White light reflected at normal incidence from a soap film has minima at 6500 A ∘ and maxima at 7500 A ∘ in the visible region without minimum in between. If μ is 5 3 for the thin film, the thickness of the film is

Step-by-step solution

For minima to occur, 2 μ t = 2 n λ 1 2 ...(i) and for maxima 2 μ t = 2 n - 1 λ 2 2 ...(ii) From Equations. (i) and (ii), we get 2 n - 1 λ 2 = 2 n λ 1 or 2 n - 1 7500 = 2 n 6500 g i v e n ,   λ 2 = 7500   A ∘ ,   λ 1 = 6500   A ∘ or 15000 n - 7500 = 13000 n or 2000 n = 7500 or n = 3.75 Substituting the value of n in equation (i), we get 2 × 5 3 × t = 2 × 3.75 × 6500 2 × 10 - 10 ∵   μ = 5 3 ⇒