Take two tuning forks of same frequencies and place them vertically on a hollow box. Now strike one of the two forks on a hammer containing rubber pad and then the other fork in the same way. It will be seen that almost similar continuous sound has been produced. Now strike the two forks simultaneously, it will be seen that these two forks are producing similar continuous sound: but the intensity of sound has increased significantly. Now add some wax on one arm of a tuning fork and make it heavier. Its frequency will decrease slightly and there will be a change in frequencies of the two tuning forks. Now if the two forks are struck simultaneously on a pad, you will observe this time sound is not continuous. Sound will be periodically faint and loud. This type of periodic variation of sound will be found if two tuning Corks of slightly different frequency are sounded together. This periodic variation of sound is called beat. Combination of one loud and one faint sound form a beat.
“Five beats per second are produced due to the interaction of two sounds”’- what does it mean?
It means the following things:
- Due to the action of two sound sources the intensity of sound rises and falls five times per second.
- The difference of frequencies between the sound sources, N = 5 Hz.
- Sound emitted from the two sources meet at a particular point or to ear 5 times in the same phase and 5 times in opposite phase.
- The time interval between the successive maximum and minimum intensity = 1/2n = 0.1 second.