| Waves of similar, but different, frequencies superimpose to give patterns referred to as beats. The green and yellow waves superimpose in this way to give the red wave. Drag the green and yellow curves to on top of one another to convince yourself that these waves interfere constructively in some parts and destructively in other parts to give the red wave. The red wave is an example of a beat. Waves that are beats have a frequency that is the average (fAVG) of the frequencies of the incident waves. Drag the yellow and green waves to overlay the red one to convince yourself that the frequency of the red wave is between that of the yellow and green waves. Because the incident waves have regions where interference is constructive and regions where interference is destructive, the amplitude of the resultant wave varies from the sum of the amplitudes of the incident waves down to zero .Each section of the wave between the low amplitude regions is known as a beat. The frequency of these low amplitude regtions is fB/2 where fB is the difference between the frequencies of the incident waves. There are two beats per period of the amplitude modulation, and fB is referred to as the beat frequency. | MinusSinewave180x60 MinusSinewave180x60 MinusSinewave180x60 |