When an object is at distances x and y from a lens, a real image and a virtual image is formed respectively having same magnification. The focal length of the lens is

Options

A. `mu_(1) + mu_(2)/2`
B. `(mu_(1)-mu_(2))/2`
C. `(mu_(1) + mu_(2))/2`
D. `mu_(1) + mu_(2)`

Answer

C

Explanation

For real image `-m=f/(-u_(1)+f)`
or `m=(-f)/(-u_(1)+f)` …(i)
For virtual image
`m=f/(-u_(@)+f)`….(ii)
`:. (-f)/(-u_(1)+f)=f/(-u_(2)+f)`