Unpolarised light of intensity $I_0$ is passed through a single ideal polariser. The intensity of the transmitted light is:
- $I_0$
- $I_0/2$
- $I_0\cos^2\theta$
- $I_0/4$
Show answer and solution
Correct answer: B. $I_0/2$
Unpolarised light contains all polarisation directions with equal probability.
Averaging Malus's law over all input angles gives $\langle I \rangle = I_0 \langle\cos^2\theta\rangle = I_0/2$.
Once polarised, a second polariser would then attenuate further by $\cos^2\theta$ relative to its axis.