Question

(a) The two polaroids, in a given set up, are kept ‘crossed’ with respect to each other. A third polaroid, now put in between these two polaroids, can be rotated. Find an expression for the dependence of the intensity of light I, transmitted by the system, on the angle between the pass axis of first and the third polaroid. Draw a graph showing the dependence of I on ϴ. (b) When an unpolarized light is incident on a plane glass surface, find the expression for the angle of incidence so that the reflected and refracted light rays are perpendicular to each other. What is the state of polarisation, of reflected and refracted light, under this condition

Answer 1

If intensity of unpolarized light on 1st polaroid = Io

Intensity of light that transmits by first polaroid = I 1 = Io / 2

By P3 = I 2 = I0 / 2 cos^2 θ

Angle b/w P 3 and P2 = 90 - θ

I3 = I2 cos ^ 2 θ ( 90 - θ ) = [ Io / 2 cos ^ 2 θ ] sin ^ 2 θ

Io / 8 [ 2 cos θ sin θ ]^2 = Io / 8 sin 2θ