L A : Number of bright fringes = _________________ L B : Number of bright fringe

Question

LA: Number of bright fringes = _________________

LB: Number of bright fringes = _________________

In a setup like that in the figure below, a wavelength of 625 nm is used in a Young's double-slit experiment. The separation between the slits is d = 1.4 Times 10-5 m. The total width of the screen is 0.20 m. In one version of the setup, the separation between the double slit and the screen is LA = 0.24 m, whereas in another version it is LB= 0.54 m. On one side of the central bright fringe, how many bright fringes lie on the screen in the two versions of the setup? Do not include the central bright fringe in your counting.

Explanation / Answer

m y = d sin theta where y = wavelength = 6.25 * 10E-7 m-----------------------------Since tan theta = .1 / .24 = .417---------theta = 22.6 and sin theta = .385------------------So m (the number of bright fringes) = 1.4 * 10E-5 * .385 / 6.25 * 10E-7 = 8.7 (8 fringes)---------------------------In the second case tan theta = .1 / .54 = .185 and sin theta = .182 --------------------------------------Then m = 1.4 * 10E-5 * .182 / 6.25 * 10E-7 = 4 bright fringes

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