18WuD2x

430 magnetic wire • magnetostriction
magnetic wire The thin wire used in wire recording
and playback. See WIRE RECORDER.
magnetism The property of having or causing a
magnetic field. It occurs when magnetic dipoles
are aligned and when electric charge carriers are
in motion.
magnetite A natural magnetic oxide of iron. Also
called LODESTONE.
magnetization curve A curve depicting the magnetization
of a material versus the applied magnetizing
force. See, for example, HYSTERESIS
CURVE.
magnetizer A device for magnetizing magnetic materials,
as in the making of permanent magnets.
Also see MAGNET CHARGER. Compare DEMAG-
NETIZER.
magnetizing current 1. A current that sets up a
magnetic field of useful intensity. 2. The halfcycle
of an alternating current or the polarity of a
direct current flowing through a coil wound on a
permanent magnet (as in a headphone, permanent-magnet
loudspeaker, or polarized relay) that
increases magnetic field strength. Compare DE-
MAGNETIZING CURRENT. 3. The field current of
a dynamo.
magnetizing force 1. Magnetomotive force (in
gilberts) divided by spatial distance (in meters). 2.
The intensity of a magnetic field that causes a
material to become magnetized.
magnet keeper See KEEPER.
magnet meter See MAGNET TESTER.
magnet motor See PERMANENT-MAGNET MOTOR.
magneto See PERMANENT-MAGNET GENERATOR.
magnetocardiogram Abbreviation, MCG. A record,
made by a MAGNETOCARDIOGRAPH, of the pulsating
magnetic field of the heart. It is used as a
diagnostic aid.
magnetocardiograph An instrument that produces
a record of the pulsating magnetic field
generated around the torso by natural ion currents
in the heart.
magnetoelectric generator See MAGNETOGEN-
ERATOR.
magnetofluid mechanics See MAGNETOHYDRO-
DYNAMICS.
magnetofluidynamics See MAGNETOHYDRODY-
NAMICS.
magnetogasdynamics See MAGNETOHYDRODY-
NAMICS.
magnetoionic duct A propagation path for radio
waves between two points that have the same
geomagnetic longitude on the surface of the
earth. The radio waves tend to travel with the geomagnetic
lines of flux at some frequencies under
certain conditions.
magnetoionics The study of the effects of the geomagnetic
field on the propagation of radio waves.
magnetogenerator See PERMANENT-MAGNET
GENERATOR.
magnetograph An instrument for automatically
recording a magnetic field.
magnetohydrodynamic generator A device using
magnetohydrodynamic principles to generate
electric power directly from gases. In the generator,
a hot gas is passed through an intense magnetic
field; a pair of collector plates picks up
electrons from the ionized gas.
magnetohydrodynamic gyroscope A gyroscope
whose spin is obtained by a rotating magnetic
field circulating a conducting fluid, such as mercury,
around a closed loop. Also see MAGNETO-
HYDRODYNAMICS.
magnetohydrodynamic power generator See
MAGNETOHYDRODYNAMIC GENERATOR.
magnetohydrodynamics Abbreviation, MHD. The
theory and application of phenomena produced
by electrically conductive fluids and gases in electric
and magnetic fields.
magnetometer An instrument for measuring the
strength and direction of magnetic fields.
magnetomotive force Abbreviation, mmf. Unit,
ampere. The phenomenon that is sometimes descriptively
called magnetic pressure. It is analogous
to electromotive force (and to water
pressure) and is the agent that produces a magnetic
field.
magneton See BOHR MAGNETON.
magneto-optical rotation The tendency of a magnetic
field to rotate the plane of polarization of
light passing through a substance. Also see
KERR MAGNETO-OPTICAL EFFECT.
magneto-optical technology A computer datastorage
technology that uses lasers to guide the
read/write head in a magnetic disk drive. This
greatly increases the amount of data that can be
effectively stored on, and retrieved from, a magnetic
disk.
magneto-optical valve See KERR MAGNETO-
OPTICAL EFFECT.
magnetopause The high-altitude limit of the MAG-
NETOSPHERE.
magnetoplasmadynamics See MAGNETOHYDRO-
DYNAMICS.
magnetoresistance The phenomenon whereby the
resistance of a material, such as a semiconductor,
changes when it is exposed to a magnetic
field. Also see MAGNETORESISTOR.
magnetoresistor A material (such as bismuth
wire, indium antimonide, or indium arsenide)
whose resistance varies with the strength of a
magnetic field in which it is placed.
magnetosphere In the upper atmosphere, a region
extending thousands of kilometers from the
earth, in which charged particles are trapped by
the earth’s magnetic field.
magnetostatic field A stationary magnetic field,
such as that produced by a permanent magnet.
magnetostriction The expansion or contraction of
a bar or rod of magnetic material (such as Invar,
Monel metal, Nichrome, nickel, or Stoic metal) in
proportion to the strength of an applied magnetic
field. Magnetostrictive vibration in such a rod is