## wave-optics Question 38

Question: Q. 4. Distinguish between polarized and unpolarized light. Does the intensity of polarized light emitted by a polaroid depend on its orientation ? Explain briefly.

The vibrations in a beam of polarized light make an angle of $60^{\circ}$ with the axis of the polaroid sheet. What percentage of light is transmitted through the sheet?

$\mathrm{R}$ [Foreign 2016]

## Show Answer

Solution:

Ans. If the direction of vibration of electric field vector/ plane of vibration of electric field vector, does not change with time, the light is polarized.

Whereas, if the direction of vibration of electric field vector / plane of vibration of electric field vector changes randomly in very short intervals of time / with time, the light is unpolarised. $1 / 2$

Alternatively,

Yes, it depends upon orientation of Polaroid because electric field vibrations, those are not in the direction of axis of Polaroid, are absorbed. Hence, intensity changes.

Alternatively,

$$ I=I_{0} \cos ^{2} \theta $$

$\theta=$ angle between vibration in light and axis of polaroid sheet)

$$ \begin{align*} I & =I_{0} \cos ^{2} 60^{\circ}=\frac{I_{0}}{4} \ \Rightarrow \quad \frac{I}{I_{0}} \times 100 & =\frac{1}{4} \times 100=25 % \end{align*} $$

[CBSE Marking Scheme 2016]