Question

Define the term 'focal length of a mirror'. With the help of a ray
diagram, obtain the relation between its focal length and radius of
curvature.​

Answer 1

Rays of light parallel to the principal axis of a concave mirror will appear to converge on a point in front of the mirror somewhere between the mirror's pole and its center of curvature. That makes this a converging mirror and the point where the rays converge is called the focal point or focus. Focus was originally a Latin word meaning hearth or fireplace — poetically, the place in a house where the people converge or, analagously, the place in an optical system where the rays converge. With a little bit of geometry (and a lot of simplification) it's possible to show that the focus lies approximately midway between the center and pole. I won't try this proof.

Answer 2

The distance from the pole to the focal point is called the focal length (f). The focal length of a spherical mirror is then approximately half its radius of curvature. It is important to note up front that this is an approximately true relationship.

The focal point of a lens or mirror is the point in space where parallel light rays meet after passing through the lens or bouncing off the mirror. A "perfect" lens or mirror would send all light rays through one focal point, which would result in the clearest image.

r=2f ( relation )

hope it helps u ...