Question

If a parallel beam of light is incident on spherical mirrors then after reflection they pass through focal point. If F is the focal length and R is the radius of curvature of mirror then

• A. \(R = F\)
• B. \(R = 2F\)
• C. \(R = F/2\)
• D. \(R = F/4\)

Hint:

For a spherical mirror the focus lies halfway between the pole and the centre of curvature.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
For a spherical mirror of small aperture, the focal point is at the middle of the line joining the pole and the centre of curvature.

Step 2: Detailed Explanation:
So \(F = \dfrac{R}{2}\), which means \(R = 2F\).

Step 3: Check the options.
\(R = F\) would put the focus at the centre of curvature, and \(R = F/2\) or \(F/4\) would put it beyond the centre.

Final Answer:
\(R = 2F\), option (B). \[ \boxed{R = 2F} \]