Peltier Effect.
The thermal effect produced by the passage of a current through the
junction of two unlike conductors. Such junction is generally the seat
of thermo-electric effects, and a current is generally produced by
heating such a junction. If an independent current is passed in the same
direction as that of the thermoelectric current, it cools the junction,
and warms it if passed in the other direction. In general terms,
referring to thermo-electric couples, if passed through them it tends to
cool the hot and heat the cool junction. The phenomenon does not occur
in zinc-copper junctions.
Peltier's Cross.
A bar of bismuth and a bar of antimony soldered centre to centre at
right angles, being notched or halved there to receive or to set into
each other. It is used to demonstrate the Peltier effect, q. v. To one
pair of ends are connected the terminals of a battery circuit; to the
other pair are connected the terminals of a galvanometer.
The galvanometer by its deflections in one and then in the other
direction indicates that the junction is heated when the current passes
from antimony to bismuth and vice versa. It thus illustrates the heating
and cooling of a thermo-electric junction by a current of electricity.
The current from the battery by the Peltier effect either heats or cools
the junction, as the case may be. This heating or cooling them produces
a thermo-electric current in the galvanometer circuit. The battery has
no direct influence on the galvanometer.
Pendant Cord.
A double conductor or pair of conductors, insulated from each other and
covered with a worsted, silk, or cotton covering and used to suspend
incandescent lamps and at the same time to conduct the current to them.
It is also used for other similar service, such as acting as conductors
for small motors. Often each conductor is composed of a number of thin
wires laid together. This gives flexibility to the cord.
Synonym--Flexible Cord.
Pendulum, Electric.
(a) A pendulum operated by the intermittent action of an electro-magnet,
whose circuit is opened and closed by the pendulum itself. A point at
the lower end of the pendulum swinging through a globule of mercury may
close and open the circuit. Various other methods of accomplishing the
same end are employed ..
(b) A pith ball suspended by a thread from an insulating stand. It is
used to show the attraction exercised by a piece of sealing wax or other
substance excited by rubbing.