A convex glass lens `(mu_(g) = 1.5)` has a focal length of 8 cm when placed in air. What is the focal length of the lens when it is immersed in water ?
`(mu_(omega) = (4)/(3))`

Options

A. 2 m
B. 4 cm
C. 16 cm
D. 32 cm

Answer

D

Explanation

`(1)/(f_(a)) = (n_(ga) - 1) ((1)/(R_(1)) - (1)/(R_(2)) )`
`(1)/(f_(w)) = (n_(gw) - 1)((1)/(R_(1)) - (1)/(R_(2)) ) `
`rArr (f_(w_))/(f_(a_)) = (1.5 - 1)/( (1.5)/(1.33) - 1)`
`rArr f_(w) = (0.5 xx 1.33 )/(1.5 - 1.33) xx 8 = 32` cm (approx.)