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Sum

In Young’s double-slit experiment, using monochromatic light, fringes are obtained on a screen placed at some distance from the slits. If the screen is moved by 5 x 10^{-2} m towards the slits, the change in the fringe width is 3 x 10^{-5} m. If the distance between the two slits is 10-3 m, calculate the wavelength of the light used.

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#### Solution

Here, ΔD = 5 x 10^{-2} m, Δβ = 3 ×10^{-5} m, d = 10^{-3} m, λ = ?

We know that fringe width in Young’s double-slit experiment is given by

`"β" = λ "D"/"d"`

Here, since λ and d are constant, we can write

`"Δβ" = λ/"d" "ΔD"`

∴ λ = `"Δβ"/"ΔD" d`

λ = `( 3 xx 10^-5 xx 10^-3)/(5 xx 10^-2)`

λ = `0.6 xx 10^-6 m xx 10^-7 m = 6000Å `

Concept: Interference of Light Waves and Young’s Experiment

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