Question

Young's double slit experiment is performed in water instead of air, then fringe width

• A. decreases
• B. becomes infinite
• C. increases
• D. remains same

Hint:

Fringe width in YDSE is directly proportional to wavelength; higher refractive index means smaller wavelength and hence smaller fringes.

Answer 1

The Correct Option is A

Step 1: Formula for fringe width.
In Young’s double slit experiment, fringe width is given by \[ \beta = \frac{\lambda D}{d}, \] where \( \lambda \) is the wavelength of light in the medium, \(D\) is the distance between slit and screen, and \(d\) is the separation between the slits.
Step 2: Effect of medium on wavelength.
When the experiment is performed in water instead of air, the wavelength of light decreases because \[ \lambda_{\text{medium}} = \frac{\lambda_0}{\mu}, \] where \( \mu>1 \) is the refractive index of water.
Step 3: Conclusion.
Since fringe width is directly proportional to wavelength, a decrease in wavelength leads to a decrease in fringe width.