Dave wrote:
"chuck" wrote in message
...
Dave wrote:
i have a feeling that what you will find is that the individual charges
on drops, flakes, and dust is too small to be detected by a normal
amateur receiver. However, the electric field that must accompany them
is what generates the corona effects that can be heard. Just think about
it, how do small particles get charged without also generating a larger
bulk field? The effect that charges the particles, be it dry friction
from wind on dust, or freezing and convection in clouds (any cloud, not
just those with enough charge to generate lightning) is not an individual
particle effect, it happens to many, many particles at once which
cumulatively create a much larger electric field than any one of them
alone could create. And while the charge transfer of small drops
striking a conductor may not be enough to stimulate a receiver the corona
caused by the accumulated field over the whole height of the structure
can be significant.
Charges can be accumulated on objects so as to produce a corona breakdown
in many ways. I think this is one of our fundamental starting points and
hopefully, was never in question. The separation of charges can be
accomplished by a variety of techniques, not all well-understood.
A moving cloud of charged particles can induce very large charges into a
grounded conductor. A sufficient concentration of charge at pointed
components of the conductor will produce a corona. The corona plainly
radiates "noise" that is detected by our receivers.
There is less certainty about whether an ungrounded conductor (say, an
unattached wire) can be made to produce a corona via electrostatic
induction. As I wrote in an earlier post in this thread, an ungrounded
conductor cannot be charged by an external field, but the distribution of
charges preexisting on the conductor can be affected by the field, perhaps
causing coronal discharges. I recall writing that uneven discharges of the
positive and negative "ends" of the conductor could even leave the
conductor with a net charge.
Your points are good ones, Dave, and worth keeping in mind.
floating conductors can definitely create corona. this can be seen in
corona camera pictures of power line insulators and other hardware that is
insulated but still in the high field near a power line. even water drops
on insulators can cause corona in a very strong field. and even if you get
away from power line stuff, a leyden jar has an insulated conductor and it
can obviously be charged, as can aircraft... and if they accumulate enough
charge they can cause corona.
Hi Dave,
A leyden jar is, of course, a capacitor. It is charged by grounding the
outside, applying a charge to the inside conductor, and then removing
the ground. Hope I didn't cause anyone to suspect that a capacitor could
not be charged that way.
Recall that in electrostatic induction, we always ground the conductor,
bring a field near it, and then remove the ground connection. A net
charge then remains on the conductor even after the inducing field is
moved away.
Aircraft can be and are regularly charged by the triboelectric effect.
The issue I raised is whether they can be given a net charge by
immersion in an electric field.
I also tried to explain that it is possible for a floating conductor to
produce a coronal discharge without that conductor having a net charge,
and followed with the suggestion that the act of producing a
differential coronal discharge might itself result in a net charge on
the conductor, but the corona can be produced by the field even when the
conductor is not charged. Your power line example may be a good example
of coronal discharge of a floating conductor in a strong field, but we
probably don't know if it ever had a net charge on it due to the field.
Hope this clarifies my thoughts a little. ;-)
73,
Chuck
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