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 leng. The lens is placed at a distance d ahead of second wall, then the required focal length will be:

Options

A. Only `(d)/(4)`
B. Only `(d)/(2)`
C. More than `(d)/(4)` but less than `(d)/(2)`
D. Less than `(d)/(4)`

Answer

B

Explanation

The image of the same size is obtained at a distance d from the lens.
As `(I)/(o) =1=(v)/(u) therefore v=u`
For a convex lens, if u=2f, then v=2f
Thus, `d=2f therefore f=(d)/(2)`