Question

The radius of curvature of a spherical mirror is 20 cm. What is its focal length?

Answer 1

We have,

R = 20 cm

Now ,if

f = R / 2 = 20 /2 = 10 cm

Answer 2

They parallel to the principle axis strike at a point ‘A’ on the mirror.

You have to make the any point on the spherical mirror with the line passing through center of curvature is taken.

As per the rules of reflection: angle of incidence = angle of reflection

Focal length of a spherical mirror = radius of curvature of a spherical mirror/2,

Focal length of a spherical mirror = 20cm/2,

Focal length of a spherical mirror = 10 cm