Question

Suppose Young's double slit experiment is performed in air using red light and the interference pattern is shown on a screen. You then submerge the entire setup into water. What happens to the interference pattern? It disappears. The bright fringes are farther apart. The bright and dark fringes stay in the same locations but the contrast is reduced. No change happens in the interference pattern. The bright fringes are closer together.

Answer 1

Wavelength of the wave decrease as it enters into the water. Because wavelength is inversely proportional to the refractive index. Since $\mu$ of water is greater than air, hence wavelength will decrease and according to the relationship dsin$\theta$ = n$\lambda$, changes will occur accordingly.