# NCERT Solutions For Class 9 Math | Exercise 13.4

###### Chapter 13: Surface Areas & Volumes | Surface Area of Sphere | Hemisphere

Exercise 13.4 of class 9 NCERT math text books comprises 9 questions. This exercise focuses on curved surface area of sphere, curved surface area of hemisphere and total surface area of hemisphere.

#### How to find the Surface Area of Sphere? What is the formula for Surface Area of Sphere?

The formula to compute the curved surface area of sphere is 4πr2, where 'r' is the radius of the sphere.

#### What is the formula for Curved Surface Area of Hemisphere? What is the formula for Total Surface Area of Hemisphere?

The formula to compute the curved surface area of hemisphere (CSA of hemisphere) is 2πr2, where 'r' is the radius of the hemisphere.

The formula to compute the total surface area of hemisphere (TSA of hemisphere) is 3πr2, where 'r' is the radius of the hemisphere.

The total surface area of hemisphere is the sum of the curved surface area of hemisphere and the area of the circular base of the hemisphere.

1. Question 1

Find the surface area of a sphere of radius:
(i) 10.5 cm
(ii) 5.6 cm
(iii) 14 cm

2. Question 2

Find the surface area of a sphere of diameter:
(i) 14 cm
(ii) 21 cm
(iii) 3.5m

3. Question 3

Find the total surface area of a hemisphere of radius 10 cm. (Use π = 3.14)

4. Question 4

The radius of a spherical balloon increases from 7 cm to 14 cm as air is being pumped into it. Find the ratio of surface areas of the balloon in the two cases.

5. Question 5

A hemispherical bowl made of brass has inner diameter 10.5 cm. Find the cost of tin-plating it on the inside at the rate of Rs.16 per 100 cm2.

6. Question 6

Find the radius of a sphere whose surface area is 154 cm2.

7. Question 7

The diameter of the moon is approximately one fourth of the diameter of the earth. Find the ratio of their surface areas.

8. Question 8

A hemispherical bowl is made of steel, 0.25 cm thick. The inner radius of the bowl is 5 cm. Find the outer curved surface area of the bowl.

9. Question 9

A right circular cylinder just encloses a sphere of radius r. Find
(i) surface area of the sphere
(ii) curved surface area of the cylinder,
(iii) ratio of the areas obtained in (i) and (ii)

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