MAGNETIC FIELDS BASICS
Glossary of Terms
Air gap
A low
permeability gap in the flux path of a magnetic circuit. Often
air, but inclusive of other materials such as paint, aluminum,
etc.
Amplification (of a magnetic field)
The process
by which fluid motions in a conducting fluid can make a weak
magnetic field become stronger. On the Sun, stretching of the
field
lines of a magnetic field, coupled with
field
line preservation, will amplify the field.
Angstrom
A unit of length equal to 0.00000001 centimeters. This may also
be written as 1 x 10-8 cm
Anisotropic
magnet
A magnet
having a preferred direction of magnetic orientation, so that
the magnetic characteristics are optimum in one preferred
direction
Aurora, polar
(also known north of the equator as northern lights or aurora
borealis ["northern dawn"], and south of it as aurora australis)
A glow seen
in the sky, usually in the
auroral zone,
caused by electrons hitting atmospheric atoms and causing them
to emit light. The typical aurora is produced at altitudes
around 100 km (60 miles), by
electrons
of 3-15,000
electron volts.
Most aurora is greenish, caused by light emitted from oxygen, or
red, also from oxygen. Electrons producing auroral arcs seen
from the ground have usually undergone acceleration in the
magnetosphere
by electric currents that connect Earth to space. Electrons
observed by satellite imagers, often as rings around the
auroral oval,
are usually escaping from the Earth's
magnetotail.
Their glow is too dim to be seen by eye from the ground.
Closed
circuit
This exists
when the flux path external to a permanent magnet is confined
within high permeability materials that compose the magnet
circuit.
Coercive
force, Hc
The
demagnetizing force, measured in Oersteds, necessary to reduce
observed induction, B, to zero after the magnet has previously
been brought to saturation.
Curie
temperature, Tc
The
temperature at which the parallel alignment of elementary
magnetic moments completely disappears, and the material is no
longer able to hold magnetization.
declination
(magnetic). The difference between magnetic north, given by the
compass needle, and true north, the horizontal projection of the
direction of the Earth axis.
demagnetization curve: The second quadrant of the hysteresis
loop, generally describing the behavior of magnetic
characteristics in actual use. Also known as the B-H Curve.
Dip angle
The local
angle between the horizontal and the direction of the magnetic
force. Indicated by a freely-floating magnetic needle, free to
turn to any direction in space, or by a "dip circle" instrument,
which has a needle pivoted around a horizontal axis aligned in
the magnetic east-west direction.
Dipole
a compact
source of magnetic force, with two magnetic
poles.
A bar magnet, coil or current loop, if their size is small,
create a dipole field. The Earth's field, as a crude
approximation, also
resembles that of a dipole,
located near the Earth's center.
Dynamo
Also known
as "generator," a machine creating electric currents by relative
motions between the conductors that carry them and magnets of
electromagnets. In geomagnetism the term is also used for
naturally occurring fluid flows through a magnetic field,
generating electric currents. A self-excited dynamo (of either
kind) is one in which the generated current creates the magnetic
field by which the dynamo operates.
Dynamo
process
The
generation of magnetic field by motions of a fluid that conducts
electricity, motions driven by some source of energy (e.g. heat
convection).
Dynamo theory
The theory
of fluid dynamos. Initially, "kinematic dynamo theory" asked
whether dynamo processes were at all possible, and after some
decades of study, the answer was "yes." "MHD
(magneto-hydrodynamic) dynamo theory" searches for dynamos which
also satisfy consistent pressure and force structures.
Dynamo,
fluid
A
dynamo
process occurring in a fluid that conducts electricity.
Eddy
currents
Circulating
electrical currents that are induced in electrically conductive
elements when exposed to changing magnetic fields, creating an
opposing force to the magnetic flux. Eddy currents can be
harnessed to perform useful work (such as damping of movement),
or may be unwanted consequences of certain designs, which should
be accounted for or minimized.
