Optics Question 205
Question: In Fresnel diffraction, if the distance between the disc and the screen is decreased, the intensity of central bright spot will
[RPMT 2002]
Options:
A) Increase
B) Decrease
C) Remain constant
D) None of these
Show Answer
Answer:
Correct Answer: B
Solution:
$ A=n\pi d\lambda $
$ \Rightarrow nd=\frac{A}{\pi \lambda } $ = constant
$ \Rightarrow n\propto \frac{1}{d} $
$ (n= $ number of blocked $ HPZ) $ on decreasing $ d, $
$ n $ increases, hence intensity decreases.
