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soaps and grease.
potential barrier (semiconductor characteristic). The voltage in a semiconductor device on either side of
a PN junction. Free electrons from the N-material migrate across the junction to fill some of the holes in the
P-material. This migration causes a positive potential at the edge of the N-material, and a negative potential
at the edge of the P-material.
The potential barrier, sometimes called the potential hill, blocks any forward current flow across
the junction until the forward voltage is higher than that of the potential barrier. The potential barrier in a
silicon device is approximately 0.7 volt and approximately 0.3 volt in a germanium device.
potential difference. A difference in electrical pressure. A potential difference exists when one component,
or point, has an excess of electrons (a negative charge) and another has a deficiency of electrons (a positive
charge). Potential difference is measured in volts.
potential drop. A drop in voltage in an electrical circuit caused by current flowing through a resistance.
The amount of potential drop, which is also called a voltage drop or an IR drop, is determined by both the
current and the resistance.
potential energy. Energy possessed by an object because of its position, configuration, or the chemical
arrangement of its constituents.
potentiometer (electrical measuring instrument). An electrical instrument that measures the voltage of a
source without taking current from it. The unknown voltage is compared with an adjustable voltage that can
be accurately measured. When no current flows between the two voltage sources, they are exactly the same.
potentiometer (variable resistor). A variable resistor with three terminals, or connections. One connection
is made to each end of the resistance element, and a third connection is made to a wiper that can be moved
over the resistance element. The position of the wiper determines the amount of resistance used in the
circuit.
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 451
pot life (resin specification). The length of time a resin will remain workable after the catalyst has been
added. If a catalyzed material is not used within its usable pot life, it must be discarded and a new batch
mixed.
potted circuit. An electrical circuit in which all the components are protected by encapsulating them in an
insulating potting compound.
potting compound. A liquid plastic resin poured over electrical components in a potted circuit. The potting
compound cures into an insulating, rubber-like solid that protects the parts from moisture and physical
damage.
pound. A commonly used measure of weight or mass in the English system. One pound is equal to
approximately 0.454 kilogram.
poundal. A measure of force in the English system. One poundal is the amount of force needed to cause a
mass of one pound to accelerate at the rate of one foot per second each second it is acted upon.
pour point (petroleum product specification). The lowest temperature at which a material will pour
without assistance.
powdered-iron core (electrical component). A highly permeable core used in some electrical coils. The
core is made of fine particles of powdered iron, mixed with a suitable binder, and molded into the needed
shape. Powdered-iron cores have a high permeability and low eddy current losses.
power (electrical). The product of the applied voltage and the current in a DC circuit. In an AC circuit,
power is the product of the applied voltage and only that portion of the current in phase with the voltage.
The basic unit of electrical power is the watt, the amount of power used when one ampere of current is
forced through an electrical load under a pressure of one volt. One mechanical horsepower is equal to 746
watts of electrical power.
power (mechanical). The time rate of doing work. Power is found by dividing the amount of work done,
measured in foot-pounds, by the time in seconds or minutes used to do the work.
Power can be expressed in terms of foot-pounds of work per minute, horsepower, or watts. One
horsepower is equal to 33,000 foot-pounds of work per minute, 550 foot-pounds of work per second, or 746
watts. One metric horsepower is equal to 75 meter-kilograms of work per second or 0.9863 English
horsepower.
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航空术语词典Dictionary of Aeronautical Terms 中(177)
