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. Remain unchanged

Answer 1

The correct option is B Decreases

When Young's double-slit set up for interference is shifted from air to within water then the fringe width decreases because the refractive index of water is more than that of the air.

Originally the fringe width is given by:

${\beta }_1=\frac{\lambda D}{2d}$

The new fringe width within water will be given by

${\beta }_2=\frac{\lambda D}{2nd}$

So,${\beta }_2=\frac{{\beta }_1}{n}$

Here, $n$ is the refractive index of medium