First slide

Diffraction of light-Wave Optics

Question

A polarizer-analyser set is adjusted such that the intensity of light coming out of the analyser is just 10% of the original intensity. Assuming that the polarizer -analyser set does not absorb any light, the angle by which of the analyser need to be rotated further to reduce the output intensity to be zero is

Moderate

A

45º
B

71.6º
C

90º
D

18.4º

Solution

$\begin{array}{l} Let say incoming intensity to Analyser = I_{0} \\ and \\ outgoing intensity to Analyser = I \\ Then as per Malus' Law, I = I_{0} c o s^{2} θ \\ \Rightarrow \frac{I_{0}}{10} = I_{0} c o s^{2} θ \end{array}$
$\Rightarrow \cos θ = \frac{1}{\sqrt{10}} = 0.31$
$\Rightarrow θ = 71 . 6^{o}$

So, angle rotated should be = 90º-71.6º=18.4º

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