Surface Areas & Volumes | Exercise 13.4 | Q1

Question 1: Find the surface area of a sphere of radius:
(i) 10.5 cm
(ii) 5.6 cm
(iii) 14 cm

Explanatory Answer | Exrecise 13.4 Question 1

Part (i): Radius of the sphere, r = 10.5 cm

Surface area of sphere = 4 × π × r²
Take π = \\frac{22}{7})
Surface area of sphere = 4 × \\frac{22}{7}) × 10.5 × 10.5
= 4 × 22 × 1.5 × 10.5
= 1386 cm²

Part (ii): Radius of the sphere, r = 5.6 cm

Surface area of sphere, r = 4 x π × r²
Take π = \\frac{22}{7})
Surface area of sphere = 4 × \\frac{22}{7}) × 5.6 × 5.6
= 4 × 22 × 0.8 × 5.6
= 394.24 cm²

Part (iii): Radius of the sphere, r = 14 cm

Surface area of sphere = 4 × π × r²
Take π = \\frac{22}{7})
Surface area of sphere = 4 × \\frac{22}{7}) × 14 × 14
= 4 × 22 × 2 × 14
= 2464 cm²

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 ▶