Question

A plane polarized light is incident normally on a tourmaline plate. Its $\overrightarrow{E}$ vectors make an angle of ${60}^o$ with the optic axis of the plate. Find the percentage difference between initial and final intensities.

• A. $25$%
• B. $50$%
• C. $75$%
• D. $90$%

Answer 1

The correct option is A $25$%

Let the initial intensity of the light be $I_o$.
Final intensity of the light $I=I_o{\cos }^2\theta$
where $\theta ={60}^o$
$⟹I=I_o\times {\cos }^2{60}^o=0.25I_o$
Percentage change in the initial and final intensities $=\frac{I_o-I}{I_o}\times 100=\frac{I_o-0.25I_o}{I_o}\times 100=75$ %
So option C is correct.