Question

The radius of curvature of a convex mirror is $40cm$. Find its focal length.

• A. $80cm$
• B. $40cm$
• C. $20cm$
• D. $10cm$

Answer 1

Answer: (C)

$20cm$

The relationship between the radius of curvature and focal length is that the radius of curvature is twice the focal length. In other words, focal length is half the radius of curvature.
In this case, radius of curvature of the concave mirror is given as 40 cm. Hence, the focal length of the mirror is $\frac{40}{2}=20cm$.
Hence, the focal length of the concave mirror is $20cm$.