Two polarizing sheets have their transmission axes parallel so that the intensity of unpolarized light transmitted through both of them is a maximum. Through what angle must either sheet be rotated if the transmitted intensity is 25 % of the incident intensity?
A)15°
B)30°
C)45°
D)60°
E)75°

Question

Quizplus · Accepted Answer

When the intensity of light transmitted through both polarizing sheets is a maximum, the axes of both the sheets are parallel. Let the unpolarized light have an intensity I. Therefore, the intensity of light transmitted through both sheets is I/2.
When one of the sheets is rotated through an angle θ, the intensity of the transmitted light is reduced to (I/4) cos²θ.
We need to find the angle through which either sheet must be rotated to reduce the intensity to 25% of the incident intensity.
So, (I/4) cos²θ = I/4
cos²θ = 1/4
cosθ = 1/2
θ = 60°
Therefore, either sheet must be rotated through an angle of 60°.

Two Polarizing Sheets Have Their Transmission Axes Parallel So That