Question

A spherical mirror is having radius of curvature $20$cm. Determine its focal length if mirror is (a) concave and (b) convex.

Answer 1

Step 1: Finding the focal length of the concave mirror

A spherical mirror is having a radius of curvature $20$cm

The formula for finding the focal length of a concave mirror $=-\frac{\mathrm{Radius}\mathrm{of}\mathrm{curvature}}{2}$

$$\begin{gathered} =-\frac{20}{2} \\ =-10cm \end{gathered}$$

Step 2: Finding the focal length of the convex mirror

A spherical mirror is having a radius of curvature $20$cm

The formula for finding the focal length for a convex mirror $=\frac{\mathrm{Radius}\mathrm{of}\mathrm{curvature}}{2}$

$$\begin{gathered} =\frac{20}{2} \\ =10cm \end{gathered}$$

Hence, the focal length of the concave mirror is $-10cm$ and the focal length of the convex mirror is $10cm$.