What is interference of light? State any four conditions for obtaining well defined and steady interference pattern.

Answer:

Interference: The modification (redistribution) of intensity of light in the region where two or more coherent light waves overlap is called interference of light. Where the waves meet in phase the intensity is maximum (bright fringe, constructive interference) and where they meet in opposite phase it is minimum (dark fringe, destructive interference).

Conditions for a well-defined, steady pattern (any four):

1. The two sources must be coherent, i.e. they must maintain a constant phase difference (obtained from a single source).
2. The two sources must be monochromatic and emit light of the same wavelength (frequency).
3. The amplitudes (intensities) of the two waves should be equal or nearly equal, so that dark fringes are perfectly dark.
4. The two sources should be narrow (like fine slits) and close to each other.
5. The distance between the sources and the screen should be large compared with the distance between the sources, so that fringes are wide enough.
6. If the waves are polarised, they must be in the same state of polarisation; the background should be dark.