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:
a. 3
b. 23
c. 1
d. 31