The angular width of the central maximum in the Fraunhofer's diffraction pattern is measured. The slit is illuminated by the light of wavelength 6000 A ∘ . If the slit is illuminated by the light

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The angular width of the central maximum in the Fraunhofer's diffraction pattern is measured. The slit is illuminated by the light of wavelength 6000 A ∘ . If the slit is illuminated by the light of another wavelength, angular width decreases by 30 % . The wavelength of light used is

TestHub · Accepted Answer

For first diffraction minimum, d sin ⁡ θ = λ And if angle is small, sin ⁡ θ = θ d θ = λ i.e., Half angular width, θ = λ d Full angular width w = 2 θ = 2 λ d Also w ′ = 2 λ ′ d ∴ λ ′ λ = w ′ w or λ ′ = λ w ′ w = 6000 × 0.7 = 4200 Å

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