Define beats.

Explanation

Formation of beats: When two or more waves superimpose cach other with different slightly different frequencies, then a sound of periodically varying amplitude at a point is observed. This phenomenon is known as beats. The number of amnplitude maxima per second is called frequency. If we have two sources, then their difference in frequency gives the beat frequency. Number of beats per second
`n=|f_(1)-f_(1)| "per second"`