Question

Distance between two slits in youngs experiment is 0.1mm.d=1.5m wavelength is 6000å.calculate distance between third bright and fifth dark fringe

Answer 1

Answer:

Let y = wavelength, d = .1mm, D = 1.5 m  and S = separation

3 y = d sin theta1      third bright fringe not counting central maximum

(4 + 1/2) y = d sin theta2         since m = 0 for first dark fringe

1.5 y = d (sin theta2 - sin theta1) = d (theta2 - theta1)  since theta is small

S = D (theta2 - theta1) = D * 1.5 y / d

S = 1.5 *  1.5 *6 * 10E-7 / 1 * 10E-4

S = 2.25 * 6 * 10E-3 = 1.4 * 10E-2 m = 14 mm