# Re: Now, How does a coil really work??

Hi folks...
One of the important parameters of a tuned circuit is it's 'Q'
The Q value can mean a lot of things - the ratio of 3db bandwidth to
centre freqency is the normal one, but it also means the length of time
for which the tuned circuit, when set into oscillation by a transient as
opposed to being continually pumped at a res. freq, will continue to
oscillate for before the oscillations die away due to system losses. I
cant remember this bit perfectly so maybe someone out there with a book
might be able to supply the appropriate info, but the Q of the tuned cct
= the number of oscillations before pretty much dying out ? 5%? 10%? of
original value. At any rate, if we for the moment assume this to be true
(it aint goona ring for too much more than this anyway) ie a tuned cct
with Q of 10 will basically ring through 10 oscillations, and our res.
frq = 2khz then the resonant oscillations will have all but died out in
around 5ms... thus resonant rise which takes a period of time noticeable
to a person is pretty unlikely.Also note the first bit... the bandwidth
- if the Q is very high, the bandwidth is very narrow - thus for a tuned
circuit which could  exhibit a resonant rise effect, the tuning between
primary and secondary would have to be really precise, and loading of
the output such as by drawing an arc may well detune it anyway, thus
diminishing the effect

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