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

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 :

\[d=2{{f}_{i}}+{{f}_{2}}\]