When light passes through a double slit, it undergoes a phenomenon called interference, resulting in an observable pattern of light and dark regions on a screen placed behind the slits. This pattern is known as an interference pattern.
If you were to measure the intensity of light after it passes through a double slit and onto a screen, you would observe a series of bright and dark regions known as interference fringes. The intensity of light at different points on the screen can vary, with some regions appearing bright and others appearing dark.
This happens due to the wave nature of light and the interaction of the light waves from the two slits. Each slit acts as a new source of secondary waves that spread out and overlap with each other. This overlapping of waves leads to constructive interference (where waves combine and reinforce each other) and destructive interference (where waves cancel each other out) at different points on the screen.
At certain points on the screen, the waves from the two slits arrive in phase (constructive interference), resulting in bright fringes. At other points, the waves arrive out of phase (destructive interference), leading to dark fringes. The specific pattern of bright and dark fringes is determined by the spacing between the slits, the wavelength of light, and the distance between the screen and the double slit.
The interference pattern observed after light passes through a double slit is a clear indication of the wave nature of light and is one of the classic demonstrations of wave interference.