Interference Questions

In a double slit experiment, when light of wavelength $400\text{nm}$ was used, the angular width of the first minima formed on a screen placed $1\text{m}$ away, was found to be $0.2^{\circ }$. What will be the angular width of the first minima, if the entire experimental apparatus is immersed in water? (${\mu }_{water}=4/3$)