What is the relation between the focal length and radius of curvature of a spherical mirror (concave mirror or convex mirror) ? Calculate the focal length of a spherical mirror whose radius of curvature is 25 cm.

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Solution

For a spherical mirror the principal focus (F) lies exactly mid-way between the pole (P) and centre of curvature (C). So, the focal length (f) of a spherical mirror is equal to half of its radius of curvature (R).
f=R/2
R= 25cm (Given)
f=?
We know that
f=R/2
=25/2
f =12.5cm
So, focal Length is 12.5cm

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