JEE PYQ: Wave Optics Question 18
Question 18 - 2020 (07 Jan Shift 1)
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 the analyser need to be rotated further to reduce the output intensity to be zero, is:
(1) 71.6$°$
(2) 18.4$°$
(3) 90$°$
(4) 45$°$
Show Answer
Answer: (2)
Solution
According to question, the intensity of light coming out of the analyser is just 10% of the original intensity $(I_0)$.
Using, $I = I_0\cos^2\theta$
$\Rightarrow \frac{I_0}{10} = I_0\cos^2\theta \Rightarrow \frac{1}{10} = \cos^2\theta$
$\Rightarrow \cos\theta = \frac{1}{\sqrt{10}} = 0.316 \Rightarrow \theta \approx 71.6°$
Therefore, the angle by which the analyser need to be rotated further to reduced the output intensity to be zero
$\phi = 90° - \theta = 90° - 71.6° = 18.4°$
BETA
