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 polariod through $\;30^{0}\;$ makes the two beams appear equally bright . If the initial intensities of the two beams are $\;I_{A}\;$ and $\;I_{B}\;$ respectively ,then $\;\large\frac{I_{A}}{I_{B}}\;$ equals :
