Question

The radius of curvature of a spherical mirror is 40 cm.

Calculate its focal length.​

Answer 1

Answer:

focal length is 20cm

Explanation:

focal length is always equal to half of radius of curvature

Answer 2

Answer:

The radius of curvature of a spherical mirror is 40 cm, its focal length will be $20\ cm$ or $0.2\ m$

Explanation:

• For spherical mirrors having a small aperture, the radius of curvature is twice the focal length.

• Let R be the radius of curvature and f be the focal length then,

       $R = 2f$    ...(1)

• The distance from the pole to the center of curvature of the mirror is called the radius of curvature and focal length is the distance between the pole of the mirror and the focus of the object.

In the question, it is given that,

$R = 40\ cm = 40\times 10^{-2} m$

Using equation (1),

$f = \frac{R}{2}$

Substitute  the value of R,

 $f = \frac{40\times 10^{-2} }{2} = 0.2\ m = 20\ cm$