CBSE Class 10

These NCERT Solutions for Class 10 Maths Chapter 12 Areas Related to Circles Questions and Answers are prepared by our highly skilled subject experts.

NCERT Solutions for Class 10 Maths Chapter 12 Areas Related to Circles Exercise 12.2

Question 1.
Find the area of a sector of a circle with radius 6 cm if angle of the sector is 60°.
Solution:
Radius of the sector (r) = 6 cm
Central angle of the sector = 60°
We know that

Therefore, the area of required circle is \(\frac { 132 }{ 7 }\) cm²

Question 2.
Find the area of a quadrant of a circle whose circumference is 22 cm.
Solution:
Angle of quadrant 0 = 90°
Circumference of the circle = 2πr
22 = 2πr
r = \(\frac { 11 }{ π }\)cm

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:
Angle made by minute hand in 60 minute is
∴ Angle made by minute hand in 1 minute is = \(\frac{360^{\circ}}{60^{\circ}}\) = 6°

Length of minute of hand (r) = 14 cm
We know that

Area swept by minute hand in 5 minutes is \(\frac { 153 }{ 3 }\) cm²

Question 4.
A chord of a circle of radius 10 cm subtends a right angle at the centre. Find the area of the corresponding:
(i) minor segment
(ii) major segment (Use π = 3.14)
Solution:
Given: radius of the circle = 10 cm
Angle subtended by chord at centre = 90°
(i)

(ii) Area of the major segment = Area of the circle – Area of the minor segment
= πr² – 28.5 = 3.14 x 10 x 10-28.5
= 314-28.5 = 285.5 cm²

Question 5.
In a circle of radius 21 cm, an arc subtends an angle of 60° at the centre. Find:
(i) length of the arc.
(ii) area of the sector formed by the arc.
(iii) area of the segment formed by the corresponding chord.
Solution:
We have,
Radius of the circle = 21 cm
Angle at the centre = 60°
(i) We know that

Therefore, length of arc AB = 22 cm.

(iii) Area of segment = Area of sector – Area of equilateral ∆OAB

Therefore, area of sector made by arc AB = is 231 cm².

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 \(\sqrt{3}\) = 1.73)

Solution:
Radius of the circle = 15 cm
Angle subtended by chord at centre = 60°
Area of the sector = \(\frac{\pi r^{2} \theta}{360^{\circ}}\) = 3.14 x \(\frac{15 \times 15 \times 60^{\circ}}{360^{\circ}}\) = 117.75 cm²
Area of the triangle formed by radii and chord = \(\frac { 1 }{ 2 }\)r²θ
= \(\frac { 1 }{ 2 }\)(15)² sin 60° = \(\frac { 1 }{ 2 }\) x 15 x 15 x \(\frac{\sqrt{3}}{2}\) = 97.31 cm²
Area of the minor segment = Area of the sector – Area of the triangle formed by radii and chord
= 117.75 – 97.31 = 20.44 cm²
Area of the circle = πr² = 3.14 x 15 x 15 = 706.5 cm²
Area of the circle – Area of the minor segment
= 706.5 – 20.44 = 686.06 cm²
Therefore, area of major segment is 686.0625 cm²

Question 7.
A chord of a circle of the 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 \(\sqrt{3}\) = 1.73).
Solution:
Construct a circle C with radius 12 cm and centre O

Area of the corresponding segment = Area of sector – Area of ∆AOB = 150.72 – 62.28 cm²
= 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 (see figure). Find
(i) the area of that part of the field in which the horse can graze.
(ii) the increase in the grazing area if the rope were 10 m long instead of 5 m. (Use π = 3.14)

Solution:
(i) Length of the rope = Radius of the sector grazed by horse = 5 m
Here, angle of the sector = 90°

Hence, the area of the part of the field which is grazed by horse is 19625 m².

(ii) Now, radius = 10m
Angle = 90°

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

Find:
(i) the total length of the silver wire required.
(ii) the area of each sector of the brooch.
Solution:

One diameter of the circle in 35 mm long The length of 5 diameters = 5 x 35 = 175 mm
The required length of the silver wire = circumference of circle + length of 5 diameters
= 110 + 175 = 285 mm

(ii) Let O be the centre of circle and radius is

The angle made by the diameters of one part

Hence the area of each sector of the brooch is \(\frac { 385 }{ 4 }\) mm²

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

Solution:
Let O be the centre of the umbrella and the radius is 45 cm
The angle between two consecutive ribs \(\frac { 360° }{ 8 }\)
Area between two consecutive ribs
= \(\frac{360^{\circ}}{360^{\circ} \times 8} \times \frac{22}{7} \times(45)^{2}\)
= \(\frac{22275}{28} \mathrm{~cm}^{2}\)

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: length of blade of wiper = radius of sector sweep by blade = 25 cm
Area cleaned by each sweep of the blade = area of sector sweep by blade
Angle of the sector formed by blade of wiper = 115°

Hence, the total area cleaned at each sweep is \(\frac { 158125 }{ 126 }\) cm².

Question 12.
To warn ships for underwater rocks, a lighthouse spreads a red coloured light over a sector of angle 80° to a distance of 16.5 km. Find the area of the sea over which the ships are warned. (Use π = 3.14)
Solution:
Angle of the sector = 80°
Distance covered = 16.5 km
Radius of the sector formed = 16.5 km

Hence the area of sea over which the ships are warned is 189.97 km².

Question 13.
A round table cover has six equal designs as shown in the figure. 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 \(\sqrt{3}\) = 1.7)

Solution:

Area of the design = Area of sector AOB – Area of ∆AOB
= 410.67 – 333.20
= 77.47
There are six designs in the circle
Area of six designs = 77.47 x 6
= 464.82 cm²
The cost of making the design at the rate of 0.35 per cm²
₹ (464.82 x 0.35) = ₹ 162.68
Hence the required cost of making the design is ₹ 162.68

Question 14.
Tick the correct answer in the following: Area of a sector of angle p (in degrees) of a circle with radius R is
(a) \(\frac{p}{180^{\circ}}\) × 2πR
(b) \(\frac{p}{180^{\circ}}\) × πR²
(c) \(\frac{p}{360^{\circ}}\) × 2πR
(d) \(\frac{p}{720^{\circ}}\) × 2πR²
Solution:
Sector angle is p in degrees
Radius of the circle = R
Area of the sector = \(\frac{\pi \mathrm{R}^{2} p}{361^{6}}\) = \(\frac{\left(\pi R^{2} p\right) 2}{720^{\circ}}\)
= \(\frac{p}{720^{\circ}}\) × 2πR²
Hence (D) is the correct answer.

These NCERT Solutions for Class 10 Maths Chapter 12 Areas Related to Circles Questions and Answers are prepared by our highly skilled subject experts.

NCERT Solutions for Class 10 Maths Chapter 12 Areas Related to Circles Exercise 12.1

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

Given: radius of 1^st circle (R₁) = 19 cm
∴ Circumference of 1^st circle = 2πR₁ = 2π(19) cm
Radius of 2^nd circle (R₂) = 9 cm
∴ Circumference of 2^nd circle = 2πR₂ = 2π(9) cm
Let radius of 3^rd circle be R₃
Circumference of 3^rd circle = 2πR₃
According to question,
2πR₁ + 2πR₂ = 2πR₃
⇒ 2π(R₁ + R₂) = 2πR₃
⇒ R₁ + R₂ = R₃
⇒ 19 + 9 = R₃
⇒ R₃ = 28 cm
So, the radius of the circle whose circumference is equal to the two circles of radius 19 cm is 28 cm.

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

Given: radius of 1^st circle (R₁) = 8 cm
Area of 1^st circle = πR₁² = π(8)²cm²
Radius of 2^nd circle (R₂) = 6 cm
Area of 2^nd circle = πR₂² = π(6)² cm²
Let radius of 3^rd circle be R₃
Area of 3^rd circle = πR₃²
According to question,
πR,² + πR₂² – πR₃²
⇒ R₁² + R₂² = R₃² 
⇒ (8)² + i6)² – R₃²
⇒ 64 + 36 = R₃² ⇒ R₃=  \( \sqrt{100} \) = 10 cm
Therefore, radius of the required circle is 10 cm.

