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Surface Area of a Sphere

Surface area of a sphere_1The surface area of a sphere with radius r is obtained by multiplying 4, pi and radius squared.

The formula for surface area of a sphere is :

Surface Area (SA)  =  4pir2

or  SA  =  4 x pi x (radius)2

 

Example 1 : What is the surface area of a sphere with radius 15 cm?

SA  =  4pir2

=  4 x 3.14 x 152

=  2827.4 cm2 (correct to 1 decimal place)

 

Example 2 : What is the surface area of a sphere with diameter 22 cm?

SA  =  4pir2

=  4 x 3.14 x 112   (r = 22/2 = 11 cm)

=  1519.8 cm2 (correct to 1 decimal place)

 

Surface Area of a Hemisphere

Surface area of a sphere_2A hemisphere is half of a sphere, and the surface area of a hemisphere is half the surface area of a sphere.

So the formula for surface area of a hemisphere is:

Surface Area (SA)  =  2pir2

or  SA  =  2 x pi x (radius)2

 

Example 3 : What is the surface area of a hemisphere with radius 12 cm?

SA  =  2pir2

=  2 x 3.14 x 122

=  904.3 cm2 (to 1 decimal place)

 

Example 4 : What is the surface area of a hemisphere with diameter 36 mm?

SA  =  2pir2

=  2 x 3.14 x 182 (since r = 18 mm)

=  2034.7 mm2 (to 1 decimal place)