First slide

Young's double slit Experiment

Question

Light reaches at a point P via two different paths(i) Direct (ii) After reflection from a plane mirror. Path difference between the two path is $\frac{5 λ}{2}$ , then the intensity at point P in terms of intensity due to source of light (I) is

Easy

A

2I
B

0
C

I
D

4I

Solution

Optical path difference when light directly comes = $\frac{5 λ}{2}$
Path difference when light comes after reflection $= \frac{5 λ}{2} + \frac{λ}{2} = \frac{6 λ}{2} \Rightarrow even multiple of \frac{λ}{2}$ so phase difference is 0 or 2 $π$
$I_{R} = 4 {Icos}^{2} \frac{ϕ}{2}, I_{R} = 4 I$

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