Question

The focal length of a spherical mirror is half of the radius of curvature

• A. For all rays
• B. Only for paraxial rays near the principal axis
• C. For those rays which are far from the principal axis
• D. For those rays which subtend extremely large angles with the axis

Answer 1

The correct option is B Only for paraxial rays near the principal axis

The rays that are near the principal axis (paraxial rays) and parallel to it converge to a single point on the axis after emerging from the spherical mirror. This point is called the focal point F of the lens.

And this is half of the radius of the curvature in spherical mirror.