Question

A hemispherical bowl is made of steel 0.25 cm thick. The inner radius of the bowl is 5 cm. Find the outer curved surface area of the bowl.
A. 173$c{m^2}$
B. 133$c{m^2}$
C. 143$c{m^2}$
D. 273$c{m^2}$

Answer 1

Hint: In this particular type of question we have to proceed by first finding the outer radius of the hemispherical bowl. Then we have to use the formula for Curved Surface Area (CSA) of the hemispherical bowl to get to the desired answer.

Complete step-by-step answer:

Given:
The thickness of bowl is 0.25cm and the inner radius = 5cm ,
From figure: Outer radius = inner radius + thickness
$ \Rightarrow {\text{Outer radius = 5cm + 0}}{\text{.25cm = 5}}{\text{.25 cm}}$
We know that Outer Curved Surface Area of the bowl ( hemisphere ) = $2\pi \times radiu{s^2}$
$ = 2 \times \dfrac{{22}}{7} \times {5.25^2} = 2 \times \dfrac{{22}}{7} \times 5.25 \times 5.25 = 173.25c{m^2} \approx 173c{m^2}$

Note: It is important to understand the concept used in solving such types of questions. The formula for CSA of the hemisphere should be recalled. Note that the Curved Surface Area of the hemisphere is the area without the circular bottom, hence it is open from one side. The total area of the hemisphere consists of outer , inner area and the area of the circular bottom which was not required in this particular type of question.