Unpolarized light is incident on a polarizer. The light transmitted by the first polarizer is then incident on a second polarizer. The polarizing axis of the second polarizer is at 60º to that of the first polarizer.

The intensity emerging from the second polarizer is I_f.

Which of the following correctly gives the intensity incident on the first polarizer?

A. \(\frac{{{I_f}}}{8}\)

B. \(\frac{{{I_f}}}{4}\)

C. 4I_f

D. 8I_f

D

It is reasonable to expect higher level physics candidates to know the value of cos30°, and if they do not, they can always sketch the relevant triangle. The evidence from the statistics, though, would suggest that the majority of candidates either omitted to factor in the effect of the light passing through the first polarizer, or that they thought the intensity was reduced by the factor cos60º (rather than cos²60º) on passing through the second polarizer.