Question

In Young’s experiment, monochromatic light of wavelength 600 nm shines on two slits separated by 0.3 mm, producing an interference pattern on a screen that is 2.0 m away. You put a thin sheet of glass (n = 1.5) at the top slit and you observe a dark fringe the central location of the screen. Furthermore, the fourth bright spot on both sides of the central location is missing. (a) Sketch the resulting interference pattern. Precisely state the spacing between bright and dark fringes. Sketch up to and including the second order diffraction minimums. You must show all your numerical work. [4] (b) Find the width of the slits. [2] (c) Find the minimum thickness of the glass such that the central location of the screen is dark. [2] (d) Explain if the same pattern would be obtained if two independent sources of light, that is, using two separate lasers (one for each slit) would be used (instead of just one laser illuminating both slits). [2]

Answer 1

d). Two independent laser sources can't produce sustained interference pattern because they can't act as coherent sources which is the basic need of interference, due to not having constant phase difference. So a songle laser souce and produce interferce by producing two sources etger by reflection or refraction. But it can't be produced by independent laser sources though it is considered ideally coherent, I but we can use it as a source to produce interference to a certain extent to a approximation.