Question

The intensity of a sound appears to an observer to be periodic. Which of the following can be the cause of it?

• A. The intensity of the source is periodic
• B. The source is moving towards the observer
• C. The observer is moving away from the source
• D. The source is producing a sound composed of two nearby fruequenices

Answer 1

Answer: (A), (D)

The intensity of the source is periodic
The source is producing a sound composed of two nearby fruequenices

The intensity of a sound appears to an observer to be periodic. So this can occurs because of the periodic intensity of the source.

We can't say the sound is periodic because the source is moving towards or away from the observer.

Also, the intensity of a sound appears to an observer to be periodic when a source produces a sound composed of two nearby frequencies because this gives rise to a phenomenon known as beats formation.