Question

Two thin lenses of focal length `f_(1)` and `f_(2)` are in contact and coaxial. The power of the combination is
A. `sqrt((f_(1))/(f_(2)))`
B. `sqrt((f_(2))/(f_(1)))`
C. `(f_(1)+f_(2))/(f_(1)f_(2))`
D. `(f_(1)+f_(2))/(f_(1)f_(2))`

Answer 1

Correct Answer - D
If two thin lenses of focal lengths` f_(1)` and `f_(2)` are placed in contact coaxially, then equivalent focal length of combination is
`(1)/(F)=(1)/(f_(1)) + (1)/(f_(2))+(0)/(f_(1)f_(2))=(1)/(f_(1))+(1)/(f_(2))`
Power for the combination is
`P=(1)/(F)=(1)/(f_(1))+(1)/(f_(2))=(f_(1)+f_(2))/(f_(1)f_(2))`