Question

26) Radius of curvature of a mirror is 20cm, its focal length is

a. 4m

b. 40m

c. 0.25m

d. 10m
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Answer 1

Answer:

it should be d. 10cm, the units are either wrong or the options are wrong because in m it will be 0.1m

Answer 2

Answer:

Focal length of mirror is 10 cm.

Explanation:

Given,

Radius of curvature of a mirror is 20cm.

To find:  its focal length

Solution:

Radius of curvature is defined as the radius of sphere of which mirror is a part. and it can be given as:

Radius of curvature = 2 * focal length

or, R  = 2f

or, 20 cm = 2 * f

or, f = 20 / 2 = 10 cm

Therefore, Focal length of mirror is 10 cm.