac{C^{\prime} C}{B C^{\prime}}=\frac{1}{2}\)

Adding 1 on both sides,

⇒ \(\frac{C^{\prime} C}{B C^{\prime}}+1=\frac{1}{2}+1\)

⇒ \(\frac{C^{\prime} C+B C^{\prime}}{B C^{\prime}}=\frac{1+2}{2} = \frac{B C}{B C^{\prime}}=\frac{3}{2}\)

Now, in ΔBC’A’ and ΔBCA,

CA || C’A’

from A.A. similarity, ΔBC’A’ ∼ ΔBCA

⇒ \(\frac{A^{\prime} B}{A B}=\frac{A^{\prime} C^{\prime}}{A C}=\frac{B C^{\prime}}{B C} \quad\left[\text { each }=\frac{2}{3}\right]\)

Question 3. Construct a triangle with sides 5 cm, 6 cm and 7 cm and then another triangle whose sides are \(\frac{7}{5}\) of the corresponding sides of the first triangle.

Solution:

Steps of construction:

  1. Draw a line segment BC = 5 cm
  2. Draw two arcs with centres B and C of radii 7 cm and 6 cm respectively which intersect each other at A.
  3. Join BA and CA. ΔABC is the required triangle.
  4. Draw a ray BX from B downwards, making an acute angle ∠CBX.
  5. Mark seven points B1, B2, B3, B4, B5, B6 and B7 on B8 such that BB1 = B1B2 = B2B3 = B3B4 = B4B5 = B5B6 = B6B7
  6. Join B5C and draw B7M || B5C from B7, which intersects the produced BC at M.
  7. Draw MN || CA from point M which intersects the produced BA at N.

Now ΔNBM is the required triangle whose sides are \(\frac{7}{5}\) of the sides of ΔABC.

Constructions A Triangle And Then Another Triangle

Justification:

By construction,

B7M || B5C

∴ \(\frac{B C}{C M}=\frac{5}{2}\)

Now, \(\frac{B M}{B C}=\frac{B C+C M}{B C}\)

= \(1+\frac{C M}{B C}=1+\frac{2}{5}=\frac{7}{5}\)

∴ \(\frac{B M}{B C}=\frac{7}{5}\)

and, MN || CA

∴ ΔABC ∼ ΔNBM

and \(\frac{N B}{A B}=\frac{B M}{B C}=\frac{M N}{C A}=\frac{7}{5}\)

Question 4. Construct an isosceles triangle whose base is 8 cm and altitude 4 cm and then another triangle whose sides are \(1 \frac{1}{2}\) times the corresponding sides of the isosceles triangle.

Solution:

Steps of construction:

  1. Draw the line segment BC = 8cm.
  2. Draw the perpendicular bisector OQ of BC which intersects BC at P.
  3. Take PA = 4 cm along PO.
  4. Join BA and CA. Now ΔABC is the required isosceles triangle.
  5. Draw a ray BX from B making acute angle ∠CBX.
  6. Mark three points B1, B2 and B3 on BX such that BB1 = B1B2 = B2B3
  7. Join B2C and draw B3N || B2C from B3 which intersects the Produced BC at N.
  8. Draw NM || CA from point N which intersects the produced BA at M.

Then ΔMBN is the required rectangle.

Constructions An Isosceles triangle

Justification:

∵ B3 || B2C (by construction)

∴ \(\frac{B C}{C N}=\frac{2}{1}\)

Now \(\frac{B N}{B C}=\frac{B C+C N}{B C}=1+\frac{C N}{B C}=1+\frac{1}{2}=1 \frac{1}{2}\)

Question 5. Draw a triangle ABC with side BC = 6 cm, AB = 5 cm and ABC = 60°. Then construct a triangle whose sides are \(\frac{4}{3}\) of the corresponding sides of the triangle ABC.

Solution:

Steps of construction:

  1. Construct a triangle ABC such that BC = 6 cm, AB = 5 cm and ∠ABC = 60°.
  2. Draw a ray \(\overrightarrow{B X}\) such that CBX is an acute angle.
  3. Mark four points X1, X2, X3, and X4 on BX such that BX1 = X1X2 = X2X3 = X3X4.
  4. Join X4C.
  5. Draw X3C’ || X4C which intersects BC at C.
  6. Draw a line from C, parallel to CA which intersects BC at A’.

So, ΔA’BC’ is the required triangle.

Constructions Triangle ABC

Verification: By construction

X4C || X3C’ [from B.P.T.]

∴ \(\frac{B X_3}{B X_4}=\frac{B C^{\prime}}{B C} \text { but } \frac{B X_3}{B X_4}=\frac{3}{4}\) (by construction)

⇒ \(\frac{B C^{\prime}}{B C}=\frac{3}{4}\) → (1)

Now, CA || C’A’ (by construction)

ΔBC’A’ BCA [from A.A. similarity]

⇒ \(\frac{A^{\prime} B}{A B}=\frac{A^{\prime} C^{\prime}}{A C}=\frac{B C^{\prime}}{B C}=\frac{3}{4}\) [from (1)].

Chapter 11 Constructions Class 10 Maths Exemplar

Question 6. Draw a triangle ABC with side BC = 7 cm, ∠B = 45°, ∠A = 105°. Then, construct a triangle whose sides are \(\frac{4}{3}\) times the corresponding sides of ΔABC.

Solution:

Steps of construction:

  1. Construct a ΔABC such that BC = 7 cm, ∠B = 45° and ∠A = 105°.
  2. Draw a ray BX such that ∠CBX is at an acute angle.
  3. Mark four points X1, X2, X3 and X4 on BX such that:
    Bx1 = X1X2 = X2X3 = X3X4.
  4. Draw a line from X4 parallel to X3C which intersects BC produced at C’.
  5. Draw a line from C parallel to CA, that intersects BA produced at A’.
  6. Thus, ΔA’BC’ is the required triangle.

Constructions A Triangle Corresponding Sides Of ABC

Verification: By construction,

C’A’ || CA [from A.A. similarity]

ΔABC ∼ ΔA’BC’

⇒ \(\frac{A^{\prime} B}{A B}=\frac{A^{\prime} C^{\prime}}{A C}=\frac{B C^{\prime}}{B C}\) → (1)

Again, by construction

X4C’ || X3C

∴ BX4C’ BX3C

⇒ \(\frac{B C^{\prime}}{B C}=\frac{B X_4}{B X_3}\)

but \(\frac{B X_4}{B X_3}=\frac{4}{3} \Rightarrow \frac{B C^{\prime}}{B C}=\frac{4}{3}\) → (2)

from (1) and (2),

∴ \(\frac{A^{\prime} B}{A B}=\frac{A^{\prime} C^{\prime}}{A C}=\frac{B C^{\prime}}{B C}=\frac{4}{3}\).

Question 7. Draw a right triangle in which the sides (other than hypotenuse) are of lengths 4 cm and 3 cm. Then construct another triangle whose sides are \(\frac{5}{3}\) times the corresponding sides of the given triangle.

