Two beams, A and B ,

Two beams, $\mathrm{A}$ and $\mathrm{B}$, of plane polarized light with mutually perpendicular planes of polarization are seen through a polaroid. From the position when the beam $\mathrm{A}$ has maximum intensity (and beam $\mathrm{B}$ has zero intensity), a rotation of polaroid through $30^{\circ}$ makes the two beams appear equally bright. If the initial intensitites of the two beams are $\mathrm{I}_{\mathrm{A}}$ and $\mathrm{I}_{\mathrm{B}}$ respectively, then $\frac{\mathrm{I}_{\mathrm{A}}}{\mathrm{I}_{\mathrm{B}}}$ equals :