Page 48 - Electrical Engineering Dictionary

American standard code for information Ampere is best known for his pioneering
interchange (ASCII) a binary code com- work in the field of Electrodynamics. During
prised of seven digits, originally used to his emotionally troubled life, he held several
transmit telegraph signal information. professorships: at Bourg, Lyon, and at the
Ecole Polytechnic in Paris. While Ampere
ammeter an instrument for measuring worked in several sciences, the work of the
electric current in amperes. Danish physicist Hans Christian Oerstad on
the electric deflection of a compass needle, as
ammonia maser first maser, invented by demonstrated to him by Dominique Arago,
Charles H. Townes. Such a maser operates caused Ampere’s great interest in electro-
at microwave frequencies. magnetism. His seminal work, Notes on the
Theory of Electrodynamic Phenomena De-
ammonium dihydrogen phosphate (ADP) duced Solely from Experiment, established
a strong linear electro-optic material. Its the mathematical formulations for electro-
chemical formula is NH 4 H 2 PO 4 . See also magnetics including what is now known as
potassium dihydrogen phosphate (KDP). Ampere’s Law. It can be said that Ampere
founded the field of electromagnetics. He is
amorphous alloy a ferromagnetic mate-
honored for this by the naming of the unit of
rial with very low coercive force (i.e., a nar-
electric current as the ampere.
row hysteresis loop). The material is formed
as a very thin ribbon, by freezing the molting
amperometric sensor an electrochem-
alloy before it can crystallize, thus providing
ical sensor that determines the amount of
a random molecular orientation.
a substance by means of an oxidation–
reduction reaction involving that substance.
amortisseur winding See damper
Electrons are transferred as a part of the re-
winding.
action, so that the electrical current through
the sensor is related to the amount of the sub-
ampacity the maximum current which
stance seen by the sensor.
can be safely carried by a conductor under
specified conditions.
amplidyne a special generator that acts
like a DC power amplifier by using com-
ampere interrupting rating the inter-
pensation coils and a short circuit across its
rupting rating of a device expressed in amps
brushes to precisely and fastly control high
(often rms symmetrical amps). See also
powers with low level control signals.
MVA interrupting rating.
Ampere’s Law a fundamental rela- amplified spontaneous emission sponta-
neousemissionthathasbeenenhancedinam-
tionship in electromagnetic theory. In a
plitude and perhaps modified in spectrum by
fairly general form it is expressed by one of
propagation through an amplifying medium,
Maxwell’s equations,
usually the medium in which it was first gen-
∂D(r,t) erated.
∇× H(r,t) = + J(r,t)
∂t
where t is the time, r is the coordinate vector, amplifier a circuit element that has a
and the other vectors are defined as D(r,t) linear input-output signal relationship, with
electricdisplacement; H(r,t), magneticfield gain in voltage, current, and/or power. See
strength; J(r,t), electric current density. also balanced amplifier, feedback amplifier,
feedforward amplifier, laser amplifier, maser
Ampere, Andre Marie (1775–1836) amplifier, optical amplifier, single-ended
Born: Lyon, France amplifier.

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2000 by CRC Press LLC