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Question:

In a Young's double slit experiment, the spacing between the slits is 0.3 mm and the screen is kept at a distance of 1.5 m. The second bright fringe is found 6 mm from the central fringe. The wavelength of the light used in the experiment is?

625 nm

600 nm

550 nm

500 nm

Solution:

Given:
D = 1.5 m
d = 0.3 mm
2λD/d = 6 mm
=> λ = d × 6 / 2D nm
=> λ = 0.3 × 10⁻³ × 6 × 10⁻³ / (2 × 1.5 × 10⁹) nm
This gives,
λ = 600 nm