Question

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

Answer 1

(i) Diameter, d = 14 cm
Radius, r = \(\frac{14cm}{2}\) = 7cm

Surface area of a sphere = \(4\pi r^2\)
= 4 × \(\frac{22}{7}\) × 7cm × 7cm
= 616 cm²

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(ii) Diameter, d = 21 cm
Radius, r = \(\frac{21cm}{2}\)

Surface area of a sphere = \(4\pi r^2\)
\(= \frac{4}{2} × \frac{22}{7} × \frac{21}{2} × \frac{21}{2}\)
= 1386 cm²

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(iii) Diameter, d = 3.5 m
Radius, r =\( \frac{3.5}{2}\) = 1.75m

Surface area of a sphere = \(4\pi r^2\)
= 4 × \(\frac{22}{7} \)× 1.75m x 1.75m
= 38.5 m²

The surface area of a sphere with diameters 14 cm, 21 cm, and 3.5 m are 616 cm², 1386 cm², and 38.5 m² respectively.