Question

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

Answer 1

(i) Diameter of a sphere = 14 cm
$\therefore Radius\left(r\right)=\frac{14}{2}=7cm\therefore Surfacearea=4\pi r^2=4\times \frac{22}{7}\times 7\times 7=616c{m}^2$
(ii) Diameter of the sphere = 21 cm
$\therefore Radius\left(r\right)=\frac{21}{2}cm\therefore Surfacearea=4\pi r^2=4\times \frac{22}{7}\times \frac{21}{2}\times \frac{21}{2}c{m}^2=1386c{m}^2$
(iii) Diameter of the sphere = 3.5 cm

$\therefore Radius\left(r\right)=\frac{3.5}{2}=\frac{7}{2\times 2}=\frac{7}{4}cm$
$\therefore Surfacearea=4\pi r^2$
$=4\times \frac{22}{7}\times \frac{7}{4}\times \frac{7}{4}c{m}^2$
$=\frac{77}{2}=38.5c{m}^2$