A convex lens is placed in contact with a mirrorr as shown. If he space between them is filed with water, its power will

Options

A. decrease
B. increase
C. remain unchanges
D. can increse or decrease depending on the focal length

Answer

A

Explanation

`(1)/(F)=(2)/(f_l)+(1)/(f_m)=(2)/(f_l)+(1)/(infty)=(1)/(f_l)`
`(1)/(F')=(1)/(f_l)+(1)/(f_(omega))+(1)/(f_m)+(1)/(f_(omega))+(1)/(f_l)`
`=(2)/(f_l)+(2)/(f_(omega))+(1)/(infty)=(2)/(f_l)+(2)/(f_(omega))`
`f_(omega)` is `-ve`, `F' gt F`
Power decreases