Quality of a Tuning Fork

Consider a tuning fork tuned to middle C, 261.6 Hz 261.6 \text{ Hz} . If the sound intensity (proportional to the energy of oscillation) when the tuning fork is struck decreases by a factor of 4 in 6 seconds, what is the quality factor Q Q of the tuning fork to the nearest integer?


The answer is 7114.

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1 solution

Matt DeCross
Feb 22, 2016

If the sound intensity decreases by a factor of 4 in 6 seconds, then:

e 6 b / m = 1 4 . e^{-6b/m} = \frac14.

where b b and m m are the damping constant and mass of the tuning fork respectively treating it as a damped harmonic oscillator .

Taking the logarithm of both sides and rearranging,

m b = 6 log 4 . \frac{m}{b} = \frac{6}{\log 4}.

By the definition of the quality factor:

Q = m ω b , Q = \frac{m\omega}{b},

where ω \omega is measured in radians. Since ω = 261.6 Hz \omega = 261.6 \text{ Hz} , find:

Q = 6 log 4 ( 261.6 ) ( 2 π ) 7114. Q = \frac{6}{\log 4} (261.6)(2\pi) \approx 7114.

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