Question:
Find the surface area of a sphere of diameter:
(i) 14 cm
(ii) 21 cm
(iii) 3.5 cm
Solution:
(i) Given Diameter = 14 cm
Radius = Diameter/2
= 14/2 = 7 cm
Surface area $=4 \pi r^{2}$
$=4 \times 22 / 7 \times(7)^{2}$
$=616 \mathrm{~cm}^{2}$
(ii) Given Diameter = 21cm
Radius = Diameter/2
= 21/2 = 10.5 cm
Surface area $=4 \pi r^{2}$
$=4 \times 22 / 7 \times(10.5)^{2}$
$=1386 \mathrm{~cm}^{2}$
(iii) Given diameter = 3.5 cm
Radius = Diameter/2
= 3.5/2 = 1.75 cm
Surface area $=4 \pi r^{2}$
$=4 \times 22 / 7 \times(1.75)^{2}$
$=38.5 \mathrm{~cm}^{2}$