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

Options

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

Answer

A

Explanation

`(1)/(f)=(1)/(f_(1))+(1)/(f_(2))=(f_(1)+f_(2))/(f_(1)f_(2))`, hence power of combination `P=(1)/(f)=(f_(1)+f_(2))/(f_(1)f_(2))`