Earth: A Self-repairing Capacitor
One electrical device which serves as a model for
cosmic plasma activity is the capacitor, a device for accumulating and
storing electric charge.
A capacitor is
made of two conductors separated by an insulating medium.
When charge is placed on one conductor it attracts charge of
the opposite polarity on the other conductor. As a result,
an electric field is set up between the conductors, a
reservoir of electrical energy.
In both everyday electronics and advanced plasma
research the capacitor is important for its ability to rapidly store and
release electrical energy. Some of the highest energy experiments in the
world are performed using large rooms full of charged capacitors to
produce intense discharges.
As the charge on the capacitor increases, the
electric field between the conductors will increase, placing a growing
stress on the insulator. At some critical point, the insulator breaks
down and the capacitor "short circuits," releasing the stored electrical
energy suddenly. Such breakdowns may destroy a solid insulator and with
it, the capacitor.
However, if the charging rate is slow and the
insulator is air or liquid, the damage may repair itself as fresh
insulating material rushes in. That is a "self-repairing" capacitor. If
the current is strong or the insulator weak, current will pass between
the conducting plates, either steadily or in bursts. This is called a
Power transmission lines form large-scale
capacitors with the air as insulator between the conducting wires. The
geometry makes the electric field strongest at the wire surface, which
is where the air is likeliest to "break down" and discharge. The hissing
and crackling you hear when standing under a power line is just this
Many natural systems form capacitors as well. For
example, the Earth's surface and its ionosphere are two conducting
layers separated by air. The surface-ionosphere capacitor is of
particular interest in the study of sprites. Small "leaks" in the form
of lightning can trigger much larger "leaks" (sprites, etc.) at high
altitudes above them.
In the electric universe, this effect can be
traced via auroral circuits, through the circuitry of the solar system,
and far into interstellar space. From this viewpoint sprites and
lightning are merely leakage currents trickling off the galactic power
line. But clearly, the degree to which electric potential from the
galaxy powers thunderstorms on Earth has yet to be investigated.
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