Q factor
dimensionless measure for the damping of an oscillator
In physics and engineering, the quality factor or Q factor is a dimensionless parameter that describes how underdamped an oscillator or resonator is. Resonators with high quality factors have low damping, so that they ring or vibrate longer. For example, a pendulum suspended from a precision bearing, oscillating in air, has a high Q, while a pendulum immersed in oil has a low Q.
There are two definitions of Q that give numerically similar, but not identical, results. The more general definition is the ratio of the initial energy stored in the resonator to the energy lost in one radian of the cycle of oscillation. An alternative definition of Q factor, more applicable to high Q oscillators, is the ratio of a resonator's centre frequency to its bandwidth when subject to an oscillating driving force.
Explanation
The Q factor is a parameter that describes the resonance behavior of a damped harmonic oscillator (resonator). Sinusoidally driven resonators having higher Q factors resonate with greater amplitudes (at the resonant frequency) but have a smaller range of frequencies around that frequency for which they resonate; the range of frequencies for which the oscillator resonates is called the bandwidth. Thus, a high-Q tuned circuit in a radio receiver would be more difficult to tune, but would have more selectivity; it would do a better job of filtering out signals from other stations that lie nearby on the spectrum. High-Q oscillators oscillate with a smaller range of frequencies and are more stable.
The quality factor of devices varies substantially from system to system, depending on their function and design.
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