If Young’s double slit experiment is performed in water,
As the entire setup is in water, the wavelength will decrease by a factor 
.
Hence the fringe width becomes, 
. So, the fringe width decreases.
1
If Young’s double slit experiment is performed in water,
As the entire setup is in water, the wavelength will decrease by a factor .
Hence the fringe width becomes, . So, the fringe width decreases.