Q: Discuss the intensity of transmitted light when a Polaroid sheet is rotated between two crossed polaroids ?
Sol: let I_0 be the intensity of polarised light after passing through the first polariser P1 . Then the intensity P2 will be
I = I2 cos2 θ, Where θ is the angle between pass axes of P1 and P2 .
Since P1 and P2 are crossed the angle between the pass axes of P2 and P3 will be (π/2- θ). Hence the intensity of light emerging from P3 will be
I = I0 cos2 θ cos2 (π/2-θ)
= I0 cos2 θ sin2 θ = (I0/4) sin2 2 θ
Therefore, the transmitted intensity will be maximum when 𝜃 = π⁄4.