Problem 21.70 Piano tuners tune pianos by listening to the beats between the har
ID: 2228707 • Letter: P
Question
Problem 21.70 Piano tuners tune pianos by listening to the beats between the harmonics of two different strings. When properly tuned, the note A should have a frequency of 440 Hz and the note E should be at 659 Hz. Part B A tuner first tunes the A string very precisely by matching it to a 440 Hz tuning fork. She then strikes the A and E strings simultaneously and listens for beats between the harmonics. What beat frequency indicates that the E string is properly tuned? Express your answer with the appropriate units. Part C The tuner starts with the tension in the E string a little low, then tightens it. What is the frequency of the E string when she hears four beats per second? Express your answer with the appropriate units.Explanation / Answer
A. 3rd harmonic of A = 440 x 3 = 1320Hz ....2nd harmonic of E = 659 x 2 = 1318Hz (Target frequency) Beat frequency = 1320 - 1318 = 2Hz (when properly tuned) B. When beat frequency is 4Hz frequency of E string = 1320 - 4 = 1316Hz.
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