Question

15. A virtual image three times the size of the object is obtained with a concave mirror of radius of curvature 36 cm. The distance of the object from the mirror is
(a) 20 cm (b) 10 cm (c) 12 cm (d) 5 cm

Answer 1

Option C 12 cm

It is given that,

Magnification

m=3

m=

u

−v

f=

2

R

=−18cm

It is given that a virtual image three times the size of the object is obtained with a concave mirror. So, v=−3u

From mirror’s formula

v

1

+

u

1

=

f

1

3u

−1

+

u

1

=

−18

1

u=−12cm

The distance of the object from the mirror u=12cm in front of concave mirror.

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Answer 2

Answer:

We are given the radius of curvature of the mirror, which is R = 36 cm. But since the mirror is concave, the radius of curvature will have a negative sign. Therefore, R = - 36 cm.

Explanation: