1. Beat Frequency beat frequency is a fluctuating volume of sound it occurs when two sound waves of slightly different frequency are heard together constructive interference will produce an increase in loudness and destructive interference will produce a decrease in loudness the periodic change in intensity is called beats Beat Frequency Applet

2. An application of beat frequency can be seen with a piano. To tune a piano, strike a key and then compare the note with a tuning fork (i.e. known frequency) If the piano is slightly out of tune you will be able to hear the beat frequency Adjusting the piano wire until no beats are heard will mean the frequencies of the key and the tuning fork match Tuning a piano:

3. Calculating beat frequency:

4. When a tuning fork of unknown frequency is sounded simultaneously with a 512 Hz tuning fork, 20 beats are heard in 4.0 s. What are the possible frequencies of the unknown tuning fork? Example question:

5. f b = = 20/4 = 5 Hz f b = │f 1 – f 2 │ 5 = │512 – f 2 │ f 2 = 517 or 507 Therefore, the two possible frequencies for the unknown tuning fork are 507 Hz or 517 Hz. 7.9 Prac. #1,2 UC #1-3,5,6