Q. The maximum intensity of fringes in Young’s experiment is $I$. If one of the slit is closed, then the intensity at that place becomes $I_{o}$. Which of the following relation is true
A) $I = I_{o}$
B) $I = 2I_{o}$
C) $I = 4I_{o}$
D) There is no relation between $I$ and $I_{o}$
Explanation
(c) Suppose slit width’s are equal, so they produces waves of equal intensity say $I'$. Resultant intensity at any point $I_{R} = 4I^{'}\cos^{2}\phi$ where $\phi$ is the phase difference between the waves at the point of observation
For maximum intensity $\phi = 0{^\circ} \Rightarrow I_{\max} = 4I^{'} = I$ …(i)
If one of slit is closed. Resultant intensity at the same point will be $I'$ only, $i.e.,\ I^{'} = I_{O}$ …(ii)
Comparing equations (i) and (ii) we get
$I = 4I_{O}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.