Question

A plane refracting surface of refractive index 3/2 is placed at a distance of 10 cm from a thin convex lens of focal length 30cm. The parallel rays incident on lens will converge at a distance of 

(1) 30cm from the lens 

(2) 25cm from the lens 

(3) 20cm from the lens 

(4) 40cm from the lens

Answer 1

Correct option (4) 40cm from the lens 

Explanation:

The lens will converge the rays as its focus i.e. 30 cm from refracting surface now 

PI₂ =μ (PI₁)

= (3/2 x 20)

= 30 cm

Hence rays will converge at a distance 40 cm from the lens.