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 IBIA equals:
(1) 3
(2) 23
(3) 1
(4) 31