Question

How does the fringe width get affected, if the entire youngs double slit experiment is immersed in water?

Answer 1

On immersing the apparatus in a liquid(say water), the wavelength of light decreases.
That is :-
λ'=$\frac{\lambda }{\mu }$ ..............(1)
As fringe width is calculated by:-
β=$\frac{\lambda D}{2d}$ ........(1)
Put value of λ=λ'μ in eq.(1):-
Now:- β'=$\frac{\lambda }{\mu }$*$\frac{D}{2d}$
=β/μ'
That is fringe width decreases and hence becomes $\frac{1}{\mu }$ times of its value in air.