The radius of curvature of a spherical mirror is $20cm$. What is its focal length?

Step 1: Given Data.

The radius of curvature of a spherical mirror, $r=20cm$

The focal length of a spherical mirror, $f=?$

Step 2: Formula Used.

The focal length of a given mirror is half of the radius of curvature of the same mirror.

$f=\frac{r}{2}$

Step 3: Calculation.

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

Hence, The focal length of the given mirror is 10 cm.