Question

If the radius of curvature of a concave mirror is $40cm$, its focal length will be

• A. $20cm$
• B. $40cm$
• C. $80cm$
• D. None of these

Answer 1

The correct option is A

$20cm$

Step 1 - Given data and formula.

The radius of the concave mirror is $R=40cm$
The formula for finding the focal length is $f=\frac{R}{2}$

Step 2 - Finding the focal length.

Substitute the value of $R$ into the formula to calculate the focal length.
$$\begin{gathered} f=\frac{R}{2} \\ f=\frac{40cm}{2} \\ f=20cm \end{gathered}$$

Final answer - Hence, option (a) is the correct answer.