Potential, Fall of.
The change in potential between any two points on an active circuit. The
change in potential due to the maintenance of a current through a
conductor.
The fall in potential multiplied by the current gives work or energy
units.
The fall of potential in a circuit and its subsequent raising by the
action of the generator is illustrated by the diagram of a helix. In it
the potential fall in the outer circuit is shown by the descent of the
helix. This represents at once the outer circuit and the fall of
potential in it. The vertical axis represents the portion of the circuit
within the battery or generator in which the potential by the action of
the generator is again raised to its original height.
In a circuit of even resistance the potential falls evenly throughout
it.
A mechanical illustration of the relation of fall of potential to
current is shown in the cut Fig. 269. A vertical wire is supposed to be
fixed at its upper end and a lever arm and cord at its lower end, with
weight and pulley imparts a torsional strain to it. The dials and
indexes show a uniform twisting corresponding to fall of potential. For
each unit of length there is a definite loss of twisting, corresponding
to fall of potential in a unit of length of a conductor of uniform
resistance. The total twisting represents the total potential
difference. The weight sustained by the twisting represents the current
maintained by the potential difference. For a shorter wire less twisting
would be needed to sustain the weight, as in a shorter piece of the
conductor less potential difference would be needed to maintain the same
current.
Fig. 269. MECHANICAL ILLUSTRATION OF FALL OF POTENTIAL AND CURRENT
STRENGTH.