Electric
charge
A property
of
electrons
and
ions,
causing them to attract each other, and to repel particles of
the same kind. The electric charge of electrons is called
"negative" (-) and that of ions "positive" (+). Materials such
as glass, fur and cloth acquire an electric charge by rubbing
against each other, a process which tears electrons off one
substance and attaches it to the other. Electric charges (+) and
(-) may also be separated by a chemical process, as in an
electric battery.
Electric
current
a continuous
flow of electric charge through a material which conducts
electricity, carried by ions and/or electrons. Currents usually
flow in a closed circuit, without beginning or end. In daily
life a current is generally driven through wires by a voltage
("electric pressure") produced by batteries or generators. Some
currents in space plasmas are also produced this way, but many
are inherent to the way ions and electrons move through magnetic
fields, e.g. their drifts.
Electricity
Colloquially, electric charge and currents, viewed as a "fluid"
which may be attached to matter or flow through it. The word
came from "elektron," the Greek name of amber, one of the
materials which when dry and lightly rubbed can attract small
objects (by "static electricity"). The Greeks and Romans already
knew about such attractions, but William Gilbert, who
studied them,
called such materials "electricks," and from that came the
modern term.
Electromagnet
A magnet,
consisting of a solenoid with an iron core, which has a magnetic
field existing only during the time of current flow through the
coil.
Electromagnetic spectrum
The full range of
frequencies, from radio waves to gamma rays, that
characterizes light.
Electromagnetic waves (radiation)
Another term for light. Light waves are fluctuations of electric
and
magnetic
fields in space.
Electron
A negatively charged particle commonly found in the outer layers
of atoms. The electron has only 0.0005 the mass of the
proton.
ELF
Extremely
low frequency magnetic field
EMF
Electromagnetic field
Energy
product
Indicates
the energy that a magnetic material can supply to an external
magnetic circuit when operating at any point on its
demagnetization curve. Calculated as Bd x Hd,
and measured in Mega Gauss Oersteds, MGOe.
Ferromagnetic
A material
which like iron ("ferrum" in Latin) can become strongly
magnetized, temporarily or permanently. William Gilbert named
such materials "magneticks."
Ferromagnetic material
A material
whose permeability is very much larger than 1 (from 60 to
several thousand times 1), and which exhibits hysteresis
phenomena.
Field
The region
in which a particular type of force can be observed; depending
on the force, one can thus speak of a gravity field, magnetic
field, electric field (or when the two are linked by fast
oscillations, electromagnetic field) and nuclear field. The laws
of physics suggest that fields represent more than a possibility
of force being observed, and that they can also transmit energy
and momentum, e.g. a light wave is a phenomenon completely
defined by fields. For that reason a field is often viewed as a
space which was modified by the sources of the force which the
field represents.
Field,
electric
The region
in which electric forces can be observed, e.g. near an electric
charge.(see
field).
Field,
electromagnetic(EM field)
The regions
of space near electric currents, magnets, broadcasting antennas
etc., regions in which electric and magnetic forces may act (see
field).
Unchanging magnetic or electric phenomena can often be handled
by just considering the magnetic or the electric field alone;
however wave phenomena such as radio and light involve a tight
interplay of time-varying electric and magnetic fields, viewed
as manifestations of their
electromagnetic fields.
Field line,
closed
In
magnetospheric physics, field lines which are not open, but have
both ends attached to Earth. The field lines reaching most
locations on Earth are closed and can trap charged particles.
Field line,
open
In
magnetospheric physics, a field line whose one end reaches Earth
(specifically, the conducting ionosphere layer in the high
atmosphere) but whose other end extends into the solar wind.
Presumably, such lines have undergone
magnetic
reconnection. Because plasma and energy easily flow
along magnetic field lines, these lines offer an easy pathway by
which energy and plasma can flow from the solar wind to the
Earth's magnetosphere.
Field
line preservation
A predicted
property of fluids which are perfect conductors of electricity
(including "ideal plasmas"), fairly closely obeyed in much of
the space environment. By this property, two particles which
initially share the same field line, continue to do so into the
future, even if the line is deformed. The opposite also holds
for such fluids: two particles which start out on different
field lines will always be on different field lines (but see
magnetic
reconnection).
