question_answer

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 \[{{\text{I}}_{\text{A}}}\] and \[{{\text{I}}_{\text{B}}}\]respectively, then \[\frac{{{\text{I}}_{\text{A}}}}{{{\text{I}}_{\text{B}}}}\]equals :   JEE Main  Solved  Paper-2014

A) 1                                             

B) \[\frac{1}{3}\]

C)  3                                            

D)  \[\frac{3}{2}\]

E)

Correct Answer: B

Solution :

\[{{I}_{A}}{{\cos }^{2}}{{30}^{o}}={{I}_{B}}{{\cos }^{2}}{{60}^{o}}\]\[\Rightarrow \]\[\frac{{{I}_{A}}}{{{I}_{B}}}=\frac{1}{3}\]