Two motors in a factory are running at slightly different rates. One runs at 825.0 rpm and the other at $786.0 \mathrm { rpm } .$ You hear the sound intensity increase and then decrease periodically due to wave interference. How long does it take between successive instances of the sound intensity increasing?

Question

Quizplus · Accepted Answer

The beat frequency is the difference between the two frequencies, which is 825.0 rpm - 786.0 rpm = 39.0 rpm. Since 1 rpm = 1/60 Hz, the beat frequency is 39.0 rpm * 1/60 Hz/rpm = 0.65 Hz. The period of the beat is the reciprocal of the beat frequency, which is 1/0.65 Hz = 1.54 s.

Two Motors in a Factory Are Running at Slightly Different 786.0rpm.786.0 \mathrm { rpm } .786.0rpm.

Two Motors in a Factory Are Running at Slightly Different $786.0 \mathrm { rpm } .$