Solution:

Steps of construction:

  1. Draw a line segment BC = 4 cm.
  2. Draw a line segment AB = 3 cm from B which makes a 90° angle from BC.]
  3. Join AC. ΔABC is the given right-angled triangle.
  4. Draw an acute angle ∠CBY from B downwards.
  5. Mark 5 points B1, B2, B3, B4 and B5 on BY such that BB1 = B1B2 = B2B3 = B3B4 = B4B5.
  6. Join B3C.
  7. Draw B5C’ || B3 C from B5, which meets the produced BC at C.
  8. Draw C’A’ || CA from C’ which meets the produced BA at A’

So, ΔA’BC’ is the required triangle.

Constructions A Right Triangle

Justification:

By construction, B5C’ || B3C

∴ \(\frac{B C}{C C^{\prime}}=\frac{3}{2}\)

Now, \(\frac{B C^{\prime}}{B C}=\frac{B C+C C^{\prime}}{B C}=1+\frac{C C^{\prime}}{B C}\)

= \(1+\frac{2}{3}=\frac{5}{3}\)

and, C’A’ = CA

∴ ΔABC ∼ ΔA’BC’

and \(\frac{A^{\prime} B}{A B}=\frac{B C^{\prime}}{B C}=\frac{A^{\prime} C^{\prime}}{C A}=\frac{5}{3}\)

NCERT Exemplar For Class 10 Maths Chapter 11 Constructions Exercise 11.2

Question 1. Question 1. Draw a circle of radius 6 cm. From a point 10 cm away from its centre, construct the pair of tangents to the circle and measure their lengths.

Solution:

Steps of construction:

  1. Mark a point O.
  2. Draw a circle with centre O and a radius of 6 cm.
  3. Mark a point P at a distance of 10 cm from the centre.
  4. Join O and P
  5. Bisects OP at point M.
  6. With the centre at point M, draw a circle with a radius MO or MP which intersects the given circle at A and B.
  7. Join PA and PB. So, PA and PB are two required tangents. On measuring PA = PB = 9.6 cm.

Constructions The Pair Of Tangent To The Circle

Verification: Join OA and OB. Since OP is a diameter.

∠OAP = 90º; ∠OBP = 90º [angle in semicircle]

Again OA and OB are the radii of a circle.

⇒ PA and PB are tangents to the circle.

Class 10 Constructions Questions with Solutions

Question 2. Construct a tangent to a circle of radius 4 cm from a point on the concentric circle of radius 6 cm and measure its length. Also, verify the measurement by actual calculation.

Solution:

Steps of construction:

  1. Draw two circles of radii 4 cm and 6 cm with a centre O.
  2. Mark a point P on a larger circle.
  3. Join O and P.
  4. Find the point M of the perpendicular bisector of.OP.
  5. With centre M and radius OM or PM draw a circle which intersects the smaller circle at A and B.
  6. Join A and P.

So, PA is the required tangent. On measuring PA = 4.5 cm.

Constructions A Tangent To A Circle Of Radius

Verification: Join O and A.

∠PAO = 90° [angle in semcircle]

PA ⊥ OA

∵ OA is the radius of the small circle.

∴ PA is a tangent of the smaller circle

Question 3. Draw a circle of radius 3 cm. Take two points P and Q on one of its extended diameters each at a distance of 7 cm from its centre. Draw tangents to the circle from these two points P and Q.

Solution:

Given : P and Q are two points on a diameter of the circle of radius 3 cm.

and OP = OQ = 7cm

We have to construct the tangents to the circle from P and Q.

Steps of construction:

  1. Draw a circle of radius 3 cm with centre O.
  2. Produce its diameter on both sides and take two points P and Q on it such that OP = OQ = 7 cm.
  3. Bisect OP and OQ. Let E and F be the mid-points of OP and OQ respectively.
  4. Draw a circle with centre E and radius OE, which intersects the given circle (0, 3) at M and N. Again draw a circle with centre F and radius OF which intersects the given circle at P’ and Q’.
  5. Join PM, PN, QP’ and QQ’. These are the required tangents from P and Q to the circle (0, 3).

Constructions Tangents To The Circle Of Two Points

Justification:

Join OM and ON. ∠OMP lies in the semicircle, so ∠OMP = 90°. OM is the radius of the circle, so MP is the tangent to the circle. Similarly PN, QP’ and OQ’ are also the tangents to the circle.

Question 4. Draw a pair of tangents to a circle of radius 5 cm inclined to each other at an angle of 60°.

Solution:

Steps of construction:

  1. Construct a circle with centre O and radius = 5 cm.
  2. Draw ∠AOB = 120°.
  3. Draw a perpendicular on OA from point A.
  4. Draw a perpendicular on OB from B.
  5. Both perpendiculars intersect each other at point C.

So, CA and CB are the required tangents to the circle, inclined at a 60° angle.

Constructions A Pair Of Tangents To A Circle

Verification:

In quadrilateral OACB, from angle sum property.

⇒ 120° + 90° + 90° + ∠ACB = 360°

⇒ 300° + ∠ACB = 360°

⇒ ∠ACB = 360°- 300° = 60°

Question 5. Draw a line segment AB of length S cm. Taking A as the centre, draw a circle of radius 4 cm and taking B as the centre, draw another circle of radius 3 cm. Construct tangents to each circle from the centre of the other circle.

Solution:

Steps of construction:

  1. Draw a line segment AB = 8 cm.
  2. Draw a circle of radius 4 cm taking A as the centre.
  3. Draw another circle of radius 3 cm talcing B as the centre.
  4. Draw the perpendicular bisector of AB and find the mid-point M of AB.
  5. Draw the circle with centre M and radius MA or MB which intersects the circle with centre A at P and Q and the circle with centre F at R and S.
  6. Join BP and FQ. So, BP and FQ are the required tangents on a circle with centre A from B.
  7. Now join RA and SA.

So, RA and SA are the tangents on a circle with centre B from A.

Constructions Tangents To Each Circle From The Centre Of The Other Circle

Verification: Join A and P.

∠APB = 90° => BP ⊥ AP

but AP is the radius of a circle with centre A.

⇒ AP is a tangent of the circle with centre A.

Similarly, BQ is also a tangent of the circle with centre A. Similarly AR and AS are the tangents of the circle with centre B.

NCERT Exemplar problems and solutions for Class 10 Constructions

Question 6. Let ABC be a right triangle in which AB = 6 cm, BC = 8 cm and B = 90° BD is the perpendicular from b on AC. The circle through B, C, and D is drawn. Construct the tangents from A to this circle.

Solution:

Given

Let ABC be a right triangle in which AB = 6 cm, BC = 8 cm and B = 90° BD is the perpendicular from b on AC. The circle through B, C, and D is drawn.

