JEE MAIN - Physics (2018 - 15th April Evening Slot - No. 6)

A plane polarized light is incident on a polariser with its pass axis aking angle $$\theta $$ with x-axis, as shown in the figure. At four different values of $$\theta ,\,\theta $$ = 8o, 38o, 188o and 218o, the observed intensities are same.
What is the angle between the direction of polarization and x-axis ?
JEE Main 2018 (Online) 15th April Evening Slot Physics - Wave Optics Question 132 English
98o
128o
203o
45o

Explanation

According to Malus law, we have

$$I = {I_0}{\cos ^2}\theta \Rightarrow {I \over {{I_0}}} = {\cos ^2}\theta $$

Since the observed intensities are same for all values of $$\theta$$, therefore, for the angles given in options, the observed intensity should be same as well for all $$\theta$$, $$\theta$$ = 8$$^\circ$$, 38$$^\circ$$, 188$$^\circ$$ and 218$$^\circ$$, $${I \over {{I_0}}} \sim 0.9$$; and for $$\theta$$ = 203$$^\circ$$, $${I \over I} \sim 0.9$$.

Therefore, angle between direction of polarisation and x axis is 203$$^\circ$$.

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