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Magnetism

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28 Feb 2007 13:15:26 IST

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Q-FACTOR

None

WAT IS Q-FACTOR PLZ GIVE ITS SIGNIFICANCE TOO.

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Kiran H

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Joined: 7 Nov 2006

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28 Feb 2007 15:26:37 IST

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The Q factor or quality factor compares the time constant for decay of an oscillating physical system's amplitude to its oscillation period. Equivalently, it compares the frequency at which a system oscillates to the rate at which it dissipates its energy. A higher Q indicates a lower rate of energy dissipation relative to the oscillation frequency. For example, a pendulum suspended from a high-quality bearing, oscillating in air, would have a high Q, while a pendulum immersed in oil would have a low one.

For an electrically resonant system, the Q factor represents the effect of electrical resistance and, for electromechanical resonators such as quartz crystals, mechanical friction.

BW or ?f = bandwidth

In a series LRC circuit, and in a tuned radio frequency receiver (TRF) the Q factor is:

$Q = \frac{1}{R} \sqrt{\frac{L}{C}}$ ,

where

R

L

and

C

are the resistance, inductance and capacitance of the tuned circuit, respectively.

Mechanical systems

For a single damped mass-spring system, the Q factor represents the effect of mechanical resistance.

$Q = \frac{\sqrt{M K}}{R}$

where M is the mass, K is the spring constant, and R is the mechanical resistance, defined by the equation

F d a m p i n g = ? R v

, where

v

is the velocity.

Optical systems

In optics, the Q factor of a resonant cavity is given by

$Q = \frac{2\pi f_o \mathcal{E}}{P}$ ,

where

f o

is the resonant frequency, $\mathcal{E}$ is the stored energy in the cavity, and $P=-\frac{dE}{dt}$ is the power dissipated. The optical Q is equal to the ratio of the resonant frequency to the bandwidth of the cavity resonance. The average lifetime of a resonant photon in the cavity is proportional to the cavity's Q. If the Q factor of a laser's cavity is abruptly changed from a low value to a high one, the laser will emit a pulse of light that is much more intense than the laser's normal continuous output. This technique is known as Q-switching.

Thats all about Q factor.

Cheers!

CyBorG

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Joined: 6 Jan 2007

Posts: 706

28 Feb 2007 15:35:47 IST

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Quality factor(Q-factor) is "the ratio of frequency corresponding to maximum current to the difference in frequencies at which max current reduces to 1/sqrt(2) of the max value"

It is 2pi times the energy stored in the circiut to the energy dissipated in resistance per cycle of ac supply.

It is also the ability of the circuit to differentiate between different frequencies of nearly equal magnitude.

Significance:Circuits having large Q-factors are more selective and have numerous applications in electronics eg tuning of a radio set to a particular frequency.There are many signals in air whose frequencies are close to each other.When we turn the knob of tuner we increase the capacitance in the circuit and thus resonance frequency of the LC circuit is adjusted till it matches with the frequency of the desired signal.Hence we can select the desired signal from a large number of signals of nearly same frequencies.

deepak_agarwal

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Joined: 9 Dec 2006

Posts: 634

1 Mar 2007 14:02:08 IST

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kab and kiran both have done their jobs to perfection an hence made my job easier

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