Question

Find the surface area of a sphere with a diameter of:

(ii) $\mathbf{21}\mathbf{}\mathbf{cm}$

Answer 1

Calculate the surface area of sphere.

As we know that,

Surface area of sphere$=4\mathrm{\pi }{r}^2$

Where $r$ is radius of sphere and $\mathrm{\pi }=\frac{22}{7}$

Given that, diameter $d=21\mathrm{cm}$

So that, radius $r=\frac{21}{2}=10.5\mathrm{cm}$

$$\begin{gathered} \therefore \mathrm{Surface}\mathrm{area}=4\times \frac{22}{7}\times {\left(10.5\right)}^2 \\ \Rightarrow \mathrm{Surface}\mathrm{area}=4\times \frac{22}{7}\times 110.25 \\ \Rightarrow \mathrm{Surface}\mathrm{area}=88\times 15.75 \\ \Rightarrow \mathrm{Surface}\mathrm{area}=1386{\mathrm{cm}}^2 \end{gathered}$$

Hence, the surface area of sphere is $1386{\mathrm{cm}}^2$.