Steps of construction:

  1. Draw line segments AB = 6 cm and BC= 8 cm perpendicular to each other. Join AC. Now ΔABC is a right-angled triangle.
  2. Taking the mid-point F of BC as the centre and radius of 4 cm, draw a circle which passes through points B, C and D.
  3. Join AF and bisects A it. Let O be the midpoint of AF.
  4. The circle drawn with f centre O and radius OA intersects the given circle at B and M.
  5. Join AB and AM, which are the required tangents.

Constructions Right Triangle

Justification:

Join FM and FB. Now ∠AMF lies in a semicircle,

so ∠AMF = 90° ⇒ FM ⊥ AM

∵ FM is the radius of the circle, so AM is the tangent to the circle and F is the centre.

Similarly, AB is also the tangent to the circle with centre F.

Class 10 Maths Chapter 11 Constructions solved questions

Question 7. Draw a circle with the help of a bangle Take a point outside the circle. Construct the pair of tangents from this point to the circle.

Solution:

Steps of construction:

  1. Draw a circle using a bangle.
  2. Draw two chords AP and MT. The perpendicular bisectors of AP and MT intersect each other at O, which is the centre of the circle.
  3. Take a point R outside the circle. Join OR and bisect it.
  4. Let Q be the mid-point of OR. The circle drawn with centre Q and radius OQ intersects the given circle at S and N.
  5. Join RS and RN, so RS and RN are the required tangents from R.

Constructions The Pair Of Tangents From This Point To The Circle

Justification:

Join OS and ON. ∠OSR lies in a semicircle, so

∠OSR = 90° ⇒ OS || SR

∵ OS is the radius of a circle with a centre of O, so SR is the centre of that circle whose centre is O. Similarly, RN is also the tangent to the circle with a centre of O.

Interior Of The Cranial Vault

Interior Of The Cranial Vault Definition

It is the internal surface of the skull cap.

Interior Of The Cranial Vault Shape

This is ovoid like norma verticalis.

Interior Of The Cranial Vault Bones

Same bones contribute to this part which were observed in norma verticalis, i.e.

  1. Frontal bone, anteriorly.
  2. Occipital bone, posteriorly
  3. Parietal bones, on each side.

Interior Of The Cranial Vault Sutures

Sutures correspond with those observed in norma verticalis which are as follows:

  1. Coronal suture, between frontal and parietal bones.
  2. Sagittal suture, between two parietal bones.
  3. Lambdoid suture, between parietal and occipital bones.

Interior Of The Cranial Vault Features

  • Frontal Crest
    • It is a midline crest seen at its anterior part.
    • Falx cerebri is attached to it.
  • Sagittal Sulcus
    • It is an anteroposterior groove in the median plane.
    • It is narrow anteriorly but widens posteriorly.
    • It contains superior sagittal sinus.
    • Falx cerebri is attached to its margins.
  • Bregma And Lambda
    • These mark the junctions of sagittal suture with coronal and lambdoid sutures respectively (see norma verticalis).
  • Parietal Foramen
    • It pierces the parietal bone on each side of midline about 3.5 cm in front of lambda. Emissary vein passes through it.
  • Granular Foveolae
    • These are irregular depressions on each side of sagittal sulcus.
    • These are produced by arachnoid granulations.
    • These are deep and more abundant in aged skull.
  • Grooves For Meningeal Vessels
    • Grooves for anterior (frontal) twigs of middle meningeal vessels are located just behind the coronal suture.
    • Grooves for parietal twigs of middle meningeal vessels are more posteriorly placed. These run backwards and upwards.
  • Impressions For Cerebral Gyri
    • These are less marked in cranial vault in contrast to the interior of the base of skull where cerebral impressions are well defined.

Interior Of The Cranial Vault Skull Cap Internal Surface

Ribs: Anatomy, Ligaments And Clinical Notes

Ribs General Considerations

  1. Ribs are bilateral bony arches forming the greater part of the thoracic wall.
  2. Normally there are 12 pairs of ribs which are numbered from above downwards.
  3. The length of the ribs increases from the 1st to the 7th rib and then decreases from the 7th to the 12th rib. Therefore, the 7th rib is the longest rib.
  4. The ribs are arranged obliquely, i.e. the anterior end is at a lower level than the posterior end. The obliquity is maximum in the 9th rib.
  5. The 8th rib is the most laterally projected rib.
  6. The width of the rib gradually reduces from above downwards.
  7. Intercostal spaces (gaps between adjacent ribs) are deeper in front than behind and deeper in the upper part than the lower part.

Ribs The Thoracic Cage Anterior And Posterior Views

First Ribs

Distinguishing Features

  1. It is the shortest.
  2. It is the broadest.
  3. It is most curved.
  4. It has no twisting.
  5. Angle coincides with tubercle.
  6. Head has got only a single facet.
  7. The costal groove is absent.
  8. The neck is rounded and elongated.
  9. It is flattened from above downwards and therefore has inner and outer borders and superior and inferior surfaces.

Side Determination

  1. Keep the larger end anteriorly and the smaller end posteriorly.
  2. Keep the surface of the shaft having two grooves separated by a ridge, superiorly.
  3. Keep the concave border towards the inner side and the convex border towards the outer side.

Note: Keep the rib on a flat surface considering its position in your own body.

The rib belongs to the side on which both ends touch the surface simultaneously. If the rib is placed on the wrong side then only the anterior end will be touching the table top.

Anatomical Position

  1. The posterior end is nearer the midline than the anterior end.
  2. The posterior end is 3.5 cm higher than the anterior end.
  3. The upper surface faces upwards as well as forwards.

Features And Attachments

Just like a typical rib, the first rib is comprised of two ends (anterior and posterior) and a shaft.

