Talk:Q factor

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[edit] FWHM vs 3dB

The article states:

the bandwidth is defined as the 3 dB change in level besides the center frequency.

The definition of the bandwidth BW as the "full width at half maximum" or FWHM is wrong.

Unless the definition depends on the slight difference between -3dB (1/1.995) and half maximum (1/2), this would seem to be the same thing. Anyone know for sure, here? -- DrBob 17:57, 27 Sep 2004 (UTC)

Strictly, the FWHM is full width at half-max, that is half power. In dB this is -3.01 dB, close enough to 3 dB down to not worry about it.

The definition "In optics..." appears strange to me. In mechanics the Q factor can be shown to be equal to 2 * Pi times the energy stored in the oscillator divided by the energy dissipated per cycle. I suspect this is the correct definition, applicable to optics, mechanics, and any other oscillating system.

24.245.15.183

I suspect you're absolutely correct about the definition applying to all oscillating systems. "Q-switching", though, is a very real phenomenon and used to great advantage in pulsed laser systems.

By the way, you can easily sign your "talk" posts by appending four tildes (~~~~) to the posting. When you "Save changes", this will be replaced by your username in a handy linked form and a timestamp of your edit.

Atlant 14:27, 10 August 2005 (UTC)

Alison Chaiken 00:00, 23 September 2005 (UTC): I've always thought of the quality factor as the number of cycles that it takes for energy to be dissipated from the system. Thus a Q of 1000 means that the excited oscillation will ring down to zero in 1000 cycles. I would think this article should mention this insight. I would add it except that I can remember if Q is the number of cycles to ring down to 1/2 the original energy or what exactly.

No, that's wrong. It never decays to zero. The article states correctly that it's the number of cycles required to decay to 1/535 of its original energy.--24.52.254.62 01:25, 21 October 2006 (UTC)