NCERT Class 9 Solutions: Surface Areas and Volumes (Chapter 13) Exercise 13.4 – Part 1

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Q-1 . Find the surface area of a sphere of radius:

  1. 10.5cm

  2. 5.6cm

  3. 14cm

Solution:

Formula for calculating the surface area of sphere.

Surface Area of a Sphere

Formula for calculating the surface area of sphere.

  1. Radius of the sphere (r) =10.5cm

    • 4πr2

    • (4×227×10.5×10.5)cm2

    • 1386cm2

  2. Radius of the sphere (r) =5.6cm

    Surface area

    • 4πr2

    • (4×227×5.6×5.6)cm2

    • 394.24cm2

  3. Radius of the sphere (r) =14cm

    Surface area

  • 4πr2

  • (4×227×14×14)cm2

  • 2464cm2

Q-2 Find the surface area of a sphere of diameter:

  1. 14cm

  2. 21cm

  3. 3.5m

Solution:

  1. r=142cm=7cm ( radius=diameter2 )

    Surface area

    • 4πr2

    • (4×227×7×7)cm2

    • 616cm2

  2. r=212cm=10.5cm ( radius=diameter2 )

    • 4πr2

    • (4×227×10.5×10.5)cm2

    • 1386cm 2

  3. r=3.52m=1.75m ( radius=diameter2 )

  • 4πr2

  • (4×227×1.75×1.75)m2

  • 38.5m2

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