Question 3.
The figure 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 Gold score is 21 cm and each of the other bands is 10.5 cm wide. Find the area of each of the five scoring regions.

Solution:
Diameter of region representing Gold = 21 cm
Radius of Gold = \(\frac { 21 }{ 2 }\) cm = 10.5cm
Area of region Gold = 2πr²
= \(\frac { 22 }{ 2 }\) x (10.5)²
= 346.5 cm²
The Red band is 10.5 wide
Radius of (Red + Gold) = 10.5 + 10.5 cm
= 21 cm
Area of (Red + Gold) = πr² = \(\frac { 22 }{ 2 }\)
= 1386 cm²
Area of Red band =Area of (Red + Gold) – Area of Gold
= 1386 – 346.5 cm
= 1039.5 cm²
Again,
Radius of (Gold + Red + Blue)
= 21 + 10.5 cm = 31.5 cm
Area of (Gold + Red + Blue)
= πr²
= \(\frac { 22 }{ 2 }\) x 31.5 x 31.5
= 3118.5 cm²
Are of Blue Band = Area of (Gold + Red + Blue) – Area of (Gold + Red)
= 3118.5 – 1386
= 1732.5 cm²
Again,
Radius of (Gold + Red + Blue + Black) = 31,5 + 10.5 = 42 cm
Area of (Gold + Red + Blue + Black) = πr²
= \(\frac { 22 }{ 2 }\) – (42)²
= \(\frac { 22 }{ 2 }\) x 42 x 42 cm²
= 5544 cm²
Area of Black Band = Area of (Gold + Red + Blue + Black) – Area of (Gold + Red + Blue)
= 5544 – 3118.5 cm²
= 2425.5 cm²
Again,
Radius of (Gold + Red + Blue + Black + White)
= 42 + 10.5
= 52.5
Area of (Gold + Red + Blue + Black + White)
= πr²
= \(\frac { 22 }{ 2 }\) x (52.5)²
= \(\frac { 22 }{ 2 }\) x 52.5 x 52.5 cm²
= 8662.5 cm²
Area of White Band = Area of (Gold + Red + Blue + White) – Area of (Gold + Red + Blue + Black)
= 8662.5 – 5544 cm²
= 3118.5 cm²

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:
Distance travelled by the wheel in one revolution
= π x diameter of the wheel
= \(\frac { 22 }{ 2 }\) x 80
Total distance travelled by the wheel in one minute
= \(\frac{66 \times 1000 \times 100}{60}\) cm
∴ Number of revolutions made by the wheel in one minute
\(\frac{66 \times 1000 \times 10}{60 \times \frac{22}{7} \times 80}\) = \(\frac{66 \times 1000 \times 100 \times 7}{60 \times 22 \times 80}\) = 437.5
∴ Number of revolutions made by the wheel m 10 minutes
= (437.5 x 10) = 4375

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
Solution:
Let radius of the circle = r units
Perimeter of the circle = 2πr
Area of the circle = πr²
According to question,
Perimeter of the circle = Area of the circle
⇒ 2πr = πr²
⇒ r = 2 units
Hence, option (a) is correct.

These NCERT Solutions for Class 10 Maths Chapter 11 Constructions Ex 11.1 Questions and Answers are prepared by our highly skilled subject experts.

NCERT Solutions 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 an acute angle BAX on base AB. Mark the ray as AX.
3. Locate 13 points A₁, A₂, A₃, …… , A₁₃ on the ray AX so that AA₁ = A₁A₂ = ……… = A₁₂A₁₃
4. Join A₁₃ with B and at A₅ draw a line ∥ to BA₁₃, i.e. A₅C. The line intersects AB at C.

On measure AC = 2.9 cm and BC = 4.7 cm.
Then AC : CB = 5 : 8
Since A₃C is parallel to A₁₃B therefore

This show that C divides AB in the ratio 5

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:

First we draw line AB 6 cm and then cut an arc AC = 4 cm. After that cut an another are BC = 5 cm. Join A to C and B to C. We find a AABC.

1. Draw ray AX making an acute angle with AB.
2. Locate points A₁, A₂, A₃, A₄, A₅ on AX so that AA₁ = A₁A₃, = A₂A₃
3. Join BA₃.
4. Join A₂B’ such that A₂B’ || A₃B and (∠AA₃B = ∠AA₂B’)
5. Through B draw a ray B’C || BC’ and ∠ABC – ∠AB’C.

Hence ABC is the required triangle.

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 ΔABC with AB = 5 cm, BC = 7 cm and AC = 6 cm.
2. Draw an acute angle CBA below BC at point B.
3. Mark the ray BX as B₁, B₂, B₃, B₄, B₅, B₆ and B₇ such that BB₁= B₁B₂ = B₂B₃ = B₃B₄ = B₄B₅ = B₅B₆ = B₆B₇.
4. Join B₅ to C.
5. Draw B₇C’ parallel to B₅C, where C’ is a point on extended line BC.
6. Draw A’C’ ∥ AC, where A’ is a point on extended line BA.

∴ A’BC’ is the required triangle.

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 base AB = 8 cm.
2. Draw perpendicular bisector of AB. Mark CD = 4 cm, on ⊥ bisector where D is mid-point on AB.
3. Draw an acute angle BAX, below AB at point A.
4. Mark the ray AX with A₁, A₂, A₃ such that AA₁ =A₁A₂ = A₂A₃
   
5. Join A₂ to B. Draw A₃B’ ∥ A₂ B, where B’ is a point on extended line AB.
6. At B’, draw B’C’ 11 BC, where C’ is a point on extended line AC.

∴ ∆AB’C’ is the required triangle.

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

1. Draw a line segment BC = 6 cm and at point B draw an ∠ABC = 60°.
2. Cut AB = 5 cm. Join AC. We obtain a ΔABC.
3. Draw a ray BX making an acute angle with BC on the side opposite to the vertex A.
4. Locate 4 points A₁, A₂, A₃ and A₄ on the ray BX so that BA₁ = A₁A₂ = A₂A₃ = A₃A₄.
5. Join A₄ to C.
6. At A₃, draw A₃C’ ∥ A₄C, where C’ is a point on the line segment BC.
7. At C’, draw C’A’ ∥ CA, where A’ is a point on the line segment BA.

∴ ∆A’BC’ is the required triangle.

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 ∆ABC.
Solution:
In ∆ABC, ∠A + ∠B + ∠C = 180°
⇒ 105° + 45° + ∠C = 180°
⇒ 150° + ∠C = 180°
⇒ ∠C = 30°
Steps of Construction:

1. Draw a line segment BC = 7 cm. At point B, draw an ∠B = 45° and at point C, draw an ∠C = 30° and get ΔABC.
2. Draw an acute ∠CBX on the base BC at point B. Mark the ray BX with B₁, B₂, B₃, B₄, such that BB₁ = B₁B₂ = B₂B₃ = B₃B₄
3. Join B₃ to C.
4. Draw B₄C’ ∥ B₃C, where C’ is point on extended line segment BC.
5. At C’, draw C’A’ ∥ AC, where A’ is a point on extended line segment BA.

∴ ∆A’BC’ is the required triangle.

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 \(\frac { 5 }{ 3F }\) times the corresponding sides of the given triangle.
Solution:
Steps of Construction:

1. Draw a right angled ∆ABC with AB = 4 cm, AC = 3 cm and ∠A = 90°.
2. Make an acute angle BAX on the base AB at point A.
3. Mark the ray AX with A₁, A₂, A₃, A₄, A₅ such that AA₁ = A₁A₂ = A₂A₃ = A₃A₄ = A₄A₅.
4. Join A₃B. At A₅, draw A₅B’ ∥ A₃B, where B’ is a point on extended line segment AB.
5. At B’, draw B’C’ ∥ BC, where C’ is a point on extended line segment AC.

∴ ∆AB’C’ is the required triangle.

These NCERT Solutions for Class 10 Maths Chapter 10 Circles Ex 10.2 Questions and Answers are prepared by our highly skilled subject experts.

NCERT Solutions for Class 10 Maths Chapter 10 Circles Exercise 10.2

Question 1.
From a point Q, the length of the tangent to a circle is 24 cm and the distance of Q from the centre is 25 cm. The radius of the circle is
(a) 7 cm Sol.
(b) 12 cm
(c) 15 cm
(d) 24.5 cm
Solution:

Therefore, radius of the circle is 7 cm
So, option (A) of the give question is right.

