Q factor

From TheBestLinks.com

The Q factor or quality factor is a measure of the "quality" of a resonant system. Resonant systems respond to frequencies close to the natural frequency much more strongly than they respond to other frequencies. On a graph of response versus frequency, the bandwidth is defined as the 3 dB change in level besides the center frequency. The definition of the bandwidth as the "full width at half maximum" or FWHM is wrong.

The Q factor is defined as the resonant frequency (center frequency) f₀ divided by the bandwidth Δf:

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Q = \frac{f_0}{f_2 - f_1} = \frac{f_0}{\Delta f} <math>

Bandwidth Δf = f₂ - f₁, where f₂ is the upper and f₁ the lower cutoff frequency.

In a tuned radio frequency receiver (TRF) the Q factor is:

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Q = \frac{1}{R} \sqrt{\frac{L}{C}} <math> where R, L and C are the resistance, inductance and capacitance of the tuned circuit, respectively.

In optics, the optical Q factor of a resonant cavity is the ratio of energy stored to energy dissipated in the cavity. If the Q factor of a laser's cavity is abruptly changed, the laser can be induced to emit a pulse of light; this technique is known as Q-switching.