When discussing the phenomenon of light diffraction at two slits, it is important to clarify that the presence or absence of air between the slits is not the determining factor for diffraction. Diffraction occurs when light encounters an obstacle or a narrow aperture, causing it to bend or spread out.
In the case of a double-slit experiment, where two closely spaced slits are used, light passing through these slits undergoes diffraction. The diffraction pattern is a result of the interference between the light waves that pass through each of the slits.
Even if there is no air between the slits, diffraction can still occur because light is a wave-like phenomenon. When light passes through each slit, it spreads out and creates a pattern of alternating bright and dark regions on a screen placed beyond the slits. This is known as an interference pattern.
The diffraction and interference patterns observed in a double-slit experiment are not solely dependent on the medium (such as air) between the slits but are intrinsic properties of wave behavior. The waves of light interfere with each other, leading to constructive and destructive interference, resulting in the characteristic pattern on the screen.
It's worth noting that while diffraction is commonly observed with light passing through small openings or slits, it is a general wave phenomenon that occurs with other types of waves as well, such as sound waves and water waves.