Question

If $s$ is the size of source giving light of wavelength $\lambda$ , separation between the slits, $D$ its distance from the plane of slits, what should be the criterion for the interference fringes to be seen.

Answer 1

The Young’s double slit experiment uses sources that are coherent in nature to understand the wave nature of the light. The light from the source is made to pass through two slits and made to fall on the screen. There indicates the formation of fringes.

Complete step by step solution:
It is given that the
size of source given light is $s$
wavelength of the light is $\lambda$
The distance between the slits is $D$
The interference fringes forms on the screen only when the certain criterion is established. In the young’s double slit experiment, the two slits act as the entrance of the light from the source of the light.
These two slits must be in equal size and at an equal distance from the centre to obtain the interference fringes on the screen. The size of the screen must be at $1\,mm$ wide. Hence the size of source given light is $s = 1\,mm$ . The source provides the light of the monochromatic and it must be nearly $10\,cm$ distance from the slit to obtain the formation of the fringes in the screen of the young’s double slit experiment.

Note: The source of the light used is coherent, that means it allows the light that has the same frequency and the same phase difference between the waves. That way the slits are placed at the equal distance from the centre and also the same size.