In Young's double slit experiment the distance between the two slits is 0.28 mm and the distance between the slits and the screen is 1.4 m. The distance between the central bright fringe and the third bright fringe is 0.9 cm. What is the wavelength of the light used?

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Accepted Answer

(1) 6000 A. Given: d = 0.28 mm = 2.8×10⁻⁴ m, D = 1.4 m, third bright fringe at x₃ = 0.9 cm = 9×10⁻³ m. Idea: the nth bright fringe of a two-slit pattern sits at xₙ = (nλ D)/d, so one measured fringe position fixes λ. Rearranged, λ = (xₙ d)/(n D), with n = 3 for the third bright fringe counted from the centre. λ = ((9×10⁻³)(2.8×10⁻⁴))/(3 × 1.4) = (2.52×10⁻⁶)/(4.2). λ = 6×10⁻⁷ m. That is 6000 A, an orange-red wavelength.

In Young's double slit experiment the distance between the two slits is 0.28 mm and the distance between the slits and the screen is 1.4 m. The distance between the central bright fringe and the third bright fringe is 0.9 cm. What is the wavelength of the light used?

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