Question

define focal length​

Answer 1

Answer:

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

Explanation:

Please mark me as brainlist and follow me

Answer 2

Answer:

For a thin lens in air, the focal length is the distance from the center of the lens to the principal foci (or focal points) of the lens. For a converging lens (for example a convex lens), the focal length is positive, and is the distance at which a beam of collimated light will be focused to a single spot.

Explanation:

Hope it helps you.. :)