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Question
In a double-slit experiment the angular width of a fringe is found to be 0.2° on a screen placed 1 m away. The wavelength of light used is 600 nm. What will be the angular width of the fringe if the entire experimental apparatus is immersed in water? Take refractive index of water to be 4/3.
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Solution
Distance of the screen from the slits, D = 1 m
Wavelength of light used, `lambda_1` = 600 nm
Angular width of the fringe in air θ1 = 0.2°
Angular width of the fringe in water = θ2
Refractive index of water, μ = `4/3`
Refractive index is related to angular width as:
μ = `θ_1/θ_2`
θ2 = `3/4 θ_1`
= `3/4 xx 0.2`
= 0.15
Therefore, the angular width of the fringe in water will reduce to 0.15°.
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