Question

What is the effect on the interference fringes in a Young’s double slit experiment when-
(a). The width of the two slits is increased
(b). The monochromatic source is replaced by a source of white light
(c). The separation between the two slits is increased, keeping other variables constant in each case?

Answer 1

Hint: For Young's double slit experiment, just a few orders of magnitude greater than the wavelength of light is used in two coherent light sources located at a short distance. The experiment of double-slits helped Young to understand light wave theory.

Complete step-by-step answer:
The laser illuminates similarly two parallel slit surfaces in an otherwise opaque surface in a modern version of Young's experiment, which vary fundamentally from the source of light only. On a distant screen you can see the light going across the two slits. The rules for geometric optics apply when the width of the slits is considerably greater than the wavelength of the light — light casts two shadows and two lit regions appear on the screen. The light diffracts into the geometrical shadow when the slits are narrowed in width and the light waves overlap on the screen.

The Young's initial double-slit experiment used a single source diffracted light and transmitted it to two additional slits to be used as coherent sources. For modern experiments, lasers are typically used as coherent light sources.
(a). The light intensity produced by the slits increases with increased width of the slit. The screen thus develops brighter fringes as the slit width increases.
(b). On the screen, coloured fringes will be created if the white light replaces monochromatic light.
(c).Fringe width $\beta = \dfrac{{\mu D}}{d}$. Therefore, the fringes are reduced by increasing the distance between the slits (d) and we then have narrower fronts.

Note: The Young's double-slit experiment was a turning point in the history of science, as the light was firmly established to be a wave. The experiment with double slits was subsequently performed with electrons and, to everyone's surprise, the pattern was the same with light as predicted.