80
The Body Electric
inside the nucleus. Although an electron is 1,836 times less massive
than a proton, the electron carries an equal but opposite (negative)
charge. Because of their lightness and their position outside the nucleus,
electrons are much more easily dislodged from atoms than are protons,
so they're the main carriers of electric charge. For the lay person's pur-
poses a negative charge can be thought of as a surplus of electrons, while
a positive charge can be considered a scarcity of them. When electrons
move away from an area, it becomes positively charged, and the area to
which they move becomes negative.
A flow of electrons is called a current, and is measured in amperes,
units named for an early-nineteenth-century French physicist, Andre
Marie Ampere. A direct current is a more or less even flow, as opposed
to the instantaneous discharge of static electricity as sparks or lightning,
or the back-and-forth flow of alternating current which powers most of
our appliances.
Besides the amount of charge being moved, a current has another
characteristic important for our narrative—its electromotive force. This
can be visualized as the "push" behind the current, and it's measured in
volts (named for Alessandro Volta).
In high school most of us learned that a current flows only when a
source of electrons (negatively charged material) is connected to a mate-
rial having fewer free electrons (positively charged in relation to the
source) by a conductor, through which the electrons can flow. This is
what happens when you connect the negative terminal of a battery to its
positive pole with a wire or a radio's innards: You've completed a circuit
between negative and positive. If there's no conductor, and hence no
circuit, there's only a hypothetical charge flow, or electric potential,
between the two areas. The force of this latent current is also measured
in volts by temporarily completing the circuit with a recording device,
as I did in my experiment.
The potential can continue to build until a violent burst of current
equalizes the charges; this is what happens when lightning strikes.
Smaller potentials may remain stable, however. In this case they must be
continuously fed by a direct current flowing from positive to negative,
the opposite of the normal direction. In this part of a circuit, electrons
actually flow from where they're scarce to where they're more abundant.
As Volta found, such a flow is generated inside a battery by the electrical
interaction of two metals.
An electric field
forms around any electric charge. This means that
any other charged object will be attracted (if the polarities are opposite)
or repelled (if they're the same) for a certain distance around the first