Question

What happens to the fringe pattern when the Young's double slit experiment is performed in water instead of air?

• A. Shrinks
• B. Disappear
• C. Unchanged
• D. Enlarged

Answer 1

Answer: (A)

In water, wavelength of light decreases by a factor $\mu$, the refractive index of water. In Young's double slit experiment, let screen is placed at a distance $D,d$ is the distance between coherent sources.

The fringe width is given by
$W=\frac{D\lambda }{d}$
where, $\lambda$ is wavelength of light used.
When the whole setup is dipped in water, wavelength is ${\lambda }_w=\frac{{\lambda }_a}{\mu }$ hence, it decreases.
Therefore, fringe width decreases and hence, fringe pattern shrinks.