Question

A convex lens of refractive index 3/2  has a power of 2.5 D in air. If it is placed in a liquid of refractive index 2, then the new power of the lens is

(a)  -1.25 D

(b)  -1.5 D

(c)  1.25 D

(d)  1.5 D

Answer 1

Correct option (a)  -1.25 D

Explanation:

Focal length of a convex lens having power 2.5 D, = 1/2.5 m

Also focal length of a lens in a medium of refractive index  μ is given by