Part I. Interference of electromagnetic waves
When a number of waves pass through a point in a medium at the same time, they combine to produce a resultant wave a having different amplitude and hence intensity than the individual waves at that point. This process is known as the interference. The resultant intensity at a point is due to the combined influence of all the waves that pass through the point. Interference produces modification in the distribution of intensity of light. Interference have been observed with light waves, sound waves, water waves, etc. Interference can be explained using the principle of superposition of waves.
15.2 Conditions for sustained interference
To produce sustained interference, ...