  1. Anterior End
    1. It is the larger end.
    2. It meets with 1st costal cartilage.
  2. Posterior End
    • It consists of the head, neck, and tubercle.
      1. Head
        1. It is small and rounded.
        2. It has a single rounded facet for articulation with the body of 1st thoracic vertebra to form a costovertebral joint.
        3. The capsular ligament of 1st costovertebral joint is attached to the margins of the facet.
        4. The radiate ligament is attached to the anterior margin of the head.
      2. Neck
        1. It is rounded.
        2. It is directed upwards, backward, and laterally.
        3. The inferior costotransverse ligament is attached to its posterior surface.
        4. The following structures form the anterior relations of the neck from medial to lateral:
          1. Sympathetic chain.
          2. First posterior intercostal vein.
          3. Superior intercostal artery.
          4. First thoracic root (T) of brachial plexus.
          5. Note: Remember SVAN for the relations of the anterior aspect of the neck from medial to lateral in which the S-sympathetic chain, V-Vein,- Artery, and N-Nerve.
      3. Tubercle
        1. It is large and prominent.
        2. It articulates with the transverse process of 1st thoracic vertebra.
        3. The lateral costotransverse ligament is attached laterally to the tubercle.
  3. Shaft
    • It consists of two borders (outer and inner) and two surfaces (upper and lower).
      1. Outer border
        1. It is convex.
        2. It is thick posteriorly and thin anteriorly.
        3. 1st digitation of the serratus anterior arises from its middle.
        4. It is related to the scalenus posterior muscle in its posterior part while clavipectoral fascia and pectoralis major muscle in its anterior part.
      2. Inner border
        1. It is concave.
        2. The scalene tubercle is situated near its middle.
        3. Sibson’s fascia (suprapleural membrane) is attached to it.
      3. Upper surface
        1. It is rough and irregular.
        2. It presents two shallow grooves separated by a ridge.
        3. The ridge continues medially with the scalene tubercle along the inner border.
        4. The scalenus anterior is inserted on the ridge and scalene tubercle.
        5. The subclavian vein lies in the groove anterior to the ridge.
        6. The subclavian artery along with the lower trunk of the brachial plexus occupies the posterior groove.
        7. Note: Remember ‘VAN’ is the sequence of structures occupying the grooves on the superior surface from anterior to posterior, i.e. Vein, Artery, and Nerve.
        8. The area anterior to the groove for the subclavian vein provides attachments to the subclavius muscle (anteriorly) and costoclavicular ligament (posteriorly). These attachments are located near the anterior end because they also extend over the costal cartilage.
        9. Scalenus medius is inserted on the rough area posterior to the groove for the subclavian artery.
      4. Lower surface
        1. It is smooth.
        2. It is related to costal pleura.
        3. Intercostal muscles are attached to this surface near its outer border.
        4. 1st intercostal nerve and vessels are related to this surface mainly in its posterior part.

Ribs First Rib Of Left Side Superior Aspect

Ribs First Rib Of Left Side Superior View

Ribs First Rib Of Left Side Inferior Aspect

Sternum: Anatomy, Parts, Pain And Diagram Notes

Sternum

Sternum Terminology

‘Sternum’ is derived from the Greek word ‘sternum’ which means chest. Sternum is also called ‘breast bone’.

It has three parts; manubrium, body, and xiphoid process. The manubrium is a Latin word that means ‘handle’. The term ‘xiphoid’ is borrowed from the Greek word ‘xiphos’ which means ‘sword’.

Sternum Location

It is a flat bone whose long axis is vertical. It lies in the median part of the anterior thoracic wall. Its surfaces are anterior and posterior. Its anterior surface also faces a little upwards.

Sternum Location Of Sternum

Sternum Length

It is about 7 inches (17 cm) long.

Sternum Structure

It is made up of mainly spongy bone and thus it is rich in red bone marrow.

Sternum Features

Sternum is made up of three pieces from above downwards:

  1. Manubrium.
  2. Body.
  3. Xiphoid process.

Sternum Manubrium

It is somewhat triangular in shape and is wider above than below. It has two surfaces (anterior and posterior) and four borders (superior, inferior, and two lateral).

Sternum Sternum Anterior Aspect

Sternum The Body

It has two surfaces (anterior and posterior), two borders (right lateral

Sternum Side Views Of Sternum And Thoracic Vertebrae

Sternum Xiphoid Process

It is the lowest and smallest part of the sternum and is of variable shape. It has two surfaces (anterior and posterior), two borders (right lateral and left lateral), and two ends (upper and lower).

Sternum Sternum Posterior Aspect

Sphenoid Bone: Anatomy, Function And Development Notes

Sphenoid Bone

Sphenoid Bone Terminology

‘Sphenoid’ is derived from the Greek word ‘sphen’ which means ‘a wedge’. The bone is so named because it is wedged between the frontal bone in front and the occipital bone behind.

Sphenoid Bone Anatomical Position

  1. Hypophyseal fossa faces upwards.
  2. Pterygoid processes descend vertically downwards.
  3. Openings of sphenoidal sinuses are directed forward.

Sphenoid Bone Articulations

The Sphenoid is a key bone in the cranial skeleton as it articulates with the following eight bones:

  1. Frontal
  2. Parietal
  3. Temporal
  4. Occipital
  5. Vomer
  6. Zygomatic
  7. Palatine
  8. Ethmoid

Sphenoid Bone Shape

Sphenoid resembles a ‘bat’ with its wings stretched out.

Sphenoid Bone Features And Attachments

Sphenoid consists of a central body, four wings (two greater and two lesser), and two pterygoid processes (right and left).

Sphenoid Bone Body

It has six surfaces (superior, inferior, anterior, posterior, and two lateral) and a pair of air-filled cavities (sphenoidal sinuses).

1. Surfaces

  1. Superior (cerebral) surface: It shows of following features from anterior to posterior.
    1. Jugum Sphenoidale
      1. It is smooth.
      2. It articulates with the posterior margin of the cribriform plate.
      3. It is related on each side to the gyrus rectus of the cerebral hemisphere and olfactor tract.
    2. Sulcus Chiasmatis
      1. It is a transverse groove behind the jugum sphenoidale
      2. Optic chiasma lies just above it.
      3. It leads laterally into the optic canal.
    3. Tuberculum Sellae
      • It is an elevation just behind the sulcus chiasmatis.
    4. Sella Turcica
      1. It is a depressed area behind the tuberculum sellae.
      2. The hypophyseal fossa is the deepest part of the Sella turcica. It lodges the pituitary gland.
      3. The anterior part of Sella turcica is bounded on each side by an elevation called the middle clinoid process.
    5. Dorsum Sellae
      1. It is a square plate of bone behind the sella turcica.
    6. Posterior Clinoid Process
      1. Superior angles of dorsum sellae project laterally into posterior clinoid processes.
      2. Attached margin of tentorium cerebelli is attached to this process on each side.
    7. The upper part of the clivus
      1. It is sloping behind the dorsum sellae.
      2. It is formed by the posterior parts of the body and dorsum sellae.
      3. It supports the pons.
  2. Posterior Surface 
    • It is rough.
    • It articulates with the basilar part of the occipital bone.
  3. Anterior And Inferior Surfaces 
    1. The midline of the anterior surface is marked by a triangular crest called a sphenoidal crest.
    2. The sphenoidal crest articulates with the upper part of the posterior border of the perpendicular plate of the ethmoid.
    3. The midline of the inferior surface is marked by a triangular spine called a sphenoidal rostrum. It fits into the groove between the alae of the vomer.
    4. Both anterior and inferior surfaces of the body on either side of the midline, are occupied by a thin plate of bone called sphenoidal concha.
    5. Each sphenoidal concha consists of an anterior part which is vertical and quadrangular and a posterior part which is horizontal and triangular.
      1. Anterior Part
        1. It consists of an upper and lateral depressed area which completes the posterior ethmoidal sinus and articulates below with the orbital process of palatine bone.
        2. Its lower and medial part forms part of the roof of the nasal cavity and is perforated above by the round opening through which the sphenoidal sinus communicates with the sphenoethmoidal recess of the nasal cavity.
      2. Posterior Part
        • It forms part of the roof of the nasal cavity and completes the sphenopalatine foramen.
  4. Lateral Surface
    1. Its lower part unites with the greater wing and medial pterygoid plate.
    2. Its upper part is marked by a carotid sulcus which lodges the internal carotid artery and cavernous sinus.
    3. The lateral margin of the carotid sulcus at its posterior end projects backward into tongue-shaped lingula.
    4. The lingula lies just above the posterior opening of the pterygoid canal.

