Question

Define focal length​

Answer 1

Explanation:

the distance between the centre of a lens or curved mirror and its focus.

the equivalent distance in a compound lens or telescope.

Answer 2

Answer:

Focal length:-

It is the distance from the center of the lens the lens to the principal focal points of the lens.

For example:-

(A convex lens) the focal length is positive. and is the distance at which a beam of light will be focused to a single spot.

Hope it helps you.