Question

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

Answer 1

Answer: (C)

Fringe width $W=\frac{\Delta \lambda }{d}$
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.