Surface Areas & Volumes | Exercise 13.4 | Q2

Question 2: Find the surface area of a sphere of diameter:

(i) 14 cm
(ii) 21 cm
(iii) 3.5m

Explanatory Answer | Exrecise 13.4 Question 2

Part (i): Diameter of the sphere, d = 14 cm

Radius of the sphere, r = \\frac{d}{2}) = \\frac{14}{2}) = 7 cm
Surface area of sphere = 4 × π × r²
Take π = \\frac{22}{7})
Surface area of sphere = 4 × \\frac{22}{7}) × 7 × 7
= 4 × 22 × 7
= 616 cm²

Part (ii): Diameter of the sphere, d = 21 cm

Radius of the sphere, r = \\frac{d}{2}) = \\frac{21}{2}) cm
Surface area of sphere = 4 × π × r²
Take π = \\frac{22}{7})
Surface area of sphere = 4 × \\frac{22}{7}) × \\frac{21}{2}) × \\frac{21}{2})
= 22 × 3 × 21
= 1386 cm²

Part (iii): Diameter of the sphere, d = 3.5 m

Radius of the sphere, r = \\frac{d}{2}) = \\frac{3.5}{2}) m
Surface area of sphere = 4 × π × r²
Take π = \\frac{22}{7})
Surface area of the sphere = 4 × \\frac{22}{7}) × \\frac{3.5}{2}) × \\frac{3.5}{2})
= 22 × 0.5 × 3.5
= 38.5 m²

Exercise 13.1 | Surface Area of Cubes & Cuboids

1. Class 9 Exercise 13.1 Question 3 | Height of hall ▶
2. Class 9 Exercise 13.1 Question 6 | TSA of Herbarium ▶
3. Class 9 Exercise 13.1 Question 7 | Shanti Sweets ▶

Exercise 13.2 | Surface Area of Cylinders

1. Class 9 Exercise 13.2 Question 3 | CSA TSA of Metal Pipe ▶
2. Class 9 Exercise 13.2 Question 4 | Roller & Playground ▶
3. Class 9 Exercise 13.2 Question 9 | Cylindrical Petrol Tank ▶
4. Class 9 Exercise 13.2 Question 10 | CSA of Decorative Lampshade ▶

Exercise 13.3 | Surface Area of Cones

1. Class 9 Exercise 13.3 Question 5 | Length of Tarpaulin 3 m wide ▶
2. Class 9 Exercise 13.3 Question 8 | Cost of painting conical barricades ▶

Exercise 13.4 | Surface Area of Spheres & Hemispheres

1. Class 9 Exercise 13.4 Question 8 | Outer CSA of hemispherical bowl ▶
2. Class 9 Exercise 13.4 Question 9 | Surface area of sphere & Cylinder ▶