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Question:

In a double slit experiment, when light of wavelength 400 nm was used, the angular width of the first minima formed on a screen placed 1m away, was found to be 0.2°. What will be the angular width of the first minima, if the entire experimental apparatus is immersed in water?

0.266°

0.05°

0.1°

0.15°

Solution:

Correct option is B. 0.15°
In air angular fringe width is given by θ_0 = λ/D
Angular fringe width in water, θ_w = (λ/μ)/D = θ_0/μ=0.2°(4/3) = 0.15°
Hence option B is correct answer