Question

A double convex thin lens made of glass (refractive index μ = 1.5) has both radii of curvature of magnitude 20cm. Incident light rays parallel to the axis of lens will converge at a distance d cm such that : 

(a) d = 20 

(b) d = 40 

(c) d = 10 

(d) d = 20/3

Answer 1

Correct option (a) d = 20

Explanation:

From lens maker’s formula

The incident light rays parallel to the axis of lens will converge at the focus. Hence, d = f = 20 or d = 20 cm