Difference between revisions of "Dictionary:Q(Quality)"

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See Figure [[Dictionary:Fig_A-2|A-2]].
See Figure [[Dictionary:Fig_A-2|A-2]].
[[File:Sega2.jpg|thumb|center|600px|'''Absorption terminology'''. Sometimes this terminology is used for attenuation because of factors other than absorption. ''E'' = energy, &Delta;''E'' = energy lost in one cycle, &lambda; = wavelength, ''f'' = frequency, ''x'' = distance, ''t'' = time, ''A''/''A''<sub>0</sub> = amplitude/(initial amplitude), ''A''<sub>1</sub>/''A''<sub>2</sub>=amplitude/(amplitude one cycle later).<ref>Sheriff, R, 1989, Geophysical methods: Prentice Hall Inc.</ref>]]
'''2'''. The ratio of the reactance of a circuit to the resistance.  
'''2'''. The ratio of the reactance of a circuit to the resistance.  

Revision as of 08:23, 30 December 2014

1. Quality factor, the ratio of 2π times the peak energy to the energy dissipated in a cycle; the ratio of 2π times the power stored to the power dissipated. The seismic Q of rocks is of the order of 50 to 300. Q is related to other measures of absorption (see below):

where V, f, λ, and T are, respectively, velocity, frequency, wavelength, and period.[1] The absorption coefficient α is the term for the exponential decrease of amplitude with distance because of absorption; the amplitude of plane harmonic waves is often written as

where x is the distance traveled. The logarithmic decrement δ is the natural log of the ratio of the amplitudes of two successive cycles. The last equation above relates Q to the sharpness of a resonance condition; fr is the resonance frequency and Δf is the change in frequency that reduces the amplitude by 1/√2. The damping factor h relates to the decrease in amplitude with time,

See Figure A-2.

2. The ratio of the reactance of a circuit to the resistance.

3. A term to describe the sharpness of a filter; the ratio of the midpoint frequency to the bandpass width (often at 3 dB).

4. A designation for Love waves (q.v.).

5. Symbol for the Koenigsberger ratio (q.v.).

6. See Q-type section.

See also


  1. Sheriff, R. E. and Geldart, L. P., 1995, Exploration Seismology, 2nd Ed., Cambridge Univ. Press.