GROUND POTENTIAL-- Zero potential with
HYSTERESIS LOSS-- The power loss in an iron-core
respect to the ground or earth.
transformer or other ac device as a result of
HALF-CELL-- One of the electrodes and its
immediate environment in an electrochemical cell;
INDUCED CURRENT-- Current due to the relative
an electrode and environment arranged for the
motion between a conductor and a magnetic field.
passage of current to another electrode for the
INDUCED ELECTROMOTIVE FORCE-- The
measurement of its electrode potential; when
electromotive force induced in a conductor due to
coupled with another half-cell, an overall cell
the relative motion between a conductor and a
potential develops that is the sum of both half-cell
magnetic field. Also called induced voltage.
INDUCED REACTANCE (XL)-- The opposition to
HENRY (H)-- The electromagnetic unit of inductance
the flow of an alternating current caused by the
or mutual inductance. The inductance of a circuit is
inductance of a circuit, expressed in ohms.
1 henry when a current variation of 1 ampere per
INSULATION-- (1) A material used to prevent the
second induces 1 volt. It is the basic unit of
leakage of electricity from a conductor and to
inductance. In radio, smaller units are used, such as
provide mechanical spacing or support to protect
the millihenry (mH), which is one-thousandth of a
against accidental contact. (2) Use of material in
henry (H), and the microhenry
which current flow is negligible to surround or
one-millionth of a henry.
separate a conductor to prevent loss of current.
HERTZ (Hz)-- A unit of frequency equal to one cycle
INTERLOCK-- A device that prevents an action from
taking place at the desired time, but will allow the
HORSEPOWER (hp)-- The English unit of power,
action when all required conditions are met.
equal to work done at the rate of 550 foot-pounds
ION-- An electrically charged atom or group of atoms.
per second. Equal to 746 watts of electrical power.
Negative ions have an excess of electrons; positive
HOT WIRE METER MOVEMENT-- A meter
ions have a deficiency of electrons.
movement that uses the expansion of a heated wire
JACKING GEAR-- Electric motor-driven device that
to move the pointer of a meter; measures ac or dc.
rotates the turbine shaft, reduction gears, and line
HYDRAULIC ACTUATOR-- A device that converts
shaft at a low speed.
hydraulic pressure to mechanical movement.
KILO-- A prefix meaning one thousand.
HYDROGEN BLISTERING-- The formation of
KINETIC ENERGY-- Energy that a body possesses
blisterlike bulges on or below the surface of a
by virtue of its motion.
ductile metal caused by excessive internal
hydrogen pressure. Hydrogen may be formed
KIRCHHOFF'S LAWS-- (1) The algebraic sum of
during cleaning, plating, corrosion, or cathodic
the currents flowing toward any point in an electric
network is zero. (2) The algebraic sum of the
products of the current and resistance in each of the
HYDROGEN EMBRITTLEMENT-- Severe loss of
conductors in any closed path in a network is equal
to the algebraic sum of the electromotive forces in
metal; for example, through pickling, cleaning, or
LEAD-ACID CELL-- A cell in an ordinary storage
HYDROMETER-- An instrument used to measure
battery, in which electrodes are grids of lead
specific gravity. In batteries, hydrometers are used
containing an active material consisting of certain
to indicate the state of charge by the specific gravity
lead oxides that change in composition during
of the electrolyte.
charging and discharging. The electrodes or plates
are immersed in an electrolyte of diluted sulfuric
a magnetic material behind the magnetizing force
producing it, caused by the molecular friction of the
molecules trying to align themselves with the
LINE OF FORCE-- A line in an electric or magnetic
magnetic force applied to the material.
field that shows the direction of the force.