A thin glass (refractive index 1.5) lens has optical power of `-5D` in air. Its optical power in a liquid medium with refractive index 1.6 will be

Options

A. `25 D`
B. `-25 D`
C. `1 D`
D. None of these

Answer

D

Explanation

`(f_(1))/(f_(a))=((._(a)mu_(g)-1))/((._(a)mu_(g)-1))`
`implies(f_(l))/(f_(a))=(._(a)mu_(g)-1)/(._(a)mu_(g)-1)=(1.5-1)/((1.5)/(1.6)-1)=(0.5xx1.6)/(-0.1)=-8`
`impliesP_(l)=(P_(a))/(8)=(5)/(8)`