Question

The given convex lens (refractive index ) is made to rest on the surface of a lake such that its upper surface is in air while the lower one is in water (refractive index ). Rays from the sun overhead converge at a distance a inside water, while rays from a luminescent angler fish beneath at the bottom of the lake converge at a distance b in air. Therefore 

(a)  a = 12 cm, b = 12 cm 

(b)  a = 24 cm, b = 12 cm 

(c)  a = 18 cm, b = 12 cm 

(d)  a = 24 cm, b = 18 cm 

Answer 1

Correct option  (d) a = 24 cm, b = 18 cm 

Explanation:

Since the two surfaces of the lens are in different media (air and water) we have to use refraction through curved surface formula. 

Radius of curvature of the lens :