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Re: Terry's Test - Two Manifestations of Charge

Original poster: "Antonio Carlos M. de Queiroz" <acmdq@xxxxxxxxxx>

Tesla list wrote:

Original poster: "David Thomson" <dwt@xxxxxxxxxxxx> 

This is very interesting.  The tube and plate are acting like a
capacitor.  That makes sense.  But wouldn't the capacitor act as
a transformer and reduce the potential in order to increase the
current?  In other words, the thinner spark would be higher
potential, lower current.  The thicker and brighter spark would
be lower potential, higher current.  The total power in each
spark would be the same, correct?


The potentials where the two sparks start are about the same,
as the two gaps are identical, and the shapes of the terminals
too. There is an asymmetry due to the different polarities of
the terminals, that causes some small difference.
The peak current in the brighter discharge is greater, because
it is generated by the discharge of a relatively large
capacitance, while the current in the weak spark is limited
by the electrostatic machine. The average powers in the sparks
are not identical:
Let the gap voltage v and the charging current i be fixed,
because the electrostatic machine acts as a current source.
The capacitance C is charged to v by i in a time T=Cv/i.
It then discharges the energy E=0.5Cv^2.
The average power in the strong spark is then 0.5Cv^2/T = 0.5vi.
In the weak spark a current i flows all the time (in average).
The power there is then vi.
So the average power in the weak spark is two times larger (?!).
But the peak power is much higher in the strong spark.
In the case of a Tesla coil, there are some differences, the most
important being the current through the capacitance between the
coil and the tube, that is in parallel with the weak spark, and
adds its current to the strong spark, as Terry demonstrated.
But the strong sparks are probably mainly caused by the high
peak currents of the discharge of the capacitance of the tube
to the ground.

Antonio Carlos M. de Queiroz