The practical unit is the volt-coulomb. As the volt is equal to 1E8
absolute units of potential and the coulomb to 0.1 absolute units of
quantity, the volt-coulomb is equal to 1E7 absolute units of energy.
The volt-coulomb is very seldom used, and the unit of Electric Activity
or Power (see Power, Electric), the volt-ampere, is universally used.
This unit is sometimes called the Watt, q. v., and it indicates the rate
of expenditure or of production of electric energy.
The storing up in a static accumulator or condenser of a given charge of
electricity, available for use with a given change of potential
represents potential electric energy.
The passing of a given quantity through a conductor with a given fall of
potential represents kinetic electric energy.
In a secondary battery there is no storage of energy, but the charging
current simply accumulates potential chemical energy in the battery,
which chemical energy is converted into electric energy in the discharge
or delivery of the battery.
It is customary to discuss Ohm's law in this connection; it is properly
treated under Electric Power, to which the reader is referred. (See
Power, Electric.)
[Transcriber's note: A volt-ampere or watt is a unit of power. A
volt-coulomb second or watt-second is a unit of energy. Power multiplied
by time yields energy.]
Energy, Electric Transmission of.
If an electric current passes through a conductor all its energy is
expended in the full circuit. Part of the circuit may be an electrical
generator that supplies energy as fast as expended. Part of the circuit
may be a motor which absorbs part of the energy, the rest being expended
in forcing a current through the connecting wires and through the
generator. The electric energy in the generator and connecting wires is
uselessly expended by conversion into heat. That in the motor in great
part is utilized by conversion into mechanical energy which can do
useful work. This represents the transmission of energy. Every electric
current system represents this operation, but the term is usually
restricted to the transmission of comparatively large quantities of
energy.
A typical installation might be represented thus. At a waterfall a
turbine water wheel is established which drives a dynamo. From the
dynamo wires are carried to a distant factory, where a motor or several
motors are established, which receive current from the dynamo and drive
the machinery. The same current, if there is enough energy, may be used
for running lamps or electroplating. As electric energy (see Energy,
Electric,) is measured by the product of potential difference by
quantity, a very small wire will suffice for the transmission of a small
current at a high potential, giving a comparatively large quantity of
energy. It is calculated that the energy of Niagara Falls could be
transmitted through a circuit of iron telegraph wire a distance of over
1,000 miles, but a potential difference of 135,000,000 volts would be
required, something quite impossible to obtain or manage.
[Transcriber's note: Contemporary long distance power transmission lines
use 115,000 to 1,200,000 volts. At higher voltages corona discharges
(arcing) create unacceptable losses.]