question_answer

A concave mirror of focal length \[{{f}_{1}}\] is placed at a distance of d from a convex lens of focal length \[{{f}_{2}}\]. A beam of light coming from infinity and falling on this convex lens concave mirror combination returns to infinity. The distance d must be equal                       [AIPMT (S) 2012]

A)  \[{{f}_{1}}+{{f}_{2}}\]         

B)       \[-{{f}_{1}}+{{f}_{2}}\]

C)  \[2{{f}_{1}}+{{f}_{2}}\]        

D)       \[-2{{f}_{1}}+{{f}_{2}}\]

Correct Answer: C

Solution :