Question

The radius of curvature of a thin plano-convex lens is 10 cm (of curved surface) and the refractive index is 1.5. If the plane surface is silvered, then it behaves like a concave mirror of focal length 

(a) 10 cm 

(b) 15 cm 

(c) 20 cm 

(d) 5 cm

Answer 1

Correct option: (c) 20 cm

Explanation:

The silvered plano convex lens behaves as a concave mirror; whose focal length is given by

If plane surface is silvered