Practice question

**Interference** occurs when two coherent waves superpose, path difference Δ = d sinθ, bright fringe when Δ = n λ, n integer, seventh bright Δ=7λ, dark fringe Δ = (2n-1)λ/2, second dark Δ=3λ/2, third dark 5λ/2, sixth dark 11λ/2, distance of bright fringe from central y = n λ D/d, D screen distance, d slit separation, for λ=650 nm d=0.5 mm D=1.0 m fifth dark? Actually dark y=(2n-1)λ D/(2d). Dark fringe position x_n = ((n + (1/2)) λ D/d) . For the third dark fringe, n = 2 . λ = 5.5 × 10⁻⁷ m , d = 2.5 × 10⁻⁴ m , D =