Question 2.
In figure, if TP and TQ are the two tangents to a circle with centre O so that ∠POQ = 110°, then ∠PTQ is equal to
(a) 60°
(b) 70°
(c) 80°
(d) 90°
Solution:

∠OPT = 90°
∠OQT = 90°
∠POQ = 110°
TPOQ is a quadrilateral,
∴ ∠PTQ + ∠POQ = 180° ⇒ ∠PTQ + 110° = 180°
⇒ ∠PTQ = 180°- 110° = 70°
Hence, correct option is (b).

Question 3.
If tangents PA and PB from a point P to a circle with centre O are inclined to each other at angle of 80°, then ∠POA is equal to
(a) 50°
(b) 60°
(c) 70°
(d) 80°
Solution:
In AOAP and AOBP
OA = OB [Radii]
PA = PB

[Lengths of tangents from an external point are equal]
OP = OP [Common]
∴ ∆OAP ≅ ∆OBP [SSS congruence rule]
∠AOB + ∠APB = 180° ⇒ ∠AOB + 80° = 180°
⇒ ∠AOB = 180° – 80° = 100°
From eqn. (i), we get
⇒ ∠POA = \(\frac { 1 }{ 2 }\) x 100° = 50°
Hence, correct option is (a)

Question 4.
Prove that the tangents drawn at the ends of a diameter of a circle are parallel.
Solution:
AB is a diameter of the circle, p and q are two tangents.
OA ⊥ p and OB ⊥ q
∠1 = ∠2 = 90°
⇒ p || q ∠1 and ∠2 are alternate angles]

Question 5.
Prove that the perpendicular at the point of contact to the tangent to a circle passes through the centre.
Solution:
XY tangent to the circle C(0, r) at B and AB ⊥ XY. Join OB.
∠ABY = 90° [Given]
∠OBY = 90°
[Radius through point of contact is perpendicular to the tangent]
∴ ∠ABY + ∠OBY = 180° ⇒ AB Oiscollinear
∴ AB passes through centre of the circle.

Question 6.
The length of a tangent from a point A at distance 5 cm from the centre of the circle is 4 cm. Find the radius of the circle.
Solution:
OA = 5 cm, AP = 4 cm OP = Radius of the circle
∠OPA = 90° [Radius and tangent are perpendicular]

Question 7.
Two concentric circles are of radii 5 cm and 3 cm. Find the length of the chord of the larger circle which touches the smaller circle.
Solution:
Radius of larger circle = 5 cm Radius of smaller circle = 3 cm
OP ⊥ AB
[Radius of circle is perpendicular to the tangent]
AB is a chord of the larger circle

Question 8.
A quadrilateral ABCD is drawn to circumscribe a circle (see figure). Prove that AB + CD = AD + BC.
Solution:
AP = AS … (i)
[Lengths of tangents from an external point are equal]
BP = BQ … (ii)
CR = CQ … (iii)
DR = DS … (iv)

Adding equations (i), (ii), (iii) and (iv), we get
AP + BP + CR + DR = AS + BQ + CQ + DS
⇒ (AP + BP) + (CR + DR) = (AS + DS) + (BQ + CQ)
⇒ AB + CD = AD + BC
Hence proved.

Question 9.
In figure, XY and X’Y’ are two parallel tangents to a circle , x with centre O and another tangent AB with point of contact C intersecting XY at A and X’Y’ at B. Prove that ∠AOB = 90°.

Solution:
To Prove : ∠AOC = 90°
Join OC
XY and X’Y’ are two tangents
XY || X’Y’ (given) and AB is transversal … (i)
∠PAC + ∠QBC = 180° (Sum of int ∠s)
In ∆PAO and ∆CAO, we have
PA = AC (Tangent drawn from exterior point)
AO = AO (common)
PO = QC (radii of same circle)
∆ ∆PAO ≅ ∆CDO
⇒ ∠1 = ∠2
Similarly ∠3 = ∠4
Now, ∠PAC + ∠QBC = 180°
⇒ ∠1 + ∠2 + ∠3 + ∠4 = 180°
[∵ ∠1 = ∠2 and ∠4 = ∠3]
⇒ 2(∠2 + ∠3) = 180°
or ∠2 + ∠3 = 90°
Now, In ∆ OAB,
∠AOB + ∠2 + ∠3= 180° [put ∠2 + ∠3 = 90°]
or ∠AOB+ 90°= 180°
⇒ ∠AOB = 90°

Question 10.
Prove that the angle between the two tangents drawn from an external point to a circle is supplementary to the angle subtended by the line segment joining the points of contact at the centre.

Solution:
Given : Two tangents PA and PB are drawn from the point P to the circle with centre O. A and B are the points of contact of two tangents PA and PB respectively.
To Prove : ∠APB + ∠AOB = 180°
Construction: Join OA and OB
Proof : Since the tangent PA is drawn to the circle at A with centre O, we have;
OA ⊥ PA ⇒ ∠OAP = 90°
Similarly, since the tangent PB is drawn to the circle at B with centre O. we have,
OB ⊥ PB ⇒ OBP = 90°
We know the sum of four angles of a quadrilateral is 360°
Sc, in the quadrilateral, OA PB, we have
∠OAP + ∠APB + ∠OBP + ∠AOB = 360°
⇒ ∠APB + ∠AOB = 360° (∠OAP + ∠OBP) = 360° – 180°
⇒ ∠APB + ∠AOB = 180° Hence Proved.

Question 11.
Prove that the parallelogram circumscribing a circle is a rhombus.
Solution:
Given: ABCD is a || gm AB, BC, CD and DA are touching a circle.
To Prove: AB = BC = CD = DA
Proof : Since the length of two tangents drawn from an external point to a circle are equal, we have

AP = AS, BP = BQ, CR = CQ and DR = DS
AB + CD = AP + BP + CR + DR
AD + BC = AS + BQ + CQ + DS
= AS + DS + BQ + CQ
= AD + BC
⇒ AB + CD = AD + BC
⇒ 2AB = 2AD
w AB = AD
But AB= CD and BC = AD
AB = BC = CD = DA
Hence || gm ABCD is a rhombus.

Question 12.
A triangle ABC is drawn to circumscribe a circle of radius 4 cm such that the segments BD and DC into which BC is divided by the point of contact D are of lengths 8 cm and 6 cm respectively (see figure). Find the sides AB and AC.

Solution:
Let the sides AB, BC and AC touch the in circle at E, D and F respectievly. Join the centre O of the circle with A, B, C, D, E and F.
The point D divide BC in two parts CD = 6 cm and BD = 8 cm
Since tangent to a circle from an external point are equal CD = CF = 6 cm and DB = BE = 8 cm.

AF = AE = x cm (say)
OD= OE = OF = 4 [radii of the incircle]
Now, Area of ∆AOC = \(\frac { 1 }{ 2 }\) (6 + x) x 4
= (6 + x) × 2 = (12 + 2x) sq. cm. … (i)
Similarly Area of ∆AOB = \(\frac { 1 }{ 2 }\) (8 + x) × 4
= (16 + 2x) sq. cm … (ii)
Area of ABOC = \(\frac { 1 }{ 2 }\) (6 + 8) x 4 = 28 sq. cm … (iii)
Adding equations (i), (ii) and (iii), we have
Area of ∆ABC = [(12 + 2x) + (16 + 2x) + 28] sq.
= [56 + 4x] sq. cm … (iv)
Again perimeter of ∆ABC = AB + BC + CA = (x + 8) + (6 + 8) + (6 + x)
= (28 + 2x) cm
AB = x + 8 = 7 + 8 = 15 cm
AC = x + 6 = 7 + 6 = 13 cm.

Question 13.
Prove that opposite sides of a quadrilateral circumscribing a circle subtend supplementary angles at the centre of the circle.
Solution:
Given : A circle with centre O touches the side, PQ, QR, RS and PS of quadrilateral at the points A, B, C and D respectively.

