Question

A lens is made of flint glass (refractive index = 1.5). When the lens is immersed in a liquid of refractive index 1.25, the focal length

(a) increases by a factor of 1.25

(b) increases by a factor of 2.5

(c) increases by a factor of 1.2

(d) decreases by a factor of 1.2

Answer 1

Correct option  (b) increases by a factor of 2.5

Explanation :

Let  f be focal length of lens.

Let f ' be focal length of the lens when immersed in a liquid.

i.e. focal length of lens when immersed in a liquid is increased by a factor of 2.5.