A biconvex lens made of a transparent material of refractive index 1.25 is immersed in water of refractive index 1.33. Will the lens behave as a converging or a diverging lens? Give reason.

Given: -

the refractive index of the given materials w.r.t air,

lens, =1.25

Water, =1.33

Calculations: -

The refaractive index of lens w.r.t water is,

The relative refractive index is 0.93 which is less than 1,

The lens makers formula for a biconvex lens gives,

Where, f and R are the focal length and the radius of curvature of the lens respectively

As the focal length is coming out to be negative, the lens would act as a diverging lens.