To Prove : ∠PQQ + ∠ROS = 180°
and ∠POS + ∠QOR = 180°
Construction: Join OA, OB, OC and OD.
Proof: In ∆POD and ∆POA .
PA = FD [tangents from expemal point]
OP = OP [common]
∠ODP = ∠ODA [each 90°]
∆POD = ∆POA [RHS congruency]
∠1 = ∠2 [C.P.C.T]
Similarly we have
∠3= ∠4; ∠5 = ∠6 and ∠7 = ∠8
Now ∠1 + ∠2 + ∠3+ ∠4 + ∠5 +
∠6 + ∠7 + ∠8 = 360°
Using the above result
∠2 + ∠2 + ∠3+ ∠3+ ∠6 + ∠6 + ∠7 + ∠7 = 360°
or 2(∠2 + ∠3)+ (∠6 + ∠7)
\(\frac{360^{\circ}}{2}\) = 180°
and
∠1 + ∠1 + ∠4 + ∠4 + ∠5 + ∠5 + ∠8 + ∠8 = 360°
or 2(∠1 + ∠4 + ∠5 + ∠8) = 360°
or ∠1 + ∠4 + ∠5 + ∠8 = \(\frac{360^{\circ}}{2}\)
or (∠1 + ∠8) + (∠4 + ∠5) = 180°
or ∠POS +∠QOR = 180°

These NCERT Solutions for Class 10 Science Chapter 16 Management of Natural Resources Questions and Answers are prepared by our highly skilled subject experts to help students while preparing for their exams.

Management of Natural Resources NCERT Solutions for Class 10 Science Chapter 16

Class 10 Science Chapter 16 Management of Natural Resources InText Questions and Answers

In-text Questions (Page 269)

Question 1.
What changes can you make in your habits to become more environment friendly ?
Answer:
We have to make following changes in our habits to become more environment friendly:

• By using reusable bottles and not disposable cans.
• By keeping streets, gardens, and society clean.
• By closing taps while brushing teeth and shaving or while washing utensils.
• By using public transport. Travel in buses, trains and walking short distances.
• Stop burning garbage.
• By using material which can be recycled.
• Say ‘NO’ to plastic bags.
• Watch out for vehicle emissions.

Question 2.
What should be the advantages of exploiting resources with short terms aims ?
Answer:
Because the sources are not unlimited and with the human population increasing at a tremendous rate due to improvement in health care. The demand for all resources is increasing at an exponential rate. The management of natural resources require a long term perspective so that this will last for the generations to come and will not merely be exploited to the hilt for short term gains.

Question 3.
How would these advantages different from the advantages of using a long perspective in managing our resources?
Answer:
Initially when human population was small and level of technological development was also low, the extent to which humans could interface with the environment was limited. They lived with harmony in nature. But with the growing population, the need, have grown. Human by virtue of their mental capabilities exploited for the short term gains.

Question 4.
Why do you think there should be equitable distribution of resources? What forces would be working against an equitable distribution of our resources.
Answer:
Weather growing population, the needs of human beings have grown. Human started the exploitation of resources to meet their requirements without caring for management of resources. If there is you could table distribution of the resources among the human they will take care of the resources and utilized them carefully. So resources can be preserved for a long time, and coming generation will not be based energy crisis.

Some rich and powerful people are working against an equitable distribution of resources.

In-text Questions (Page 273)

Question 1.
Why should we conserve forest and wildlife?
Answer:
Forest or the place where diversity of plants and universities found. In other words biodiversity hotspots. As we know that all the biotic components are independent on each other as well as on the abiotic components. Loss of biodiversity or species may therefore lead to ecological instability. We will know the significance of protecting our buyer diversity. The plant and animal provide product useful to us. No life is possible without the plants. Under sources of food, fiber, timber, paper, sports equipments, medicines, oil, dies, rubber. And many other useful products such as animal, also provide us milk, meat, fiber.

So we can serve forest and Wildlife for survival of human on Earth.

Question 2.
Suggest some approaches towards the conservation of forests.
Answer:

• People recognize the need to preserve forests and wildlife, and take up the issues concerning with the government agencies
• Species are also concerned by developing network of protected areas and biosphere reserves.
• A total ban on poaching or capturing of any bird or animal. Spices should be enforced and it should be made a punishable offence.
• In essence forest resources must be used in judicious sustainable manner, which is environmentally and developmentally sound.

In-text Questions (Page 276)

Question 1.
Find out about the traditional systems of water harvesting any management in your region.
Answer:
In different region with this type of traditional systems of water harvesting are used.

• Bhundhi in MP and UP
• Kandis, Tanks, and Nadis in Rajasthan
• Band Haras and Talas in Maharastra
• Ahars and phyme sin bihar
• Kulhs I H.P
• Surangams in Kerala
• Kattas in Karnatka

Question 2.
Compare the above system with the probable system and hilly mountainous areas or planes on plateau regions.
Answer:
In hilly areas water is stored in lakes mainly. Most of the water is utilized from natural waterfalls in plain diverse and pumps tube wells and ponds are the main system of water

Question 3.
Find out this source of water in your region locality. Is water from this source available to all people living in that area?
Answer:
Rivers tube Wells, ponds wells, hand pumps, etc are the main source of water. Yes, water from this source is available to all people living in that area.

Class 10 Science Chapter 16 Management of Natural Resources Textbook Questions and Answers

Page no. 278

Question 1.
What changes would you suggest in your home in order to environment friendly?
Answer:
Everyone of us has a right to clean environment to us. Right can be fulfilled by maintaining a clean, healthy environment. The following change we have to follow at in order to be equal friendly.

• By reducing paper consumption.
• Stop burning garbage,
• Say no to plastic bags.
• By reducing consumption of water
• By reducing consumption of water. Why did using unnecessary consumption of water?
• By separating biodegradable and non-biodegradable waste is.
• Buy switch off all unnecessary appliances, electrical night.
• By adopting consume less Moto.

Question 2.
Can you suggest some changes in your school? Which would make it environment friendly?
Answer:

• There should be a established Rainwater harvesting system to raise the groundwater table.
• There should be a separate Separate. Dustbin for biodegradable. Unknown biodegradable waste.
• There should be a separate notice board to make aware to students towards environment.
• Some tips should be given by the teachers delete to the students to make them aware about environment.
• A solar panel should be established to get hot water in the campus.
• By planning of treason, increasing greenery in the school campus.

Question 3.
We saw in this chapter there are four mean stakeholders where it comes to forest and wildlife. Which among these should have their thought it to decide the management of forced? Produce. Why do you think so?
Answer:
The four stakeholders are :

• The people living in all around forests.
• The Forest Department of the government.
• The factory owners industrialists who use various forest products.
• The nature enthusiasts who want to conserve nature.

The forest department of the government ever thought you to decide the management of forest produce with the involvement of local people. Becaused local people have been working traditionally for conservation of forests. For example, Russian community in Rajasthan for whom conservation of forest and Wildlife has been a religious tenant.

Question 4.
How can you as an individual contribute or make a difference to the management of
(a) Forest and Wildlife.
(b) Water Resources.
(c) Coal Petroleum.
Answer:
(a) Forest and wildlife : Man forest relationship has been such that human dependence on forest resources for substenance was near total.

• A total ban on poaching, recapturing of any bird also animals faces should be enforced and it should be made a punishable offecse.
• Forest resources must be used in a judicious sustainable manner, which is environmentally and developmentally sound.
• Establishment of National Parks and centuries to protect biodiversity.

(b) Water Resources:

• Proper utilization of irrigation must be made. All breaches in reverse them scanners should be immediately repaired.
• Diverse should not be allowed to flirt large areas.
• Water should be supplied. To plant roots through underground pipes,
• Industrial water and domestic sewage water can be recycled and used again.
• In domestic use, wastage of water should be checked.
• Rain water harvesting is another method of conserving water.

(c) Coal and petroleum:

• We should prefer to use public transport for travelling as they consume less fuel energy per head as compared to the individual vehicles.
• We should always use efficient device appliances
• Solar cooker, solar water heater and Solar dryer should be preferred wherever possible.
• Prefer to use renewable sources of energy.

