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A variation in the intensity of a composite wave which is formed from two distinct waves with different frequencies. Beats were first observed in sound waves, such as those produced by two tuning forks with different frequencies. Beats also can be produced by other waves. They can occur in the motion of two pendulums of different lengths and have been observed among the different-frequency phonons in a crystal lattice.
One important application of beat phenomena is to use one object with an accurately known frequency to determine the unknown frequency of another such object. The beat-frequency or heterodyne oscillator also operates by producing beats from two frequencies.
ii. When two waves are combined or superimposed, a beat occurs if two frequencies are not the same. Waves beat together to create the appearance of either a change in amplitude, if the frequencies differ by a few hertz (Hz), or new frequencies, called beat frequencies or heterodynes, if the original frequencies are far apart.