Sphenoid Bone Superior Aspect

Sphenoid Bone Posterior Aspect

Sphenoid Bone Anterior Aspect

2. Sphenoidal Sinuses

  1. These are two large air spaces present in the body of the sphenoid.
  2. The two sinuses are separated by a septum and are rarely symmetrical.
  3. Relations
    1. Superiorly:
      1. Optic chiasma.
      2. Pituitary gland.
    2. Laterally
      1. Internal carotid artery.
      2. Cavernous sinus.
  4. Size
    1. Vertical height: 2 cm (a little less than 2 cm)
    2. Transverse breadth: 1.8 cm
    3. Anteroposterior depth: 2.1 cm (little more than 2 cm).
      • Note: For simplification, students may consider all the measurements approximately as 2 cm.
  5. Each sinus communicates with the spheno-ethmoidal recess.
  6. Development
    1. Sphenoidal sinus starts developing as nasal mucosal evagination during intrauterine life.
    2. These are in the form of minute cavities at birth.
    3. It develops to its adult size in adolescence.

Sphenoid Bone Wings

1. Greater wings

There are two greater wings, a right and a left. Each has three surfaces (cerebral, lateral, and orbital) and several margins.

  • Surfaces
    1. Cerebral Surface
      • It is concave. It forms part of the middle cranial fossa. It is related to the temporal lobe of the cerebrum. It possesses the following foramina.
        1. Foramen rotundum
          • It is situated in the anteromedial part. The maxillary nerve passes through it.
        2. Foramen ovale
          • It is situated posterolateral to foramen rotundum. It transmits:
          • Mandibular nerve.
          • Accessory meningeal artery.
          • Lesser petrosal nerve.
          • Emissary vein.
        3. Emissary sphenoidal foramen
          • It is an inconstant foramen present medial to foramen ovale. It transmits the emissary vein.
        4. Foramen spinosum
          • It is lateral to foramen ovale. It transmits:
          • Middle meningeal artery.
          • Nervus spinosus.
        5. Canaliculus innominatus
          • It is occasionally present between foramen ovale and foramen spinosum. If present, it transmits lesser petrosal nerve.
    2. Lateral Surface
      1. It is convex from above downwards.
      2. The infratemporal crest is an anteroposterior ridge that divides the lateral surface into upper temporal and lower infratemporal parts.
      3. The temporal surface forms part of the temporal fossa and gives origin to the temporalis muscle.
      4. The infratemporal surface forms the roof of the infratemporal fossa and gives origin to the upper head of the lateral pterygoid muscle. This surface possesses openings of foramen ovale and foramen spinosum.
      5. The spine of the sphenoid is a projection at the posterior end of the lateral surface. It shows the following relations and attachments:
        1. Tip gives attachment to spheno-mandibular ligament.
        2. Medially it is related to the chorda tympani nerve and auditory tube.
        3. Laterally it is related to the auriculotemporal nerve.
    3. Orbital Surface
      1. It is quadrilateral in shape.
      2. It forms the posterior part of the lateral wall of the orbit.
      3. Its upper serrated edge articulates with the orbital plate of the frontal bone.
      4. Its lateral serrated margin articulates with the zygomatic bone.
      5. Its inferior smooth border forms the posterolateral boundary of the inferior orbital fissure.
      6. Its medial sharp margin constitutes the lower boundary of the superior orbital fissure. A projection from this border provides attachment to a common tendinous ring.
      7. Below the medial end of the superior orbital fissure is a depressed area pierced by foramen rotundum.
  • Margins
    1. The tip of the greater wing is called the parietal margin. It articulates with the sphenoidal angle of the parietal bone at the pterion.
    2. The posterior margin of the greater wing extends from the body of the sphenoid to its spine. Its medial half forms the anterior boundary of the foramen lacerum and receives the opening of the pterygoid canal. Its lateral half articulates with the petrous temporal.
    3. The lateral margin extends forward from the spine to the tip of the greater wing. This is also called the squamosal margin because it articulates with the squamous part of the temporal bone.
    4. Medial to the tip there is a triangular rough area for the frontal bone.
    5. The anterior angle of the triangular area continues with a serrated margin (lateral margin of the orbital surface) which articulates with the zygomatic bone.

2. Lesser Wings

It is a triangular bone extending laterally from the anterosuperior part of the body. It consists of a tip, two roots (anterior and posterior), two surfaces (superior and inferior), and two borders (anterior and posterior).

  • Тір
    1. It is the lateral end of the lesser wing.
    2. It is situated near the lateral end of the superior orbital fissure.
  • Roots
    1. The lesser wing is connected to the body by anterior and posterior roots.
    2. The two roots enclose the optic canal which transmits the optic nerve and ophthalmic artery.
  • Surfaces
    1. Superior Surface
      • It forms the posterior part of the floor of the anterior cranial fossa.
    2. Inferior Surface
      • It forms the superior boundary of the superior orbital fissure and the posterior part of the orbital roof.
  • Borders
    1. Anterior border
      • It articulates with the posterior border of the orbital plate of the frontal bone.
    2. Posterior Border
      • It is free.
      • Its medial end forms the anterior clinoid process to which is attached the free margin of tentorium cerebelli.

3. Superior Orbital Fissure

  1. It is a triangular slit-like communication between the orbit and the middle cranial fossa.
  2. Boundaries
    • Medial: Body of sphenoid Apex: Frontal bone
    • Superior: Lesser wing of sphenoid.
    • Inferior: Greater wing of sphenoid.
  3. It transmits the following structures:
    • Structures that enter the orbit
      1. Upper and lower divisions of the oculomotor nerve.
      2. Trochlear nerve.
      3. Three branches (lacrimal, frontal, and nasociliary) of the ophthalmic division of the trigeminal nerve.
      4. Abducent nerve.
      5. Orbital branch of the middle meningeal artery.
      6. Sympathetic filaments.
    • Structures that appear from the orbit
      1. Superior and inferior ophthalmic veins.
      2. Recurrent meningeal branch of the lacrimal artery.

Pterygoid Processes

  • The pterygoid process on each side descends vertically downwards from the junction of the body and the greater wing of the sphenoid.
  • Each consists of a lateral and a medial pterygoid plate.
  • The plates unite anteriorly in the upper part to enclose a fossa called pterygoid fossa.
  • The plates are not united in the lower portion to form a pterygoid fissure which is filled by the pyramidal process of palatine bone.
  • The anterior surface of the pterygoid process forms the posterior boundary of the pterygopalatine fossa.
  • The anterior opening of the pterygoid canal is located in this region. Some details of the two pterygoid plates are as follows:

1. Lateral pterygoid plate

It has two surfaces (lateral and medial) and two borders (anterior and posterior).

