Q. In Fresnel diffraction, if the distance between the disc and the screen is decreased, the intensity of central bright spot will
A) Increase
B) Decrease
C) Remain constant
D) None of these
Explanation
(b) $A = n\pi d\lambda \Rightarrow nd = \frac{A}{\pi\lambda} =$ constant
$\Rightarrow n \propto \frac{1}{d}(n =$ number of blocked $HPZ$) on decreasing $d,n$ increases, hence intensity decreases
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.