Question 5.
What can you as an individual do to reduce your consumption of the various natural resources.
Answer:

• We should close the water taps immediately after using it
• Pulses, rice etc should be soaked in water for at least 15-20 minutes before cooking.
• Consume less motto
• Keep yourself informed
• Support a conservation group.
• Save trees.
• Go on foot steps to cover approachable distances
• Plantation
• Avoid deforestation

Question 6.
List five things you have done over the last one week to:
(a) Conceive our natural resources.
(b) increase the pressure on our natural resources.
Answer:
(a) Conserve our natural resources:

• I used to go to the market by bicycle
• I closed the water taps immediately after using it
• I used public transport for travelling
• I took bath only in one bucket of water
• I reduced my paper consumption.

(b) Increase the pressure on our natural resources :

• I burnt garbage in my countryard.
• I dumped kitchen waste in a near by pond.
• I did not take care of emission of carbon dioxide from my scooter.
• I used a lot of water to wash my clothes
• I burnt coal randomly.

Question 7.
On the basis of issue raised in this chapter, what change would you incorporate in your lifestyle in a move towards a sustainable use of our resources?
Answer:

• Developing and using atternate sources of energy and minimising use of non renewable resources.
• Development of newer environment friendly technologies to prevent pollution of air, water and soil.
• Conservation of forests and wildlife by planning of trees and increasing forest area.
• Recycling of wastes and reuse of natural resources
• Harvesting of rainwater, to raise the ground water table.
• Enforcement of environmental laws.
• Say no to plastic bags
• Separate my garbage
• Stop burning garbage
• Reject disposable
• Watch out for vehicle emission
• Reduce my paper consumption
• Save water and trees
• Compost organic waste.

Class 10 Science Chapter 16 Management of Natural Resources Textbook Activities

Activity 16.1 (Page 266)

1. Find out about the international norms to regulate the emission of carbon dioxide.
2. Have a discussion in class about how we can contribute towards meeting those norms.

• By using fuels of good quality, which produce less amount of CO₂
• By plantation i.e., by growing move plants.
• By using more electric appliances.
• By using public transport in place of personal transport.
• To avoid deforestation.

Over population is not the cause of the various problems of environment. Deforestation is rapidly increasing to fulfil the demand of society. An abrupt growth of vehicles releasing a large amount of CO₂ in the environment. This problem can be reduced by following the international norms to regulate the emission of carbon- dioxide.

Activity 16.2 (Page 266)

Question 1.
There are a number of organisations that seek to spread awareness about our environment and promote activities and attitudes that lead to the conservation of our environment and natural resources. Find out about the organisation(s) active in your neighbourhood/village /town/city.
Answer:
Some organisations that seek to spread awareness about environment are :

1. Kalpavriksh, New Delhi-started a movement against the destruction of Delhi’s green areas.
2. Dasoli Gram Swarajya Mandal Gopeshwar U.P. started Chipko movement.
3. International union for conservation of Nature and Natural Resources (IUCN).
4. United Nations Environment Programme (UNEP)
5. World Wide Fund for Nature-India (WWF)

Question 2.
Find out how you can contribute towards the same cause.
Answer:
We can contribute towards the same cause as follows:

• Population stabilization
• Conservation of forests and wildlife by planting of trees and increasing forest area.
• Harvesting of rainwater, to raise the groundwater table.
• Development of new environment friendly technology to prevent pollution.
• Recyling of wastes and reuse of resources.

Activity 16.3 (Page 268)

1. Check the pH of the water supplied to your house using universal indicator or litmus paper.
2. Also check the pH of the water in the local waterbody (pond, river, lake, stream).
3. Can you say whether the water is polluted or not on the basis of your observations?

Drinking water should be colourless, odourless and tasteless. It has pH ‘6.0 – 8.5’.
House water turns blue litmus to red. It shows pH ‘6.5’.

PH 9.0 Pond
pH 8.2 River
pH 8.0 Lake
pH 6.9 stream

Activity 16.4 (Page 268)

Question 1.
Have you ever visited a town or village after a few years of absence? If so, have you noticed new roads and houses that have come up since you were there last? Where do you think the materials for making these roads and buildings have come from?
Answer:
I visited my native place after two years of absence. I saw many new roads and houses there. The material used for the construction of roads and building are arranged from brick field and hill areas.

Question 2.
Try and make a list of the materials and their probable sources.
Answer:

Question 3.
Discuss the list you have prepared with your classmates. Can you think of ways in which the use of these materials be reduced?

Activity 16.5 (Page 270)

Question 1.
Make a list of forest produce that you use.
Answer:
Table, Chair, Double bed, window, Door etc.
We all use various forest produce. But our dependency on forest resources varies. Some of us have access to alternatives, some do not. When we consider the conservation of forests, we need to look at the stakeholders who are –

• The people who live in or around forests are dependent on forest produce for various aspects of their life.
• The Forest Department of the Government which owns the land and controls the resources from forests.
• The industrialists – from those who use ‘tendu’ leaves to make bidis to the ones with paper mills – who use various forest produce, but are not dependent on the forests in any one area.
• The wildlife and nature enthusiasts who want to conserve nature in its pristine form.

Question 2.
What do you think a person living near a forest would use?

Question 3.
Discuss with your classmates how these needs differ or do not differ and the reasons for the same.

Activity 16.6 (Page 271)

Question 1.
Find out about any two forest produce that are the basis for an industry.
Answer:
Pulp (Paper Industry) Wood (Craft Industry)

Question 2.
Discuss whether this industry is sustainable in the long run or do we need to control our consumption of these products?
Answer:
Industry would consider the forest as merely a source of raw material for its factories. And huge interest groups lobby the government for access to these rew materials at articificially low rates. Since these industries have greater reach than the local people, they are not interested in the sustainability of the forest in one particular in the sustainability of the forest in one particular area. For example after cutting down all teak trees in one ares, they will get their teak from a forest farther away. They do not have any stake in ensuring that one particular area should yield on optiomal amount of some produce for all generations to come.

Activity 16.7 (Page 273)

Question 1.
Debate the damage caused to forests by the following –
(a) Building rest houses for tourists in national parks.
(b) Grazing domestic animals in national parks.
(c) Tourists throwing plastic bottles/ covers and other litter in national parks.
Answer:
(a) Building rest houses for tourists in national parks are construted on behalf of damage of trees of the forest.
(b) Grazing domestic animals in national park destroy small, leaves, flowers etc.
(c) Plastic bottles/covers and other non-biodegradable articles are harmful for the environment as well as national parks because they spread pollution.

Activity 16.8 (Page 273)

Question 1.
Villages suffering from chronic water shortage surround a water theme park in Maharashtra. Debate whether this is the optimum use of the available water.
Answer:
The earth is some times called the water-planet as this is the only plant in our solar system which has an abundant supply of water. Water is essential for all life forms. Water theme park is the proper and optimum utilisation of available water. From a water theme park villagers can understand the various ways of proper utilisation of water. This is the optimum use of the available water.

Activity 16.9 (Page 273)

Question 1.
Study the rainfall patterns in India from an atlas.
Answer:
Abundent water is found in region of Assam, West Bengal, Orissa and Coastal regions in India.

Question 2.
Identify the regions where water is abundant and the regions of water scarcity.
Answer:
Shortage of water is found in desert regions of Rajasthan, Madhya Pradesh etc.

Activity 16.10 (Page 277)

Question 1.
Coal is used in thermal power stations and petroleum products like petrol and diesel are used in means of transport like motor vehicles, ships and aeroplanes. We cannot really imagine life without a number of electrical appliances and constant use of transportation. So can you think of ways in which our consumption of coal and petroleum products be reduced?
Answer:
Some simple choices can make a difference in our energy consumption patterns. Think over the relative advantages, disadvantages and environment-friendliness of the following –

• Taking a bus, using your personal vehicle or walking/cycling.
• Using LED bulbs or fluorescent tubes in your homes.
• Using the lift or taking the stairs.
• Wearing an extra sweater or using a heating device (heater or ‘sigri’) on cold days.

The management of coal and petroleum also addresses the efficiency of our machines. Fuel is most commonly used in internal combustion engines for transportation and recent research in this field concentrates on ensuring complete combustion in these engines in order to increase efficiency and also reduce air pollution.

Activity 16.11 (Page 278)

Question 1.
You must have heard of the Euro I and Euro II norms for emission from vehicles. Find out how these norms work towards reducing air pollution.
Answer:
These norms reduce the poisonous smoke released into the air by the emission of vehicles. The vehicles will there norms emit very less smoke in the air.

