The focal length of lens of refractive index `1.5` in air is `30 cm` When it is immersed in water of refractive index `(4)/(3)` ,then its focal length will be

Options

A. 0.15m
B. 0.30m
C. 0.45m
D. 1.20m

Answer

D

Explanation

`therefore (1)/(f)=[(mu_(1))/(mu_(2))-1][(1)/(R_(1))-(1)/(R_(2))]`
Given `R_(1)=0.30m,`
`R_(2)=-0.30m, mu_(1)=3//2, mu_(2)=4//3`
`[(1)/(f)=[(3//2)/(4//3)-1][(1)/(30)-((-1)/(0.30)]]`
By putting values, f=1.20m.