In question 118, if `m_(1)` and `m_(2)` are the magnifications for two positions of the lens, then

Options

A. `f=(d)/(m_(1)+m_(2))`
B. `f=(2d)/(m_(1)+m_(2))`
C. `f=(3d)/(m_(1)-m_(2))`
D. `f=(d)/(m_(1)-m_(2))`

Answer

d.

Explanation

As `m_(1)-m_(2)=(D+d)/(D-d)-(D-d)/(D+d)=(4Dd)/(D^(2)-d^(2))`
Hence, `m_(1)-m_(2)=(d)/(f)`
`f=(d)/(m_(1)-m_(2))`