

Distance of the screen from the slits (D) = 1 m
Wavelength of light (λ1) = 600 nm
Angular width of the fringe in air (θ1) = 0.2°
Angular width of the fringe in water = θ2
Refractive index of water (μ) = 4/3
Refractive index is related to angular width as:
μ = θ1/ θ2
θ2 = 3/4 θ1
= 3/4 x 0.2
= 0.15
Therefore, the angular width of the fringe in water will reduce to 0.15°.
