question_answer

A thin convex lens of focal length 'f is put on a plane mirror as shown in the figure. When an object is kept at a distance 'a' from the lens-mirror combination, its image is formed at a distance \[\frac{a}{3}\]in front of the combination. The value of 'a' is:

A) 3f 

B) \[\frac{3}{2}\]f 

C) f  

D) 2f