A polariser and an analyser are inclined to each other at 45°. The intensity of polarized light emerging from the analyzer is I, then the intensity of unpolarized light incident on the polariser is?
When an unpolarised light is incident on a polariser, its intensity is reduced by half. Then, if this polarized light passes through an analyzer inclined at an angle θ to the polarizer, the transmitted intensity is given by Malus’ law as $$
I= \frac {I_{unpol}}{2} cos^2θ
$$
Given θ= 45°
So, $$
I= \frac {I_{unpol}}{2} cos^245^°
$$
$$
I= \frac {I_{unpol}}{2}. \frac {1}{2} = \frac {I_{unpol}}{4}
$$
As the emerging intensity is I, so $$
\frac {I_{unpol}}{4} = I
$$
$$
I_{unpol} = 4I
$$
Therefore, the unpolarized light incident on the polarizer must have an intensity four times that of the polarized light emerging from the analyzer.