Question

a) In a single slit experiment, suppose you want to make the first dark spot disappear from practical measurement (you can't see it anymore). What could you do?

b) In single slit experiment you want to make the dark "smudges" or dark spots closer to the center, what two things could you do?

c) In a double or multiple slit experiment, you almost always see dark smudges on either side of the center. Why is that? What are the dark smudgs from? How could you devise a double slit experiment that eliminates the dark smudges but retains the double slit interference pattern? PLEASE EXPLAIN ALL WORK WITH APPROPRIATE EQUATIONS

Answer 1

(a) In a single slit experiment, the general formula is , where a is slit width, is the angle light makes with direction of symmetry, is the wavelength, n is the order of a minima. For first minima, n=1. So, .....(1).

This minima occurs when lights from upper and lower half points of the slit interfere destructively. To make this spot disappear, destructive interference has to be stopped.

(b) Refer to equation (1) above.

To make dark spots closer to the center, the slit width a has be made larger. In that case, the pateerns will get closer to the center.

(c) Dark smudges appear on either side of the center because of destructive interference. Light from one slit travels a distance that is ½ wavelength longer than the distance traveled by light from the other slit. When crest of one interferes with trough of another, destructive interference happens.  The dark fringes are followed by the first-order fringes, one on each side of the center.

Dark smudges appear from destructive interference.