In a Young's Double slit experiment, first maxima is observed at … - Vidyadip

MCQ

In a Young's Double slit experiment, first maxima is observed at a fixed point $P$ on the screen. Now the screen is continuously moved away from the plane of slits. The ratio of intensity at point $P$ to the intensity at point $O$ (centre of the screen)

A
remains constant
B
keeps on decreasing
✓
first decreases and then increases
D
First decreases and then becomes constant

✓

Answer

Correct option: C.

first decreases and then increases

c
$I_{p}=\frac{I_{\max }}{2}[1+\cos \phi]=\frac{I_{\max }}{2}\left(1+\cos \frac{2 \pi y}{\beta}\right)$

where $\beta=D \lambda / d$.

First maxima is observed at $P$, i.e., cos. $\frac{2 \pi y}{\beta}$ should be negative. Hence, the ratio

$I_{P} / I_{\max }$ starts decreasing but starts increasing again as cos. $\frac{2 \pi y}{\beta}$ again starts becoming positive.

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