# Re: No collapsing magnetic field? (was Winding primary)

```Original poster: "Antonio Carlos M. de Queiroz" <acmq-at-compuland-dot-com.br>

Tesla list wrote:
>
> Original poster: "Randy & Lori" <rburney6-at-comcast-dot-net>
>
> I have to admit that the extent of my electrical background never reached a
> point where "parasitic capacitance" was addressed.

It's the same as distributed capacitance, that every conductor has
(in a Tesla coil, see the "self-capacitance" of the secondary coil and
the capacitance of the terminal).

> I never heard of
> "inductance of capacitors" and "capacitance of inductors" before studying
> TCs.

So you know that they exist.

> With your explanation below, I still don't see where your statement
> of "There is no collapsing magnetic field" is validated.

Magnetic field is always associated with current, in an instantaneous
way. It's one of Maxwell's laws. (Actually, things are a bit mor complex
because time-varying electric fields also produce magnetic fields.)
When I see the term "collapsing", I imagine something that happens
abruptly, but if you force the current in an inductor to stop, it never
does it instantaneously. This would require an infinite voltage applied
over the inductor. In a similar way, as was mentioned, the voltage over
a capacitor can't disappear instantaneously. This would require an
infinite current.

> As I understand how a coil
> works can be found at the following link.  If I have something wrong, I
> would like to know how; Like I said, my background never reached that of
> many on this list.

With some extra details (several web sites have pictures), what happens
is:
When the primary capacitor is charged to enough voltage, the gap
conducts
and the capacitor voltage is applied over the primary inductor. Current
starts to flow in the circuit. An analysis of the interaction between
the
primary capacitor and inductor, ignoring for awhile the secondary
circuit
and losses, reveals that the resulting current starts as a sinusoidal
waveform at the resonance frequency of the primary circuit. The
capacitor
voltage would be a cosinusoid at the same frequency.
Without the secondary circuit in place, the energy would be gradually
dissipated in the gap and other losses, and the sinusoidal current would
gradually decrease in amplitude and disappear after a few tens of
cycles.
With the secondary in place, resonating at the same frequency of the
primary, it starts to oscillate at the same frequency, and absorbs
energy from the primary circuit, reaching a point after some cycles
(how many depends on the coupling coefficient between the primary and
secondary inductances), where all the energy that was in the system
gets transferred to the secondary system. The current waveforms at
both circuits correspond to a sum of two sinusoids of different
frequencies, hence the name "energy transfer by double resonance".
When the energy transfer is complete, there is no energy left in the
primary circuit, and this instant is called "first notch". It's then
quite probable that the gap will cool down and cease to conduct,
"quenching". The energy is then trapped in the secondary system, where
it oscillates between the electric field in the distributed capacitance
of the secondary coil and terminal, and the magnetic field of the
secondary inductor. As the secondaty capacitance is much smaller than
the
primary capacitance, the voltage level reached is much greater than the
starting voltage at the primary capacitor (it's multiplied, ideally,
by sqrt(C1/C2)).
If the gap doesn't quench, the energy transfer proceeds in the reverse
direction, with the energy returning to the primary circuit in the same
number of cycles that it took in the first transfer. The process then
repeats, and there is again a second chance for trapping the energy in
the secondary, at the "second notch", and so on until all the energy
is dissipated, in losses or in sparks/streamers at the secondary
circuit.

Antonio Carlos M. de Queiroz

```