Question

A point object is kept between a plane mirror and a concave mirror facing each other. The distance between the mirrors is 22.5 cm. The radius of curvature of the concave mirror is 20 cm. What should be the distance of the object from the concave mirror so that after two successive reflections the final image is formed on the object itself ? [Consider first reflection from concave mirror] : 

(A)  5 cm

(B)  15 cm

(C)  10 cm

(D)  7.5 cm 

Answer 1

Correct option  (B) 15 cm

Explanation:

Distance between object and cancave mirror 

First reflection from concave mirror :

it is negative

Image of concave mirror becomes object for plane mirror. Second reflection from plane mirror image is formed at same distance from plane as is the distance of object. Now according to question, second image is formed at object itself.

So :

x = 30

or 15 x = 30 is not possible,

so : x = 15