JEE Main 2018 — Wave Optics Question with Solution

According to Malus law, we have

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

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$${}^{\circ }$$, $$\frac{I}{I_0}\sim 0.9$$; and for $$\theta$$ = 203$${}^{\circ }$$, $$\frac{I}{I}\sim 0.9$$.

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