Class 10 Science Chapter 16 Management of Natural Resources Additional Important Questions and Answers

Very Short Answer Type Questions

Question 1.
What is preservatives?
Answer:
It refers to no use of resources.

Question 2.
What is sustainable development?
Answer:
Development which meets the needs of the present generation as well of future generations.

Question 3.
What is chippo movement?
Answer:
A movement started in Gharwal in the Himalayas to stop cutting the trees.

Question 4.
What are natural resources?
Answer:
Coal, petroleum, forests, water etc.

Question 5.
What is Coliform?
Answer:
It is a group of bacteria found in human intestine

Short Answer Type Questions

Question 1.
What do you mean by reduce. Give some examples.
Answer:
Reduce mean that you use less.
For example

• Buy only what you need
• Use both sides of paper
• Save water by repairing taps.
• Take only that much food that you can consume
• Save electricity by switching of unnecessary lights and fans.

Question 2.
What do you mean by recycle?
Answer:
Recycle means that you use less
For example

• Buy only that you need
• Use both sides of paper
• Save water by repairing leaking taps
• Take only that much food that you can consume
• Save electricity by switching off necessary lights and fan.

Question 3.
What do you mean by recycle ?
Answer:
Recycle means using the resources same again and again but in modified form, e.g.,

• Old newspaper can be recycled to make tissue paper and cardboard.
• Organic waste can be allowed to rot and manure can be prepared.
• Recycle glass, plastics aluminium cans other metals to produce useful products.

Question 4.
What do you mean by reuse? Give some examples
Answer:
It means using the same resources again in the same form, such as refilling cold drinks bottle.
For example

• reuse plastic items like bags bottle cups, etc.
• reuse empty glass bottles as container for storing things.
• reuse Cloth jute or paper bags Instead. Of using new plastic bags.

Long Answer Type Questions

Question 1.
In order to obtain sustainable development word changes would you like to incorporate ?
or
Give some practices for sustainable development and conserving the environment.
Answer:
Practices for sustainable development and consuming the environment are:

• Population stabilization.
• Social and cultural changes.
• Developing and using alternate source of energy and minimizing use of non-renewable resources.
• Enforcement of environmental laws.
• Establishment of national parks and centuries to protect biodiversity
• Harvesting the groundwater to raise the groundwater table.
• Use of biomass for producing products of industrial and commercial importance.
• Recycling of wastes and reuse of resources.
• Phones. Conservation of forests and Wildlife by planting of trees and increasing forest area.
• Development of newer environment friendly techniques and prevent pollution of air, water and soil.

Multiple Choice Questions

Question 1.
Bishnoi is an eco-religion is started by:
(a) Guru Jamesburg
(b) Guru Golwalker Ji
(c) Sundar Lai Bahugana
(d) Amrita Devi
Answer:
(a) Guru Jamesburg

Question 2.
Coliform is a class of
(a) Virus
(b) Bacteria
(c) Fungi
(d) Tree
Answer:
(b) Bacteria

Question 3.
3R’s means?
(a) Reduce
(b) Reuse.
(c) Recycle
(d) All of the above
Answer:
(d) All of the above

Question 4.
Reuse means using the same resources again in the.
(a) same form.
(b) Modified form.
(c) Less form.
(d) All of the above.
Answer:
(a) same form.

Question 5.
Recycle means using the same resources again in the
(a) same form.
(b) Modified form.
(c) Less form.
(d) All of the above.
Answer:
(b) Modified form.

These NCERT Solutions for Class 10 Science Chapter 15 Our Environment Questions and Answers are prepared by our highly skilled subject experts to help students while preparing for their exams.

Our Environment NCERT Solutions for Class 10 Science Chapter 15

Class 10 Science Chapter 15 Our Environment InText Questions and Answers

In-text Questions (Page 257)

Question 1.
Why are some substances biodegradable and some non-biodegradable?
Answer:
Some substances are biodegradable because the enzymes released by the micro-organism helps in breaking down the biodegradable wastes but some are non-biodegradable because they can not be broken down by the micro-organism.

Question 2.
Give any two ways in which biodegradable substances would affect the environment.
Answer:

1. Biodegradable substances like food materials rancid after some time and produce bad smell and causes air pollution.
2. Biodegradable substances causes water pollution and make it unfit for domestic purposes.

Question 3.
Give any two ways in which non-biodegradable substances would affect the environment.
Answer:

1. Non-biodegradable substances concentrated at different trophic levels and causes various health problems in human beings and animals.
2. Non-biodegradable substances do not break-down by organisms in the simpler substances so they disturb terrestrial and aquatic ecosystems.

In-text Questions (Page 261)

Question 1.
What are the trophic levels? Give an example of a food chain and state the different trophic level.
Answer:
The various links or steps representing organisms in a food chain at which the transfer of food and energy takes place are called trophic levels.

For example in the following food chain.
Plants → Deer → Lion

The plants constitute the first trophic level. Deer constitute the second trophic level and Lion constitute the third trophic level. Plants produce their food themselves in presence of sun light so they constitute first trophic level. Deer consume plants so it. constitute second trophic level. Lion consume deer so it constitute third trophic level.

Question 2.
What is the role of decomposers in the ecosystem?
Answer:
Decomposers consume, and thus decompose, the dead Demains of the other organisms i.e, autotrophs and heterotrophs. For example, certain bacteria and fungi break down the complex compounds present in the dead organisms into simpler-substances. Through the decomposers the elements enter the earth again, which are in turn again taken up by the plants. So, the cycle of exchange of matter continues. By their activity, the decomposers also maintain soil fertility.

In-text Questions (Page 264)

Question 1.
What is ozone and how does it affect any ecosystem?
Answer:
Ozone (O₂) is a molecular gas formed by three atoms of oxygen. While O₂, which we normally refer to as oxygen, is essential for all aerobic forms of life, ozone is a deadly poison. However at the higher levels of the atmosphere, ozone performs an essential functions, it shields the surface of the earth from ultraviolet radiation from the sun. This radiation is highly damaging to organisms, for example, it is known to cause skin cancer in human beings.

Is stratosphere ozone form a layer, known as ozone layer which protect us from harmful ‘UV’ rays of Sun. But due to some holes in the ozone layer ‘UV’ rays are reaching on earth and increasing its temperature. The increase in temperature of earth is causing global warming. So ozone can affect all ecosystems on earth.

Question 2.
How can you help in reducing the problem of waste disposal? Give any two methods.
Answer:
With the growing population, the generation of wastes is increasing day by day. Increased use of disposable items is also in favour of increasing waste. The problem of waste disposal can be reduced as follows :

• By using disposable paper cups.
• By using disposable cups made of clay or by using steel.

Class 10 Science Chapter 15 Our Environment Textbook Questions and Answers

Page no. 264

Question 1.
Which of the following groups contains only biodegrable items ?
(a) Grass, flower, leather
(b) Grass, wood and plastic
(c) Fruit-peels, cake and lime-juice
(d) Cake, wood and grass
Answer:
(d) Cake, wood and grass.

Question 2.
Which of the following constitute a food- chain?
(a) Grass, wheat and mango
(b) Grass, goat and human
(c) Goat, cow and elephant
(d) Grass, fish and goat
Answer:
(b) Grass, goat and human

Question 3.
Which of the following are environment-friendly practices?
(a) Carrying cloth bags to put purchases in while shopping
(b) Switching off unnecessary lights and fans
(c) Walking to school instead of getting your mother to drop you on her scooter
(d) All of the above
Answer:
(d) All of the above

Question 4.
What will happen if we kill all the organisms in one trophic level?
Answer:
The various lins or steps representing organisms in a food chain at which the transfer of food and energy takes place are called trophic’ levels. For examples, plants constitute the first trophic level and the herbivores consumer plants e.g, deer or cow they constitute second trophic level. Lion consume deer, so lion consitute third trophic lelve. If we kill all the organisms of the one trophic level then food or energy cannot be transferred to the next trophic level and the organisms of this trophic level and all organisms of next to this trophic level will suffer for survival.

