Q. In Young’s double slit interference pattern the fringe width
A) Can be changed only by changing the wavelength of incident light
B) Can be changed only by changing the separation between the two slits
C) Can be changed either by changing the wavelength or by changing the separation between two sources
D) Is a universal constant and hence cannot be changed
Explanation
(c) Fringe width
$W = \frac{\mathrm{\Delta}\lambda}{d}$
If the screen is placed at a constant distance from the source, then
$W \propto \frac{\lambda}{d}$
Hence, fringe width can be changed either by changing the wavelength of light or by changing the separation between the two slits.
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.