Practice portal › Wave Optics › Polarisation

Unpolarised light falls on two polarisers placed one on top of the other. What must the angle between the characteristic directions (optic axes) of the polarisers be if the intensity of the transmitted light is one third of the intensity of the incident light?

Asked in RS Academy GUJCET booklet · Malus's law and polaroids

• (1) 54.7°
• (2) 35.3°
• (3) 0°
• (4) 60°

Step-by-step solution

Why the other options are wrong

• (1) Comes from setting cos²θ=1/3, forgetting that the first polaroid has already halved the light: that gives θ=cos⁻¹1/(√3)=54.7°.
• (3) With the axes parallel the pair passes as much as it possibly can, (I₀)/2, which is more than a third.
• (4) cos²60°=1/4, so the light coming through would be (I₀)/8, not (I₀)/3.

Reading this solution needs no sign-in. You only sign in to practise against the clock and keep your progress.