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. 1D
B. `-1D`
C. `25 D`
D. `-25D`

Answer

A

Explanation

Power of lens = `mu_(2) - mu_(1) ((1)/(R_(t) - (1)/(R_(2)))`
in air power is -5D
`therefore -5 = (1.5 -1) ((1)/(R_(1)) - (1)/(R_(2)))` ……. (i)
In other medium power is P
`P = (1.5 - 1.6) ((1)/(R_(1))- (1)/(R_(2)))` ……. (ii)
Dividing (ii) by (i) `(P)/(-5) = (-0.1)/(1) xx (1)/(0.5) implies P = 1D`