17.2

Beats

Student Notes

This simulation shows the beats that occur when two waves of different frequencies interfere with each other. The two individual waves are shown in green and blue, while their sum is shown in red. When you listen to beats you should understand that you're not hearing sound at that frequency (2 Hz is well below the range of human hearing, for instance), but you're hearing the intensity of the sound rising and falling at the beat frequency. Here are some things to investigate:

1. | The interference of waves is critical for understanding beats. Look carefully at the individual waves to see how they interfere to create the typical rising and falling beat pattern.
2. | How is the beat frequency determined?

Self-test

1. | When the beat is loud (i.e., has a large amplitude), is the interference between the two waves constructive or destructive?
2. | When the beat is soft (i.e., has a small amplitude), what kind of interference is taking place between the two waves?
3. | One wave has a frequency of 420 Hz and it interferes with a second wave to produce sound with a beat frequency of 8 Hz. Is this enough information to determine the frequency of the second wave?

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