question_answer

A body is located on a wall. Its image of equal size is to be obtained on a parallel wall with the help of a convex lens. The lens is placed at a distance d ahead of second wall, then the required focal length will be:                        [AIPMT 2002]

A)              only \[\frac{d}{4}\]

B)                                               only\[\frac{d}{2}\]      

C)              more than \[\frac{d}{4}\] but less than \[\frac{d}{2}\]

D)       less than \[\frac{d}{4}\]

Correct Answer: B

Solution :

The lens formula can be written as

(i)

Given,

For equal size image

By sign convention,

or