Question

A Young's double-slit set up for interference is shifted from air to within water, then the fringe width.

• A. Becomes infinite
• B. decreases
• C. increases
• D. remains unchanged

Answer 1

The correct option is B

decreases

Explanation

1. Fringe width is inversely proportional to the refractive index of the medium.
   $Fringewidth\propto \frac{1}{Refractiveindex}$
2. Therefore, the fringe width decreases with an increase in refractive index.
3. The refractive index of air is less than the refractive index of water.
4. When Young's double-slit setup for interference is shifted from air to glass, the fringe width decreases.

$Fringewidth=\frac{D\lambda }{\mu d}$ [ Where, $D$ is the distance between the screen and the slit, $d$ is the distance between the slits, $\lambda$ is the wavelength.]

Since, the refractive index of water is more than the refractive index of air, the fringe width decreases.

Hence, the correct option is $\left(B\right)$.