Field
lines, magnetic
Imaginary
lines in space used for visually representing magnetic fields
(just as lines of latitude and longitude are used to represent
locations on Earth). At any point in space, the local field line
points in the direction an ideal compass needle would assume, if
it were free to rotate in 3 dimensions. It is also the direction
of the magnetic force--the force which an isolated magnetic pole
at that point would experience. In a plasma, magnetic field
lines guide the motion of
ions
and
electrons,
are sometimes able to
trap them
and direct the flow of some electric currents.
Field,
magnetic
The region
where magnetic forces can be observed.
Flux
The
condition existing in a medium subjected to a magnetizing force.
This quantity is characterized by the fact that an electromotive
force is induced in a conductor surrounding the flux at any time
the flux changes in magnitude. The cgs unit of flux is the
Maxwell.
Fluxmeter
An
instrument that measures the change of flux linkage with a
search coil.
Frequency
A property of a wave that describes how many wave patterns or
cycles pass by in a period of time. Frequency is often measured
in
Hertz
(Hz), where a wave with a frequency of 1 Hz will pass by at 1
cycle per second.
Fringing
fields
Leakage flux
particularly associated with edge effects in a magnetic circuit.
Gamma ray
The highest energy, shortest
wavelength
electromagnetic radiations. Usually, they are thought
of as any
photons
having energies greater than about 100 keV. (It's "gamma-ray"
when used as an adjective.)
Gauss
Lines of
magnetic flux per square centimeter, cgs unit of flux density,
equivalent to lines per square inch in the English system, and
Webers per square meter or Tesla in the SI system.
Gaussmeter
An
instrument that measures the instantaneous value of magnetic
induction, B. Its principle of operation is usually based on one
of the following: the Hall effect, nuclear magnetic resonance (NMR),
or the rotating coil principle.
Hertz,
Heinrich (1857 - 1894)
A German
physics professor who did the first experiments with generating
and receiving
electromagnetic waves, in particular radio waves. In
his honor, the units associated with measuring the cycles per
second of the waves (or the number of times the tip-tops of the
waves pass a fixed point in space in 1 second of time) is called
the hertz.
Hertz; Hz
The derived
SI
unit of
frequency,
defined as a frequency of 1 cycle per
second.
Hysteresis
loop
A closed
curve obtained for a material by plotting corresponding values
of magnetic induction, B, (on the abscissa) against magnetizing
force, H, (on the ordinate).
Induction, B
The magnetic
flux per unit area of a section normal to
the direction of flux. Measured in Gauss, in the cgs system of
units.
Infrared
Electromagnetic radiation at
wavelengths longer than the red end of visible light
and shorter than microwaves (roughly between 1 and 100 microns).
Almost none of the infrared portion of the
electromagnetic spectrum can reach the surface of the
Earth, although some portions can be observed by high-altitude
aircraft (such as the Kuiper Observatory) or telescopes on high
mountaintops (such as the peak of Mauna Kea in Hawaii).
Intrinsic
coercive force, Hci
Measured in
Oersteds in the cgs system, this is a measure of the materialيs
inherent ability to resist demagnetization. It is the
demagnetization force corresponding to zero intrinsic induction
in the magnetic material after saturation. Practical
consequences of high Hci values are seen in greater temperature
stability for a given class of material, and greater stability
in dynamic operating conditions.
Intrinsic induction, Bi
The
contribution of the magnetic material to the total magnetic
induction, B. It is the vector difference between the magnetic
induction in the material and the magnetic induction that would
exist in a vacuum under the same field strength, H. This
relationship is expressed as: Bi = B-H.
Ions
An atom with one or more electrons stripped off, giving it a net
positive charge.
Irreversible
loss
Defined as
the partial demagnetization of a magnet caused by external
fields or other factors. These losses are only recoverable by
re-magnetization. Magnets can be stabilized to prevent the
variation of performance caused by irreversible losses.
Isotropic magnet
A magnet
material whose magnetic properties are the same in any
direction, and which can therefore be magnetized in any
direction without loss of magnetic characteristics.
