Question

If the thickness of a plate is 0.0032 cm, what shall be the phase retardation for a light of wavelength 5000 Å, given the principal refractive indices are 1.55 and 1.54?

(a) 1.05π radians

(b) 1.15π radians

(c) 1.25π radians

(d) 1.35π radians

The question was asked during an online exam.

This intriguing question originated from Retardation Plates topic in division Polarisation of Engineering Physics II

Answer 1

Right choice is (b) 1.15π radians

For explanation I would say: Here, t = 0.0032 cm, μe = 1.55, μ0 = 1.54 and λ = 5000 X 10^-8 cm

Phase retardation = \(\frac{2}{\pi\lambda}\)(μe – μ0)t

= 2π X 0.009 X 0.0032/5000 X 10^-8

= 1.15π radians.