  • Surfaces
    1. Lateral Surface
      • It forms the medial wall of the infratemporal fossa and gives origin to the lower head of the lateral pterygoid muscle.
    2. Medial Surface
      • It forms the lateral wall of the pterygoid fossa which gives origin to the deep head of the medial pterygoid muscle.
  • Borders
    1. Anterior Border
      • It forms the posterior boundary of the pterygomaxillary fissure.
    2. Posterior Border
      • It is free.

2. Medial Pterygoid Plate

It has two surfaces (lateral and medial) and two borders (anterior and posterior).

  • Surfaces
    1. Lateral surface
      • It forms the medial wall of the pterygoid fossa and is related to the tensor palate muscle.
    2. Medial surface
      1. It forms the lateral wall of the corresponding posterior nasal aperture.
      2. Vaginal process is a thin lamina projecting medially from its upper part under the body of the sphenoid.
      3. A groove on the anterior part of the undersurface completes the palatovaginal canal with the sphenoidal process of the palatine bone.
      4. This canal transmits the pharyngeal branch of the maxillary artery and the pharyngeal branch of the pterygopalatine ganglion.
      5. The vaginal process articulates medially with ala of the vomer and forms vomero-vaginal canal between the two. This canal transmits branches of pharyngeal nerves and vessels.
  • Borders
    1. Anterior border
      • It articulates with the posterior border of the perpendicular plate of the palatine bone.
    2. Posterior border
      1. At its upper end, it splits to enclose the scaphoid fossa which gives origin to the tensor palati muscle.
      2. Its upper end shows a small projection called the pterygoid tubercle which lies immediately below the posterior end of the pterygoid canal.
      3. Pharyngobasilar fascia is attached to its whole extent while the superior constrictor arises from its lower part only.
      4. A hook-like process at its lower end is called pterygoid hamulus. Tondon of tensor palati winds around this process. Superior constrictor and pterygomandibular raphe are also attached to it.
      5. An angular process projecting from the middle of this margin is called processus tubarius.
      6. The posterior border above this process is called the notch of the auditory tube. This process and notch support the medial end of the auditory tube.

Sphenoid Bone Ossification

  1. Sphenoid ossifies partly in the membrane and partly in cartilage.
  2. Parts ossifying in the membrane are as follows:
    • Greater wings except for their roots.
    • Pterygoid processes except pterygoid hamuli.
  3. Parts ossifying in cartilage are as follows:
    • Body of sphenoid.
    • Lesser wings.
    • Sphenoidal conchae.
    • Roots of greater wings.
    • Pterygoid hamuli.
  4. From an ossification point of view, the sphenoid is divided into presphenoidal and post-sphenoidal parts.
    1. The presphenoidal part is comprised of parts lying in front of tuberculum sellae, i.e. anterior part of the body, lesser wings, and sphenoidal conchae.
      1. Two centers appear for each of these components as follows:
      2. Anterior body-9th week of intrauterine life.
      3. Lesser wings-9th week of intrauterine life.
      4. Conchae-5th month of intrauterine life.
    2. Rest of the sphenoid is included in post sphenoidal part. Two centers appear for each of the following components of the post-sphenoidal part.
      • Sella turcica-4th month of intrauterine life.
      • Lingulae 4th month of intrauterine life. Greater wings (including lateral pterygoid plates)-8th week of intrauterine life.
      • Medial pterygoid plates-9th week of intrauterine life.
      • Hamuli-3rd month of intrauterine life.
  5. Fusions of different components of sphenoid take place as follows:
    1. Medial and lateral pterygoid plates fuse with each other at about 6th month of intrauterine life.
    2. The presphenoidal part of the body fuses with the postsphenoidal part of the body at about the 8th month of intrauterine life.
    3. At birth, the sphenoid is in three parts, a central part consisting of the body and lesser wings and two lateral parts, each consisting of the greater wing and the pterygoid process.
    4. Greater wing fuses with the body at about 1st year.
    5. Concha fuses with the ethmoidal labyrinth at about 4th year.
    6. Concha fuses with the body of the sphenoid before puberty.
    7. The body of the sphenoid fuses with the basilar part of the occipital bone at about the 25th year.

Sphenoid Bone Applied Anatomy

  1. In the anterior part of the hypophyseal fossa, there is occasionally a vascular foramen termed as craniopharyngeal canal. The canal sometimes extends inferiorly to the exterior of the skull and is said to mark the original position of Rathke’s pouch.
  2. Premature ossification of sutures between pre and post-sphenoidal parts and sphenoid and occipital bones is often observed in achondroplasia.
  3. Anomalous development of the pre-sphenoidal elements may lead to excessive separation of the two orbits (hypertelorism).
  4. Observation of the sella turcica and the hypophyseal fossa in radiographs is important clinically because they may reflect pathological changes such as a pituitary tumor or aneurysm of the internal carotid artery.
  5. Decalcification of the dorsum sellae is one of the signs of a generalized increase in intracranial pressure.
  6. The lateral wall of the optic canal is fractured during optic nerve decompression in the optic canal.
  7. A fracture of the sphenoid bone may lacerate the optic nerve resulting in blindness.
  8. Basilar fracture of the skull through the sphenoid bone may lacerate the internal carotid artery resulting in the carotid-cavernous fistula. This leads to pulsating exophthalmos.
  9. Collection of air in the cranial cavity (aerocele) may occur if the basilar fracture of the skull involves a sphenoidal sinus.
  10. Involvement of the pterygoid processes of the sphenoid is a constant feature in cases of Le Fort fractures of the mid-facial skeleton but the location of a fracture depends upon its type.
  11. In Le Fort 1 fracture, the lower 3rd of the pterygoid plates is involved while in Le Fort 3 fracture the roots of pterygoid plates are fractured.
  12. Large areas of the body and medial pterygoid plates are clothed in mucosa and, therefore, fractures of these parts of the sphenoid may open into the nasal cavity or sphenoidal sinus with potential risk of infection.

Vomer: Anatomy, Location, And Function Notes

Vomer

Vomer Terminology

‘Vomer’ is a Latin word. The term is used for the thin plate of bone between the nostrils.

Vomer Location

Vomer forms the posteroinferior part of the septum of the nose.

Vomer Left View

Vomer Features And Attachments

Vomer has got two surfaces (right and left) and four borders (superior, inferior, anterior, and posterior).

Vomer Surfaces

  1. It has small grooves for vessels.
  2. A large groove runs downwards and forwards. This is meant for nasopalatine nerve and vessels.

Vomer Borders

  • Superior Border
    1. It is thick.
    2. Two lateral projections (alae) enclose a deep furrow that fits over the rostrum of the sphenoid.
    3. The margin of ala intervenes between the body of the sphenoid and the vaginal process of the medial pterygoid plate. Under the surface of the ala forms a vomer-ovaginal canal with the vaginal process.
  • Inferior Border
    • It articulates with the nasal crest formed by the maxillae and palatine bones.
  • Anterior Border
    1. It is the longest border.
    2. Its upper half articulates with the posterior border of the perpendicular plate of the ethmoid bone.
    3. Its lower half is attached to septal cartilage.
  • Posterior Border
    1. It is free.
    2. It is situated between two posterior nasal apertures (choanae).

