Question

Unpolarised light of intensity 32 wm–2 passes through three polarisers such that the transmission axis of the last polariser is crossed with first. If the intensity of the emerging light is 3wm–2, the angle between the axes of the first two polarisers is

Answer 1

intensity after first polariser = 32/2 = 16 W m-2

let angle between 1st and 2nd polariser is theta so intensity = 16 {cos(theta)}^2

angle between 2nd and 3rd = 90-theta

so intensity   3 Wm-2 = 16 {cos(theta)}^2 * { cos (90-theta)}^2

3 = 4 { 2cos (theta) * sin(theta) }^2

3/4 = { sin (2*theta)}^2

squrt(3) / 2 = sin (2*theta)

sin 60 = sin (2*theta)

2*theta = 60

theta = 60/2 = 30 degree

angle is of 30 degree between first two polarisers.

Answer 2

Answer:

Explanation:

Given is,

light of intensity 32 wm–2

intensity of the emerging light is 3wm–2,

Angle between two axis=

solution :

Let the angle between two Axis=θ

If the angle between the axes of the first two polarisers is, then the angle between the second and third polarisers is obviously (90 - θ)

I= I 0/2cos 2θcos 2 (90 −θ)

or 2= 32/2=cos 2 θcos 2(90o −θ)16cos 2 θsin

(2sinθcosθ) 2 = 1/2

2θ=45 orθ=22.5o