Two beams, A and B, of plane polarized light with mutually

• Optics

Two beams, A and B, of plane polarized light with mutually perpendicular planes of polarization are seen through a polaroid. From the position when the beam A has maximum intensity (and beam B has zero intensity), a rotation of Polaroid through 30° makes the two beams appear equally bright. If the initial intensities of the two beams are I_A and I_B respectively, then I_A/I_B equals:

1. 1
2. 3
3. 3/2
4. 1/3

Answer

I_A cos² 30 = I_B cos² 60

I_A/I_B = 1/3

The correct option is D.