Question 151: Wave Optics

Question

A plane polarized light is incident on a polariser with its pass axis aking angle $	heta $ with x-axis, as shown in the figure.  At four different values of $	heta ,\,	heta $ = 8
o
, 38
o
, 188
o
and 218
o
, the observed intensities are same.
What is the angle between the direction of polarization and x-axis ?
![](https://app-content.cdn.examgoal.net/fly/@width/image/1l7wzo54r/ce83a62c-0745-4c7b-b107-1ee4ae55a56c/b54bacb0-319f-11ed-b3ea-45214d807530/file-1l7wzo54s.png?format=png)

Accepted Answer

According to Malus law, we have
$I = {I_0}{\cos ^2}	heta  \Rightarrow {I \over {{I_0}}} = {\cos ^2}	heta $
Since the observed intensities are same for all values of $	heta$, therefore, for the angles given in options, the observed intensity should be same as well for all $	heta$, $	heta$ = 8$^\circ$, 38$^\circ$, 188$^\circ$ and 218$^\circ$, ${I \over {{I_0}}} \sim 0.9$; and for $	heta$ = 203$^\circ$, ${I \over I} \sim 0.9$.
Therefore, angle between direction of polarisation and x axis is 203$^\circ$.

Answer

98
o

Answer

128
o

Answer

203
o

Answer

45
o

Wave Optics

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