In a given region of 10 fringes are observed in the reflected beam from a thin film. If the wavelength of the incident light is changed from 4200 A ∘ to 6000 A ∘ , then the number of fringes observed in the same region will be

Question

In a given region of 10 fringes are observed in the reflected beam from a thin film. If the wavelength of the incident light is changed from 4200 A ∘ to 6000 A ∘ , then the number of fringes observed in the same region will be, 4, 7, 11, 3

MARKS App · Accepted Answer

Path difference 2 μ t cos ⁡ r = n λ Path difference is the same for both waves ∴ n 1 λ 1 = n 2 λ 2 Or n 2 = n 1 λ 1 λ 2 = 10 × 4200 6000 = 7

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