Question

The speed of light in air is 3 × 10^8 m/s. If the refractive index of glass is 1.5, find the time taken by light to travel a distance of 10 cm in the glass.

(a) 0.5 × 10^-10 s

(b) 5 × 10^-10 s

(c) 50 × 10^-10 s

(d) 500 × 10^-10 s

This question was addressed to me by my college professor while I was bunking the class.

Asked question is from Wave Optics in section Wave Optics of Physics – Class 12

Answer 1

Correct choice is (b) 5 × 10^-10 s

To explain I would say: vg = \(\frac {c}{\mu } = \frac {(3 \times 10^8)}{(1.5)}\) = 2 × 10^8 m/s.

Time, t = \(\frac {Displacement}{v_g}\)

t = \(\frac {(10 \times 10^{-2})}{(2 \times 10^8)}\)

t = 5 × 10^-10 s.