Beat Frequency beat frequency is a fluctuating volume
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
Tuning a piano: • 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
Calculating beat frequency:
Example question: 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?
fb = = 20/4 = 5 Hz fb = │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
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