Vomer Le Fort Fractures

Vomer Ossification

  1. Vomer develops by ossification of the membrane covering the median septal part of the cartilaginous nasal capsule.
  2. One center of ossification appears on each side of the cartilage at about the 8th week of intrauterine life. giving rise to two bony plates separated by a cartilage.
  3. Two bony plates fuse with each other in the lower part at about the 12th week of intrauterine life.
  4. The cartilaginous plate is gradually absorbed allowing the fusion of two bony plates which proceed upwards from below. Fusion is completed at puberty.

Vomer Applied Anatomy

  1. The vomer is paper thin and does not resist much force responsible for the fracture.
  2. The vomer is involved in all three types of Le Fort fractures of the mid-facial skeleton.
  3. Vomer receives adequate blood supply from periosteal arteries and therefore all the fragments of fractured bone retain a periosteal blood supply.
  4. A transverse fracture of the vomer due to a direct blow on the nose can lead to deviation of the nasal septum (DNS).
  5. The vomer is clothed in mucosa over large areas of its surfaces, and therefore, its fracture opens into the nasal cavity with a potential risk of infection.
  6. Vomer may be deviated from the median plane as a result of birth injury or a congenital malformation.
  7. In case of severe deviation, the nasal septum comes into contact with the lateral wall of the nasal cavity. Surgical repair (submucosal resection-SMR) is usually necessary to correct the deviation.

Vomer Vomerovaginal And Palatovaginal Canals

Nasal Conchae: Anatomy, Structure And Function Notes

Inferior Nasal Conchae

Inferior Nasal Conchae Terminology

‘Concha’ is a Latin word that means ‘shell’. Conchae (superior, middle, and inferior) are bracket-like projections of thin (like eggshell) bones from the lateral wall of the nose.

Inferior Nasal Conchae Location

An inferior concha is an independent bone whose long axis occupies the whole length of the lower part of the lateral wall of each half of the nasal cavity.

Inferior Nasal Conchae Features And Attachments

Each inferior concha has two ends (anterior and posterior), two surfaces (medial and lateral), and two borders (superior and inferior).

Inferior Nasal Conchae Ends

  1. Anterior End
    • It is pointed and directed forward.
  2. Posterior End
    • It is directed backward and is more pointed and tapering.

Inferior Nasal Conchae Surfaces

  • Medial Surface
    1. It is convex.
    2. It has numerous apertures and grooves for vessels.
  • Lateral Surface
    1. It is concave.
    2. It forms the medial wall of the inferior meatus of the nose.

Inferior Nasal Conchae Right Inferior Concha Medial Aspect

Inferior Nasal Conchae Right Inferior Concha Lateral Aspect

Inferior Nasal Conchae Borders

1. Superior Border

    1. It is thin and irregular.
    2. It is divided into three parts:
  • Anterior Part: This articulates with the conchal crest of the maxilla.
  • Posterior Part: This articulates with the conchal crest of the palatine bone.
  • Middle Region: This part possesses three processes which are as follows from anterior to posterior:
    1. Lacrimal Process: It is an upward projection to articulate the descending process of the lacrimal bone.
    2. Maxillary Process: It is a curved downward projection that articulates with the nasal surface of the maxilla and the lower part of the anterior border of the perpendicular plate of the palatine bone.
    3. Ethmoidal process: It is an upward projection to articulate with the uncinate process of the ethmoid.

2. Inferior Border

  • It is free.
  • It is thick.

Inferior Nasal Conchae Ossification

1. It develops from the lowest part of the lateral region of the cartilaginous nasal capsule.

2. The center of ossification appears during the 5th month of intrauterine life.

Inferior Nasal Conchae Applied Anatomy

Inferior nasal concha is at great risk in cases of mid-facial injuries.

  1. Inferior concha receives adequate blood supply from periosteal arteries and, therefore, all the fragments of the fractured bone retain a periosteal blood supply.
  2. Inferior concha is clothed in nasal mucosa over large areas of its surfaces and, therefore, the fractures usually open to the nasal cavity with potential risk of infection.
  3. Infracture of the inferior concha is sometimes needed during the management of congenital lacrimal defects.

Inferior Nasal Conchae Infracture Of Inferior Concha

Lacrimal Bone: Anatomy, Borders And Function Notes

Lacrimal Bones

Lacrimal Bones Terminology

‘Lacrimal’ is a Latin word which means ‘tear’. The bone is so named because of its relation with the tear sac.

Lacrimal Bones Peculiarities

  1. It is most fragile among the cranial bones.
  2. It is the smallest of the cranial bones.

Lacrimal Bones Location

  1. There are two lacrimal bones.
  2. Each lacrimal bone is located in the anterior part of the medial wall of the orbit.
  3. It also contributes to the middle meatus of the nose.

Lacrimal Bones Features And Attachments

Lacrimal bone is rectangular in shape. It has two surfaces (medial and lateral) and four borders (anterior, posterior, superior, and inferior).

Lacrimal Bones Surfaces

1. Medial Surface

  • It is also called the nasal surface.
  • Its anteroinferior part contributes partly to the middle meatus of the nose.
  • Its posterosuperior part articulates with the ethmoid and completes a few anterior ethmoidal air cells.

Lacrimal Bones Right Lacrimal Bone Medial Surface

2. Lateral Surface

  • It is also known as the orbital surface.
  • It is divided into anterior and posterior parts by a vertical crest called the posterior lacrimal crest.
  • The anterior part is grooved and forms the posterior half of the floor of the lacrimal groove.
  • The anterior half of the lacrimal groove is formed by the frontal process of the maxilla. The groove lodges the lacrimal sac.
  • The portion behind the posterior lacrimal crest is smooth and forms part of the medial wall of the orbit.
  • The lower end of the posterior lacrimal crest projects forward as the lacrimal hamulus.
  • It articulates with the maxilla to complete the upper end of the nasolacrimal canal.
  • The posterior lacrimal crest provides attachment to the lacrimal fascia.
  • The crest and small area of the lateral surface immediately behind it give origin to the lacrimal part of the orbicularis oculi muscle.
  • The medial wall of the groove projects downwards in a descending process.
  • This process articulates with the lips of the nasolacrimal groove of the maxilla and the lacrimal process of the inferior concha to complete the bony canal for the nasolacrimal duct.

Lacrimal Bones Right Lacrimal Bone Lateral Surface

Lacrimal Bones Borders

  1. Anterior Border
    • It articulates with the frontal process of the maxilla.
  2. Posterior Border
    • It articulates with the orbital plate of the ethmoid.
  3. Superior Border
    • It articulates with the nasal notch of the frontal bone.
  4. Inferior Border
    • It articulates with the orbital surface of the maxilla.

