Circuit, Derived.
A partial circuit connected to two points of another circuit, so as to
be in parallel with the portion thereof between such two points; a shunt
circuit.
Synonyms--Shunt Circuit--Derivative Circuit--Parallel Circuit.
Circuit, Electric, Active.
A circuit through which a current passes. The circuit itself need only
be a conducting ring, or endless wire. Generally it includes, as part of
the circuit, a generator of electro-motive force, and through which
generator by conduction, ordinary or electrolytic, the same current goes
that passes through the rest of the circuit. One and the same current
passes through all parts of a series circuit when such current is
constant.
A current being produced by electro-motive force, and electromotive
force disappearing in its production in an active circuit, there must be
some source of energy which will maintain electromotive force against
the drain made upon it by the current.
The simplest conception of an active electric circuit is a ring or
endless conductor swept through a field of force so as to cut lines of
force. A simple ring dropped over a magnet pole represents the
simplification of this process. In such a ring a current, exceedingly
slight, of course, will be produced. In this case there is no generator
in the circuit. An earth coil (see Coil, Earth,) represents such a
circuit, with the addition, when experimented with, of a galvanometer in
the circuit.
In practice, a circuit includes a generator such as a battery or dynamo,
and by conductors is led through a continuous path. Electric lamps,
electrolytic cells, motors and the like may be included in it.
The term "circuit" is also applied to portions of a true circuit, as the
internal circuit, or external circuit. A certain amount of elasticity is
allowed in its use. It by no means necessarily indicates a complete
through circuit.
Circuit, Electrostatic.
(a) A circuit through which an electrostatic or high tension discharge
takes place. It is virtually an electric circuit.
(b) The term is applied also to the closed paths of electrostatic lines
of force.
Circuit, External.
The portion of a circuit not included within the generator.
Circuit, Grounded.
A circuit, one of whose members, the return circuit, is represented by
the earth, so that the earth completes the circuit. In telegraphy each
end of the line is grounded or connected to an earth-plate, q. v., or to
the water or gas-pipes, and the current is assumed to go through the
earth on its return. It really amounts to a discharging at one end, and
charging at the other end of the line. The resistance of the earth is
zero, but the resistance of the grounding or connection with the earth
may be considerable.
Synonyms--Ground Circuit--Earth Circuit--Single Wire Circuit.
[Transcriber's note: The resistance of the earth is high enough that
large power system return currents may produce dangerous voltage
gradients when a power line is shorted to the ground. Don't walk near
downed lines!]