Question 5.
Will the impact of removing all the organisms in a trophic level be different for different trophic levels? Can the organisms of any trophic level be removed without causing any damage to the ecosystem?
Answer:
Yes the impact of removing all the organisms in a trophic level will be different for different trophic level. For example, let all the organisms of third trophic level has been removed, so the number of organisms of second trophic level will be increased with a great number and they will consume large quantity of first trophic level so the quantity of first trophic level decreases sharply. No the removal of organisms of any trophic level causes damage to the ecosystem.

Question 6.
What is biological magnification? Will the levels of this magnification be different at different levels of the ecosystem?
Answer:
Unknowingly some harmful chemical enter our body through the food chain such as pesticides, weedicides and rodenticides etc. These chemicals are either washed down into the soil and finally enter the water or are taken up from the soil by the plants along with water and minerals and thus enter the food chain. As these chemicals are not degradable, these harmful chemicals get concentrated at each trophic level. This is known as biomagnification or biological magnification.

The levels of the magnification will be different at different trophic levels of the ecosystem. The animals at the highest trophic level or the extreme right side of the food chain have the maximum concentration of harmful chemicals in the body.

Question 7.
What are the problems caused by the non-biodegradable wastes that we generate?
Answer:
The waste materials which cannot be broken down to non-poisonous substances easily are called non-biodegradable wastes. Bacteria and other saprophytes cannot break down such wastes. For example, DDT, plastics, polythene bags, synthetic fibre, glass, aluminium cans, iron nails and radioactive (nuclear) wastes.

Non-biodegradable waste cause the following problems :
1. Poisonous chemicals like DDT and other pesticides remain as such in the biosphere for a long time. These enter the food chain where they get biomagnified at each trophic level.

2. Industrial or mining wastes are toxic and cumulative in their harmful effects. Accumulation of metals contain by industrial wastes in a human body can cause permanent damage to the human systems.

3. Polychlorinated biphenyls are resistant to oxidation and highly stable. These are used in transformers and capacitors. Release of PCBs in the air causes skin disorders. They are reported to be carcinogenic.

4. Nuclear radiations causes somatic effects ie, it lead to deadly diseases like cancer and genetic disorders.

Question 8.
If all the waste we generate is biodegradable will this have no impact on the environment?
Answer:
Waste that can be broken down to non-poisonous or harmful substances by the action of certain micro-organism are called biodegradable wastes. The enzymes released by microorganisms helps in breaking down the biodegradable wastes.

Waste in any form i.e., biodegradable or non-biodegradable have an impact on the environment. So we cannot say that if all the waste is biodegradable it will not have any impact on the environment.

Question 9.
Why is damage to the ozone layer a cause for concern? What steps are being taken to limit this damage?
Answer:
The most important gas present in the stratosphere is ozone. At an altitude of about 23 km, its concentration is about 10 ppm.

Ozone absorbs ultraviolet radiation coming from the sun and thus protect us from the harmful effects of the ultraviolet radiation, Ultraviolet rays are known to cause skin cancer, eye damage and damage to the immune system. It also kills the minute aquatic plant life, the phytoplanton. But the amount of ozone in the atmosphere began to drop sharply in 1980s. This decrease has been linked to synthetic chemicals like CFCs which are used as refrigerants and is fire extinguishers. Ozone is a very reactive compelem and it oxidise CFCs. In doing so, ozone is converted into gain oxygen.

Ozone + CFG → Oxygen + Oxidation

Thus ozone layer is depleled and it allows the harmful radiations i.e., ‘UV’ radiations on earth which cause so many negative effect on human beings, which are already discussed. So depletion of ozone layer is harmful for living things on earth.

Control Measures:

1. By reducing the use of CFCs, many countries have already banned the use of CFCs.
2. By developing substitutes to replace CFCs. These include the compounds called hydro-fluoro-carbons (HFC-134), hydro-chlorofluro-carbons (HCFCs) and methycyclohexane (MCH).

Class 10 Science Chapter 15 Our Environment Textbook Activities

Activity 15.1 (Page 256)

• Collect waste material from your homes. This could include all the waste generated during a day, like kitchen waste (spoilt food, vegetable peels, used tea leaves, milk packets and empty cartons), waste paper, empty medicine bottles/strips/bubble packs, old and torn clothes and broken footwear.
• Bury this material in a pit in the school garden or if there is no space available, you can collect the material in an old bucket/ flower pot and cover with at least 15 cm of soil.
• Keep this material moist and observe at 15-day intervals.

Question 1.
What are the materials that remain unchanged over long periods of time?
Answer:
The materials that remain unchanged over long periods of time are: Milk packets, empty medicine bottles, broken footwear.

Question 2.
What are the materials which change their form and structure over time?
Answer:
The materials which change their form and structure over time are : spoilt food, vegetable peels, used tea leaves, empty cartoons, waste paper, strips, bubble packs, old and tom clothes.

Question 3.
Of these materials that are changed, which ones change the fastest?
Answer:
Spoilt food changed the fastest.

Activity 15.2 (Page 257)

Question 1.
Use the library or internet to find out more about biodegradable and non-biodegradable substances.
Answer:
The substances that are broken down by biological processes are called biodegradable, e.g. food, paper, wood etc.
The substances that are not broken down by biological processes are called non-biodegradable, e.g plastics, rubber etc.

Question 2.
How long are various non-biodegradable substances expected to last in our environment?
Answer:
The non-biodegradable substances may be inert and simply persist in the environment for a long time.

Question 3.
These days, new types of plastics which are said to be biodegradable are available. Find out more about such materials and whether they do or do not harm the environment.
Answer:
Now a days a number of new types of plastics are available. These plastics are biodegradable and do not harm the environment.

Activity 15.3 (Page 258)

• You might have seen an aquarium. Let us try to design one.
• What are the things that we need to keep in mind when we create an aquarium? The fish would need a free space for swimming (it could be a large jar), water, oxygen and food.
• We can provide oxygen through an oxygen pump (aerator) and fish food which is available in the market.
• If we add a few aquatic plants and animals it can become a selfsustaining system. Can you think how this happens? An aquarium is an example of a human-made ecosystem.
• Can we leave the aquarium as such after we set it up? Why does it have to be cleaned once in a while? Do we have to clean ponds or lakes in the same manner? Why or why not?

Observation : If we add a few aquatic plants and animals in an aquarium it can be a self sustaining system if animals are able to take food directly from plants otherwise it will not be a sell sustaining system. No we cannot leave the aquarium as such after we set it up An aquarium should be cleaned once in a while because refuse or debris of fish collected in the aquarium can pollute the water of the aquarium. No, we do not have to clean ponds or lakes in the same manner because these cover a large area and many organisms living in it can die.

Activity 15.4 (Page 259)

Question 1.
While creating an aquarium did you take care not to put an aquatic animal which would eat others? What would have happened otherwise?
Answer:
While creating an aquarium we should take care not to put an aquatic animal which would eat other because after consuming all animals, carnivores face food crisis and lastly they will die.

Question 2.
Make groups and discuss how each of the above groups of organisms are dependent on each other.
Answer:
We know that organisms can be grouped as producers, consumers and decomposers according to the manner in which they obtain their sustenance from the environment.

Question 3.
Write the aquatic organisms in order of who eats whom and form a chain of at least three steps.

Answer:
Phytoplanktons → Zooplanktons → Small fish.

Question 4.
Would you consider any one group of organisms to be of primary importance? Why or why not?
Answer:
In aquatic system phytoplanktons (algae) are basically needed because they are producers.

Activity 15.5 (Page 261)

1. Newspaper reports about pesticide levels in ready-made food items are often seen these days and some states have banned these products. Debate in groups the need for such bans.
2. What do you think would be the source of pesticides in these food items? Could pesticides get into our bodies from this source through other food products too?
3. Discuss what methods could be applied to reduce our intake of pesticides.

