Two thin lenses of focal length `f_(1)` and `f_(2)` are in contact and coaxial. The power of the combination is

Options

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

Answer

D

Explanation

`(1)/(f_(eq)) = (1)/(f_(1)) + (1)/(f_(2)) rArr f_(eq) = (f_(1) f_(2))/(f_(1) + f_(2))`
Power (P) `= (1)/(f_(eq)) = (f_(1) + f_(2))/(f_(1) f_(2))` .