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Explain, with the help of a diagram, how plane-polarized light can be produced by scattering of light from Sun.

Two polaroids P1 and P2 are placed with their pass axes perpendicular to each other. Unpolarised light of intensity I is incident on P1 . A third polaroid P3 is kept between P1 and Psuch that its pass axis makes an angle of 45^{\circ} with that of P1. Calculate the intensity of light transmitted through P1,P2 and P3.

 
 
 
 
 

Answers (1)

The unpolarized light is incident on a molecule. To the plane of paper, the dots show vibrations perpendicular, and in the plane of the paper, the double arrows show Vibrations. The electron in the molecule begins to vibrate in both of these directions. The electrons vibrating parallel to the plane can't send energy towards an observes looking at 90^{\circ} to the direction of the Sun because their acceleration has no transverse component.

The light scattered by the molecules in this direction has only dots. It is polarized perpendicular to the plane of the paper. This explains the polarization of light scattered from the sky.

Now, the intensity of light transmitted by 1st polarised is, I_{1}=\frac{I}{2} 

The intensity of light transmitted by 2nd polaroid is,

I_{2}=I_{1}\cos ^{2}45^{\circ}= \frac{I}{2}\left ( \frac{1}{\sqrt{2}} \right )^{2}=\frac{I}{4}

The intensity of light transmitted by 3rd polarised is,

I_{3}=I_{2}\cos ^{2}(90-45)= \frac{I}{4}\left ( \frac{1}{\sqrt{2}} \right )^{2}=\frac{I}{8}

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