Flashcards
PHYS3051 - Resonators
Cards in this deck (6)
- 1How is the Q factor (quality factor) of a resonator defined?Q = 2*pi*(energy stored / energy lost per cycle)
Q = omega*(energy stored / rate of energy loss)
Q = omega_0 / gamma - 2What is the Q factor of a perfect resonator? What about for an instrument?Infinite, this will continue to resonate forever. For an instrument, Q factors tend to be on the order of 10^2.
- 3How does the oscillation of a resonator decay if no new energy is supplied?a(t) = a_0*exp(-gamma*t)*exp(-i*omega_0*t)
where the second exponent simply governs the up-and-down oscillation about the equilibrium position. - 4How are musical notes created?Standing waves are created in the medium. This is achieved through an impedance mismatch, occurring in strings as they encounter the contacting bridge/bolt and occurring in wind instruments at the interface to the atmosphere.
- 5What is gamma with reference to resonators?The fractional rate of power loss. Calculated as the FWHM of the Lorentzian (Fourier transform of the decaying exponential) or the inverse of thewidth of the decaying exponential. Can also be calculated using known data points in the equation by excluding the oscillation exponential.
- 6How are harmonics created in instruments?Harmonics involve having two standing waves which are integer multiples of each other playing at the same time. In string instruments this can be achieved by gently tapping on an already oscillating string.
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- Undergraduate - 3rd Year PHYS3051 - Fields in Physics Flashcards on PHYS3051 - Resonators, created by Curtis Browne on 17/06/2018.
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