Question

4) Define focal length​

Answer 1

Focal Length -

• The distance between the pole P of the concave mirror and the focus F is the focal length of the concave mirror.
• Thus, the focal length of a concave mirror can be estimated by obtaining a 'Real image' of a distant object at its focus, as shown in the figure.

Answer 2

$\underline\blue{Answer:-}$

Focal lenght and the distance from a focal point of a lens on mirror to the corresponding principal plane.