• The chemical substances that are used to kill, or block the reproductive process in harmful organisms such as rodents, insects, mites, bacteria, fungi etc. are called pesticides.
• There is an international standard for the use of pesticides in food items to protect them from bacteria, fungi etc. But in India the quantity of pesticides added in food items is more than hundred times as compared to international standard. That is why some states banned these products. Pesticides are highly harmful for health so a ban is justified on ready-made food items containing a high level of the pesticides.
• Basically the pesticides are added in food items to protect from bacteria and fungi during their preparation. In our bodies pesticides can enter through food chain. As these chemicals are not degradable, these get accumulated progressively at each trophic level. As human beings occupy the top level in any food chain, the maximum concentration get accumulated in our bodies.
• An International standard should be followed for the”use of pesticides in food items.
• Natural methods should be preferred to get a good crop.
• Minimum use of pesticides.
• All the vegetables, fruits etc. should be washed with water properly before use. Pulses, rice, grams, etc. should be kept in water for 10-11 minutes and washed 3-4 times with water before cooking,
• Avoid the use of ready-made food items, cold drinks burger etc.

Activity 15.6 (Page 262)

Question 1.
Find out from the library, internet or newspaper reports, which chemicals are responsible for the depletion of the ozone layer.
Answer:
Mainly chlorofluorocarbons (CFCs) ie the compounds of carbon, chlorine and fluorine and ‘NO’ are responsible for the depletion of the ozone layer.

Question 2.
Find out if the regulations put in place to control the emission of these chemicals have succeeded in reducing the damage to the ozone layer. Has the size of the hole in the ozone layer changed in recent years?
Answer:
The United Nations Environment Programme succeeded in forging an agreement to freeze CFC production at 1986 level. Yes these regulations put in place to control the emission of CFCs and other chemicals have succeeded in reducing the damage to the ozone layer. Yes the size of the ozone layer has changed in the recent years.

Activity 15.7 (Page 262)

Question 1.
Find out what happens to the waste generated at home. Is there a system in place to collect this waste?
Answer:
Two waste generated at home is collected in a dustbin. It is good if the biodegradable and non-biodegradable waste collect separately. So it can be disposed easily.

Question 2.
Find out how the local body (panchayat, municipal corporation, resident welfare association) deals with the waste. Are there mechanisms in place to treat the biodegradable and non-biodegradable wastes separately?
Answer:
Generally local body does not treat the bioderadable and non-biodegradable waste separately. Now-a-days in some towns and cities waste material treatment plants are established in which the biodegradable and non-biodegradable wastes are treated separately.

Activity 15.8 (Page 263)

Question 1.
Calculate how much waste is generated at home in a day.
Answer:
In a common family of ‘3-4’ members approximately 2 to 3 kg wastes generated in a day.

Question 2.
How much of this waste is biodegradable?
Answer:
Approximately 70% of this waste is biodegradable.

Question 3.
Calculate how much waste is generated in the classroom in a day.
Answer:
Approximately 1 to 2 kg wastes is generated in the classroom in a day.

Question 4.
How much of this waste is biodegradable?
Answer:
Approximately 80% of this waste is biodegradable.

Question 5.
Suggest ways of dealing with this waste.
Answer:
Bio-degradable wastes generally papers should be burnt in a separate comer of the school and non-biodegradable wastes should be sold so that it can be recycled again like polythene, glass bottles etc.

Activity 15.9 (Page 263)

Question 1.
Find out how the sewage in your locality is treated. Are there mechanisms in place to ensure that local water bodies are not polluted by untreated sewage.
Answer:
The city sewage is the main source of pollution in rivers and takes etc. In our locality it is treated as follows.
The large floating and suspended matter, grit, oil and grease are removed by filtration through screens. The wastewater flows through a channel and the solids retained by the screens are disposed of into the land fields. So to keep our water bodies such as rivers, lakes and nearby seashores clean, the sewage waste must be properly treated before discharging into any water body. So this mechanism ensures that the soil and water are not polluted by untreated sewage.

Question 2.
Find out how the local industries in your locality treat their wastes. Are there mechanisms in place to ensure that the soil and water are not polluted by this waste?
Answer:
In our locality, industries treat wastes as follows:
Basically the treatment of wasles depend on its nature. By recycling process a number of waste material can be treated in different industries such as glass industry, Iron and steel industry etc.

Commonly industries leave water treatment plant to purify waste water and then dump this water into canal or rivers.

Activity 15.10 (Page 263)

Question 1.
Search the internet or library to find out what hazardous materials have to be dealt with while disposing of electronic items. How would these materials affect the environment?
Answer:
Electronic items include T.V. Refrigerators, VCD, VCR, Cooler, A.C., Computer. While disposing electronic items hazardous materials such as glass, plastics etc. should be dealt from the electronic items. Thes materials are non-biodegradable so they pollute soil, water etc.

Question 2.
Find out how plastics are recycled. Does the recycling process have any impact on the environment?
Answer:
When waste plastic material is heated at a high temperature it is melted and can be moulded in desired shape again. Recycling process has a very little impact on the environment because during recycling some vapours are formed which pollute air.

Class 10 Science Chapter 15 Our Environment Additional Important Questions and Answers

Very Short Answer Type Questions

Question 1.
What are the components of environment?
Answer:

• Atmosphere
• Hydrosphere
• Lithosphere
• Biosphere.

Question 2.
Which is the largest Biological system on earth?
Answer:
Biosphere

Question 3.
What is the smallest functional unit of Biosphere?
Answer:
Ecosystem

Question 4.
What is an ecosystem?
Answer:
The functional unit of environment in which living organisms interact with one another as well as with the non-living components.

Question 5.
Give an example of a real natural ecosystem.
Answer:
A pond ecosystem.

Short Answer Type Questions

Question 1.
Explain decomposers or saprophytes with examples.
Answer:
Saprophytes consume both autotrophs and heterotrophs and thus decompose, the dead remains. For example, certain bacteria and fungi break down the complex organic compounds present in the dead organisms into simpler substances. Through the decomposers the elements enter the earth again, which are in turn again taken up by the plants. Thus, the cycle of exchange of matter continues. Decomposers also maintain soil fertility.

Question 2.
How is ozone formed? Give chemical equations.
Answer:
Ozone is formed in the stratosphere. When UV rays falls on oxygen molecules (O₂), as a result molecule of oxygen is split into nascent oxygen atoms. These oxygen atoms then combine with the molecular oxygen to form ozone.

Question 3.
What are the causes of Ozone depletion?
Answer:
There are several reasons for the depletion of Ozone layer. The chloroflurocarbons are mainly responsible for depletion of Ozone layer and the other factor is nitrogen monoxide (NO). CFCs are gases which readily solidify when compressed. This makes them useful in refrigeration as propellants in fire extinguishers, in aerosol cans and in plastic foams. CFCs are very stable compounds and accumulate in the upper atmosphere, where they react with ozone. Ozone is a very reactive element and it oxidizes CFCs. In doing so, Ozone is converted into Oxygen.

Ozone + CFC → Oxygen + Oxidation Products.

Nitrogen monoxide (NO) is released in the upper atmosphere from the exhausts of high altitude aircraft. Ozone oxidises nitrogen monoxide to nitrogen dioxide (NO).
Ozone + NO – Oxygen + NO₂

Long Answer Type Question

Question 1.
What are the features of an ecosystem?
Answer:
The features of an ecosystem are :

• An ecosystems is a self-sustaining, structural and functional unit of biosphere in which living organisms interact with each other as well as with the abiotic components like air, water and soil.
• It depends on solar energy which is captured by the green plants and passed on to the subsequent heterotrophic organisms Without assures of energy, an ecosystem will not be able to function.
• An ecosystem is an open system in terms of energy and a closed system as flow of minerals is concerned.
• A pond, a lake, a river, a forest, a desert even a man-made aquarium and a crop field are all examples of ecosystems.

Multiple Choice Questions

Question 1.
The flow of energy in a food chain is
(a) unidirectional
(b) Two-directional
(c) Three-directional
(d) Multi-directional
Answer:
(a) unidirectional

Question 2.
The sequential process of eating and being eaten is called
(a) Food web
(b) Food chain
(c) Energy flow
(d) Trophic level
Answer:
(b) Food chain

Question 3.
Man is a
(a) Producer
(b) Carnivore
(c) Herbivore
(d) Omnivore
Answer:
(d) Omnivore

Question 4.
Municipal solid waste, commonly called
(a) Domestic waste
(b) biodegradable waste
(c) garbage
(d) Sewage
Answer:
(c) garbage

Question 5.
Non-biodegradable wastes is/are
(a) Paper
(b) Human excreta
(c) DDT, BHC
(d) Vegetables, Plastic
Answer:
(c) DDT, BHC