Beats are produced when two sound waves

  • A. of exactly the same frequency overlap
  • B. of slightly different frequencies overlap
  • C. travel in opposite directions
  • D. have very different amplitudes

Explanation

The two waves drift in and out of phase, so the loudness rises and falls at a rate equal to the difference between the two frequencies. A piano tuner uses this directly, tightening a string until the beats slow to nothing and the note matches the fork. Waves of exactly the same frequency give a steady sound rather than beats.

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