JEE Main · 2019 · 12 Jan 2019 · Shift 1 · EM Waves

A light wave is incident normally on a glass slab of refractive index 1.5 . If

4%

of light gets reflected and the amplitude of the electric field of the incident light is

30 V / m

, then the amplitude of the electric field for the wave propagating in the glass medium will be:

Answer: (C)

Solution

Intensity depends both on the square of the field amplitude and on the medium,

I \propto n E_{0}^{2}

, the refractive index entering through the energy speed in the medium. With

4%

of the light reflected,

96%

is transmitted into the glass, so taking the incident medium as air (

n = 1

n E_{0}^{'2} = 0.96 E_{0}^{2}

. With

n = 1.5

E_{0}^{'2} = \frac{0.96}{1.5} E_{0}^{2} = 0.64 E_{0}^{2}

, so

E_{0}^{'} = 0.8 E_{0} = 0.8 \times 30 = 24 V/m

JEE Main · 2019 · 12 Jan 2019 · Shift 1 · Single correct option