Question

Two beams, $A$ and $B$, of plane polarized light with mutually perpendicular planes of polarization are seen through a polaroid. From the position when beam $A$ has maximum intensity (and beam $B$ has zero intensity), a rotation of polaroid through ${30}^{\circ }$ makes the two beams appear equally bright. If the initial intensities of the two beams are $I_A$ and $I_B$ respectively, then $\frac{I_B}{I_A}$ will be equal to

Answer 1

After passing through Polaroid,

$\text{Intensity of beam}A=\text{Intensity of beam}B$

$\Rightarrow I_A{\cos }^2{30}^{\circ }=I_B{\cos }^2{60}^{\circ }$

$\Rightarrow I_A\times \frac{3}{4}=I_B\times \frac{1}{4}$

$\therefore \frac{I_B}{I_A}=3$

Correct answer : $3$