Question

A double-slit arrangement produces interference fringes for sodium light (λ = 589 nm) that are 0.20° apart. What is the angular fringe separation if the entire arrangement is immersed in water (n = 1.33)?

Answer 1

Data : θ₁ = 0.20°, n_w = 1.33

In the first approximation,

D sin θ₁ = y₁ and D sin θ₂ = y₂

This is the required angular fringe separation. 

OR

In the first approximation,