Keeper
A piece of
soft iron that is placed on or between the poles of a magnet,
decreasing the reluctance of the air gap and thereby reducing
the flux leakage from the magnet.
Knee of the
demagnetization curve
The point at
which the B-H curve ceases to be linear. All magnet materials,
even if their second quadrant curves are straight line at room
temperature, develop a knee at some temperature. Alnico 5
exhibits a knee at room temperature. If the operating point of a
magnet falls below the knee, small changes in H produce large
changes in B, and the magnet will not be able to recover its
original flux output without re-magnetization.
Laser
Laser is an acronym for Light Amplification by Stimulated
Emission of Radiation. It's a device that produces a coherent
beam of optical radiation by stimulating electronic, ionic, or
molecular transitions to higher levels so that when they return
to lower energy levels they emit energy.
Leakage flux
That portion
of the magnetic flux that is lost through leakage in the
magnetic circuit due to saturation or air-gaps, and is therefore
unable to be used.
Length of air-gap, Lg
The length
of the path of the central flux line in the air-gap.
Light
The common term for
electromagnetic radiation, usually referring to that
portion visible to the human eye. However, other bands of the
e-m
spectrum
are also often referred to as different forms of light.
Line of
force
Michael
Faraday's original term for what is now known as
magnetic field line.
Load line
A line drawn
from the origin of the Demagnetization Curve with a slope of
-B/H, the intersection of which with the B-H curve represents
the operating point of the magnet. Also see Permeance
Coefficient.
Lodestone
(also spelled loadstone)
A rare
mineral, found to have strong permanent magnetization. For many
centuries, lodestones provided humanity with its only known
source of magnetism. The mineral is a rare form of fine-grained
magnetite and is believed to acquire its magnetic properties
when struck by lightning.
Magnetic
circuit
An assembly
consisting of some or all of the following: permanent magnets,
ferromagnetic conduction elements, air gaps, electrical
currents.
Magnetic
field
A description of the strength of the magnetic force exerted by
an object. Bar magnets have "di-polar" fields, as the force is
exerted from the two ends of the bar. In simple terms, the
earth, the sun, stars,
pulsars
all have dipolar magnetic fields.
Magnetic
flux
The total
magnetic induction over a given area. When the magnetic
induction, B, is uniformly distributed over an area A, Magnetic
Flux = BA.
Magnetizing
force, H
The
magnetomotive force per unit length at any point in a magnetic
circuit. Measured in Oersteds in the cgs system.
Magnetomotive force, F
Analogous to
voltage in electrical circuits, this is the magnetic potential
difference between any two points.
Magnetic
induction
This term
may refer to one of two phenomena, either
induced magnetism
or electromagnetic induction. The latter may be loosely defined
as the ability of a substance that conducts electricity to
develop a circulating current, if it senses a changing magnetic
field. The change might come either from of variation of the
strength of the magnetic source, or from the motion of the
conductor relative to that source. The dynamo process is based
on such currents.
Magnetic
pole
(1)A
magnetic pole of a bar magnet is a compact source of magnetic
force near the end of the bar. Magnetic poles always come in
matched pairs, north-seeking (N) and south-seeking (S). Magnetic
poles are just an observed consequence of the way magnetic field
lines are channeled by the bar: actually, the bar's
magnetization is evenly spread inside it and is not concentrated
at its ends. (2) The magnetic pole of Earth is one of the two
points on Earth towards which the compass needle seems to point.
At the pole, the magnetic force is vertical. The magnetic poles
of Earth are near the geographic poles, the points where the
Earth's surface intersects its rotation axis; however the two
are not the same, and on Uranus and Neptune
are quite widely separated.
Magnetic
(scalar) potential
The magnetic
force at a point in space is a
"vector"
quantity, one which has both direction and strength. To specify
it, three numbers are required--for instance, one specifying its
strength and two its direction. However, the magnetic field near
the surface of the Earth (and at any other location where
electric currents are absent) is of a relatively simple kind,
describable by a single varying quantity--an ordinary number or
"scalar", as distinct from a vector. A similar simplified
representation exists for the force of gravity, even when its
sources are complicated. The magnetic scalar potential was
introduced for describing the Earth's magnetic field by
Gauss
and is described in terms of "spherical
harmonics."
