Q factor

For other uses of the terms Q, Q factor, and Quality factor, see Q value (disambiguation).

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 high-quality bearing, oscillating in air, has a high Q, while a pendulum immersed in oil has a low one.

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 as the ratio of a resonator's centre frequency to its bandwidth when subject to an oscillating driving force.

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