Optics Question 882
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 the 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 _{A}}{I _{B}} $ equals
Options:
A) 3
B) $ \frac{3}{2} $
C) 1
D) $ \frac{1}{3} $
Show Answer
Answer:
Correct Answer: D
Solution:
[d] According to malus law, intensity of emerging beam is given by, $ I=I _{0}{{\cos }^{2}}\theta $
Now. $ {I _{A’}}=I _{A}{{\cos }^{2}}30^{o} $
$ {I _{B’}}=I _{B}{{\cos }^{2}}60^{o} $ As $ {I _{A’}}={I _{B’}} $
$ \Rightarrow I _{A}\times \frac{3}{4}=I _{B}\times \frac{1}{4}=\frac{I _{A}}{I _{B}}=\frac{1}{3} $
