(a) Show, giving via suitable diagram, how unpolarized light can be polarised by reflection. (b) Two polaroids P1 and P2 are placed with their pass axes perpendicular to each other. Unpolarised light of intensity I0 is incident on P1. A third Polaroid P3 is kept in between P1 and P2 such that its pass axis makes an angle of 60° with that of P1. Determine the intensity of light transmitted through P1, P2 and P3.

(a) On reflection from a transparent medium a normal light beam becomes partially polarised. Higher the angle of incidence, higher the degree of polarisation. The reflected light beam becomes fully polarised at the polarising angle. Then μ = tan p where μ is the refractive index of the refracting medium and p is the polarising angle.
(b) Polaroids P1 and P2 have their axes perpendicular to each other and polaroid P3 is at 60° to P1. Intensity of light through P1, I′ = I0/2
Intensity of light through P3, I′′ = I′cos²(60°) = I0/2cos²(60°) = I0/8
Angle between P3 and P2 is 30°
Intensity of light through P2, I′′′ = I′′cos²(30°) = 3I0/32