Question

a) Two narrow, parallel slits, separated by a distance of 0.25 mm, are illuminated by a light source whose wavelength is 480 nm. Calculate the angular separation of the central bright maximum and the first-order bright fringe.

b) Two narrow, parallel slits, separated by a distance of 0.25 mm, are illuminated by a light source whose wavelength is 480 nm.

(a) Calculate the angular separation of the central bright maximum and the first-order bright fringe.

(b) Calculate the linear separation of the central maximum and the first-order bright fringe, if the distance between the screen and the double-slit is 75 cm. .

Answer 1

The pattern obtained is an interference pattern. Given the distance between the slits d = 0.25mm = 0.25 x 10-3m and the wavelength of light = 480nm = 480 x 10-9m.

a) The angular seperation between central maxima and nth bright fringe is,

For first order, n = 1. Therefore,

So the angular separation of the central bright maximum and the first-order bright fringe is .

b) Given the distance between the slits and the screen is D = 75cm =0.75m. The position of nth bright fringe is given by,

For first order, n = 1. Therefore,

So the linear separation of the central maximum and the first-order bright fringe is 1.44mm.