Lacrimal Bones Ossification

Lacrimal bone ossifies in membrane.

2. A single center of ossification appears in the mesenchyme around the cartilaginous nasal capsule.

3. The center appears at about the 12th week of intrauterine life.

Lacrimal Bones Applied Anatomy

  1. A severe impact on the nasal bridge may involve the lacrimal bone and damage the lacrimal passage.
  2. Lacrimal bone is included by clinicians in the central portion of the middle 3rd facial skeleton.
  3. All the bones of the middle 3rd facial skeleton receive adequate blood supply from periosteal arteries and, therefore, all the fragments of fractured bone retain a periosteal blood supply.
  4. Lacrimal bone is involved in Le Fort 3 fracture.
  5. Since the anteroinferior part of the nasal surface of the lacrimal bone is covered with nasal mucosa, the fracture of the bone may open into the nasal cavity with the potential risk of infection.
  6. To reach the medial wall of the optic canal during a surgical procedure called optic nerve decompression, most of the bones of the medial wall of the orbit (including the lacrimal bone) are fractured.
  7. Lacrimal bone is very fragile, therefore extra precautions should be taken to avoid trauma during surgery of the lacrimal system.
  8. In some of the cases of obstruction of the lacrimal sac or nasolacrimal duct, dacryocystorhinostomy is performed.
  9. In this operation, an artificial passage is made for drainage into the nasal cavity, by breaking the lacrimal bone.

Parietal bone: Anatomy, Borders and Surfaces

Parietal Bones Terminology

The word parietal is derived from the Latin word ‘paries’ which means ‘wall’, because two parietal bones form a large part of the walls of the calvaria.

Parietal Bones Side Determination

  1. Keep the bone by the side of your own cranial vault in such a way that the outer surface is convex and the inner surface is concave.
  2. Inferior (squamosal) border is concave.
  3. The anteroinferior angle is prominent and has a vascular and narrow groove on its inner aspect.
  4. The posteroinferior angle has a shallow and wide groove for the sigmoid sinus on its inner aspect.

Parietal Bones Features And Attachments

1. Parietal Bones Surfaces

It has two surfaces, external and internal.

  • External Surface
    • It is relatively smooth.
    • The most prominent part of this surface is called parietal tuberosity or eminence.
    • There are two curved lines running anteroposteriorly. These are called superior and inferior temporal lines.
    • The superior temporal line gives attachment to temporal fascia while the area below the inferior temporal line gives attachment to the temporalis muscle.
    • The area above the superior temporal line is covered by galea aponeurotica.
    • A foramen may be present near the posterior part of the sagittal border. This is called parietal foramen. It transmits the emissary vein.
  • Internal Surface
    • It is concave and exhibits elevations and depressions for cerebral sulci and gyri respectively.
    • Near the sagittal border, there is a longitudinal half groove (to be completed with that of the opposite side) for the superior sagittal sinus. The margins of the groove provide attachment to falx cerebri
    • Grooves for the branches of middle meningeal vessels are present at the anteroinferior angle and at the middle of the lower border of the bone.
    • Adjacent to the groove for the superior sagittal sinus there are deep irregular pits (granular foveolae) produced by arachnoid granulations.
    • The bone is grooved near the posteroinferior angle by the sigmoid sinus.

Parietal Bones Right Parietal Bone External Surface

Parietal Bones Right Parietal Bone Internal Surface

2. Parietal Bones Borders

It has four borders, superior, inferior, anterior, and posterior.

  • Superior Border
    • This is also called the sagittal border.
    • It articulates with a similar border of opposite sides to form a sagittal suture.
  • Inferior Border
    • This is also called the squamosal border.
    • It articulates with the following three bones from anterior to posterior:
      • Greater wing of the sphenoid.
      • Squamous part of temporal.
      • Mastoid portion of temporal.
  • Anterior Border
    • This is also called the frontal border.
    • It articulates with the frontal bone to form a coronal suture.
  • Posterior Border
    • This is also called the occipital border.
    • It articulates with the squamous part of the occipital bone to form a lambdoid suture.

3. Parietal Bones Angles

The parietal bone has four angles (frontal, sphenoidal, occipital, and mastoid).

  • Frontal Angle
    • This is also called the anterosuperior angle.
    • It corresponds to bregma, i.e. the junction of coronal and sagittal sutures.
  • Sphenoidal Angle
    • This is also called an anteroinferior angle.
    • It corresponds to pterion, i.e. a small area enclosing four bones (frontal, temporal, parietal, and greater wing of sphenoid).
  • Occipital Angle
    • This is also called the posterosuperior angle.
    • It corresponds to lambda, i.e. junction of sagittal and lambdoid sutures.
  • Mastoid Angle
    • This is also called posteroinferior angle.
    • It corresponds to asterion, i.e. small area enclosing three bones, parietal, temporal, and occipital.

Parietal Bones Ossification

  1. Parietal bones ossify in the membrane.
  2. Each ossifies from two centers which appear at parietal tuberosity at about the 7th week of intrauterine life.
  3. The centers soon fuse with each other and then the ossification spreads radially.
  4. Angles are the parts last to be ossified explaining the existence of a fontanelle at each angle before the ossification is completed.

Parietal Bones Age Changes

  • At birth
    • Temporal lines are present at quite a lower level.
  • Adult
    • Higher and permanent positions of temporal lines are reached only after the eruption of permanent molar teeth.

Parietal Bones Applied Anatomy

  1. Occasionally the parietal bone is divided into upper and lower parts by an anteroposterior suture. The condition may be confused with fracture radiologically.
  2. The latter can be ruled out easily because the anomalous parietal suture is usually bilateral.
  3. Parietal bones are loosely attached to the adjacent bones at sutures during the intrauterine period allowing moulding (change in shape of calvaria) at the time of childbirth.
  4. Calvaria returns to normal shape within a few days after birth.
  5. Parietal bones undergo remodeling to allow enlargement of calvaria during childhood. This is only possible because of their loose attachments to the adjacent bones.
  6. Granular foveolae are more numerous and marked in aged parietal bones. This fact is of great medical importance.
  7. The regenerating capacity of the parietal bone is negligible due to the lack of a cambium layer in the periosteum.
  8. In neonates, the parietal bone is pliable and soft, and, therefore, a depressed fracture (pond fracture) is like a dimple.
  9. In adults such fractures are produced by direct blows and always show an irregular line of fracture at the periphery of the depressed area. The depression of the inner table forms the lowest limit of the depressed area also
  10. Almost invariably all fractures the known as apex.
  11. A crack in the inner table of the parietal bone may damage a large diplomatic vein and produce a small epidural hematoma. parietal bone in children is associated with rupture of the dura mater.
  12. In adults, the parietal bone shows a fissured or linear fracture if the force is transmitted to this bone from frontal or occipital blows.

Parietal Bones A Depressed Fracture Of Parietal Bone In Adult