For a thin convex lens when the heights of the object is double than its image, its object distance is equal to ....... Focal length of a lens is f.

Options

A. f
B. 2f
C. 3f
D. 4f

Answer

C

Explanation

`m=(h_2)/(h_1)=(h_2)/(2h_2)=1/2`
Accepting that image is inverted m =`-1/2`
`m=v/u=-1/2implies v=(-u)/(2)`
For mirror `1/f=(-1)/(u)+1/v`
`implies -u=3f`
(As per sign convention object distance is negative)