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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 1 m 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? (μ_water = 4/3)

1. 0.266°
2. 0.15°
3. 0.05°
4. 0.1°

Correct answer: 0.15°

Solution

The angular width of the first minima is inversely proportional to the refractive index of the medium. Immersing the apparatus in water increases the effective refractive index, reducing the angular width. Using the relation θ_water = θ_air / μ_water, we get θ_water = 0.2° / (4/3) = 0.15°.

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