Question

what is the focal length of mirror explain. write 3 mark answer​

Answer 1

Answer:

Focal length.

Focal length (shown in red) is the distance between the center of a convex lens or a concave mirror and the focal point of the lens or mirror — the point where parallel rays of light meet, or converge.

Explanation:

MAY IT HELPS YOU

Answer 2

Answer: The focal length ( f ) is the distance from a lens or mirror to the focal point ( F ). This is the distance from a lens or mirror at which parallel light rays will meet.

So for the case of a concave mirror, it is the point at which all collimated (parallel) light rays entering the mirror being reflected and converged to a point in front of the mirror. The point of convergence (focus) is the focal point. As to how and why this is useful, the wikipedia page also touches on that.