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 IA and IB respectively, then IA/IB equals:

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


IA cos2 30 = IB cos2 60

IA/IB = 1/3

The correct option is D.