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Capacitance vs Altitude (was Re: Variable Capacitance and Inductance)
Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>
Oddly, I have, in fact, measured the background "DC" E-field of the earth
(anyone who uses a radio measures a dynamic E-field, right?).. And, also
seen (as a child) a model airplane that used the differential voltage to
level the wings (quite a feat with components available in the 60's) (I have
to say, I'm not sure if it actually worked.. it was made by a student of my
Typical field at the surface is a few hundred volts per meter (1 kV/meter is
a nice working number). During thunderstorms it can rise up to 10-20 kV/m,
particularly right before a strike.
However, the voltage gradient isn't going to affect the capacitance, which
is almost entirely a function of geometry and material properties. The
corona fringing effect, if the plates are at high voltage, relative to
radius of curvature, will also change the apparent C.
There might be some very small relativistic effect as well due to the
slightly changed gravitational field. I don't recall enough about such
things to remember if the small bend in spacetime might cause a change in C.
Probably depends on frame of reference, and if the C measuring machine is in
the same frame as the C, it will read the same.
> Original poster: "rheidlebaugh by way of Terry Fritz <twftesla-at-qwest-dot-net>"
> Jim: I believe if you measure the electrostatic gradient of the earth you
> will be quite impressed how large the charge change with elevation is. The
> change is large enough to measure changes in cm of height from the earth
> surface. It has been used to control wing level on drone aircraft.
> Robert H