In an experiment, two polarizers are arranged such that the angle between their pass axes is 30°. If the intensity of light after passing through the first polarizer is 10 mW/m2, then what is the intensity of light after passing through the second polarizer?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → 7.5 mW/m2
Light leaving the first polarizer is plane polarized. The second polarizer passes only the component along its own axis, so by Malus’ law the intensity is multiplied by \( \cos^{2}\theta \), where \( \theta \) is the angle between the pass axes.
\( \displaystyle I = I_0\cos^{2}\theta = (10\,\mathrm{mW/m^{2}}) \times \cos^{2}30^\circ \)
\( \displaystyle I = 10\,\mathrm{mW/m^{2}} \times \left(\frac{\sqrt{3}}{2}\right)^{2} = 10\,\mathrm{mW/m^{2}} \times \frac{3}{4} \)
\( I = 7.5\,\mathrm{mW/m^{2}} \)