Question

A concave mirror has radius of curvature of 0.4m ,calculate it's focal length

Answer 1

Answer:

given, radius of curvature = 0.4 m

focal length = radius of curvature /2

= 0.4/2

= 0.2 m

= 20 cm.

Answer 2

Focal length is 0.2 metres.

Given:

• Radius of curvature is 0.4 m

To find:

• Focal length of mirror ?

Calculation:

For paraxial light rays (i.e light rays which are close and parallel to the principal axis), the relation between radius of curvature and the focal length is:

$R = 2f$

• R is radius of curvature and f is focal length.

$\implies 0.4 = 2f$

$\implies f = \dfrac{0.4}{2}$

$\implies f =0.2 \: m$

$\implies f =20 \: cm$

So, focal length of mirror is 0.2 metres or 20 cm.