Question

In Young’s double slit experiment, interference pattern will not be seen if one uses
A. A LASER as the source of light
B. Two LASER sources in front of two slits
C. Two sodium light lamps in front of two slits
D. In both (b) and (c) above

Answer 1

We know that Young’s double slit consists of two coherent sources of light that are placed small distance apart. The order of magnitude of light used is greater than the wavelength of light. To obtain interference patterns, the source of light should be coherent. Here, we will discuss the young’s double slit experiment and how coherent sources can be used to get the interference pattern.

Complete answer:
In Young's double slit experiment, a monochromatic source of light is placed at a considerable distance from the two slits. The source of light is equidistant from both the sources. A screen is placed at a certain distance from the slits.When the light passes through the slits, it gets divided and falls on the screen. It is possible only if using a single source of light because it can be made coherent by dividing the amplitudes or wave fronts.

But if we will use two physically different sources of light, they cannot be made coherent physically. Therefore, in Young’s double slit experiment, interference patterns will not be seen if one uses two LASER sources in front of two slits and two sodium light lamps in front of two slits.

Hence, option D is correct.

Note: The original Young’s double slit experiment uses diffracted light that is obtained from a single source of light. This diffracted light is then passed from the slits so that the slits can be used as coherent sources. In modern days, lasers are commonly used as coherent sources.