NCERT Solution for Class 10 Science Chapter 10

Light – Reflection and Refraction

NCERT Books for Session 2022-2023

CBSE Board and UP Board

Intext Questions

Page No-168

Questions No-2

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

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Radius of curvature, R = 20 cm

Radius of curvature of a spherical mirror = 2 × Focal length (f)

R = 2f

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

Hence, the focal length of the given spherical mirror is 10 cm.

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Radius of curvature = 2 x focal length.

So, focal length = 1/2 × radius of curvature

=1/2×20 cm = 10 cm

Radius of curvature = 20 cm.

We know thatFocal length is equal to half of Radius of curvature. Therefore,Focal length = Radius of curvature / 2

= 20/2

= 10 cm

The focal length is10 cm.

Radius of curvature, R = 20 cm

R = 2f

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

The focal length is 10 cm.

Focal length = 2 x Radius of curvature = 2 x 20 cm = 10 cm

The relationship between the radius of curvature (R) and the focal length (f) of a spherical mirror is given by the mirror equation:

1/f = 1/R

In this equation:

» f is the focal length,

» R is the radius of curvature.

For a concave mirror (which has a positive radius of curvature), the focal length is considered negative.

Given that the radius of curvature (R) is 20 cm, you can substitute this value into the equation to find the focal length (f):

1/f = 1/20

Now, solve for f:

f = 20/1

Therefore, the focal length of the concave mirror is -20 cm. The negative sign indicates that the focal point is on the same side as the reflective surface (which is typical for concave mirrors).