It is still being used.
Magnetization, induced
The
magnetization of iron and similar
"ferromagnetic"
materials, when placed near a magnet or lodestone. In
magnetically
"soft"
materials this magnetization is only temporary.
Magnetize
Cause to
become magnetic. This can happen by placing the material in the
strong magnetic field produced by a permanent magnet or by an
electric current, or when heated material which can become
magnetic (e.g. iron or basaltic lava) cools down in the presence
of a magnetic field.
Magnetometer
An
instrument for measuring the direction and/or intensity of
magnetic fields.
Spacecraft often carry fluxgate magnetometers, which measure
components of the magnetic field (3 of them are combined to
provide all three, giving both strength and direction of the
field) but they need to be calibrated. Instruments using
rubidium vapor measure only the field strength, but their
reading is absolute, related to atomic constants.
Magnetometer, fluxgate
An
electronic magnetometer based on the saturation of certain
magnetizable materials. Can be made very sensitive.
Magnetometer,
proton precession
An
electronic magnetometer based on the resonance between protons
(hydrogen nuclei) and an oscillating electromagnetic signal.
Protons are small magnets, and the magnetic strength of each
(like the proton's mass) always has the same value, which is
well known. Because of this, the resonance frequency has a
simple relation to the strength of the magnetic field. By
measuring that frequency, the magnetic field strength can be
immediately calculated, and no calibration of the instrument is
needed.
Magnetometer, Overhauser effect
A greatly
improved version of the proton precession magnetometer
(preceding item), using an added chemical to enhance
performance.
Magnetometer, alkali vapor
A
magnetometer which, like the proton precession type, is based on
an atomic resonance process and therefore requires no
calibration. A glass chamber containing the vapor of an alkali
metal (e.g. rubidium or caesium) becomes slightly more opaque to
a specific light frequency when exposed to a radio signal of
resonant frequency. That frequency gives the strength of the
surrounding magnetic field.
Magnetopause
The boundary
of the magnetosphere, separating plasma attached to Earth from
that of the flowing solar wind.
Magnetosphere
The region of space in which the
magnetic
field of an object (e.g., a star or planet)
dominates the radiation pressure of the
stellar
wind to which it is exposed.
Magnetotail
The portion of a planetary
magnetosphere which is pushed in the direction of the
solar wind.
Main field
(of Earth)
A term
frequently used by scientists for the internal magnetic field of
the Earth, in distinction from fields originating outside its
surface.
Maximum
energy product, BHmax
The point on
the Demagnetization Curve where the product of B and H is a
maximum and the required volume of magnet material required to
project a given energy into its surroundings is a minimum.
Measured in Mega Gauss Oersteds, MGOe.
Meter; m
The fundamental
SI
unit of length, defined as the length of the path traveled by
light in vacuum during a period of 1/299 792 458 s. A unit of
length equal to about 39 inches. A kilometer is equal to 1000
meters.
MF
Magnetic
field
Microwave
Electromagnetic radiation which has a longer
wavelength (between 1 mm and 30 cm) than visible
light. Microwaves can be used to study the Universe, communicate
with satellites in Earth orbit, and cook popcorn.
MHD
Short for
"magneto-hydrodynamics, " the theory of fluids which conduct
electricity. MHD is applicable to the Earth's fluid core and
also to many
plasmas.
MHD dynamo theory
The theory
of dynamo action in conducting fluids, including force balance
and other physical effects.
MRI
Magnetic
resonance imaging
Noise
The random fluctuations that are always associated with a
measurement that is repeated many times over.
North pole
That pole of
a magnet which, when freely suspended, would point to the north
magnetic pole of the earth. The definition of polarity can be a
confusing issue, and it is often best to clarify by using "north
seeking pole" instead of "north pole" in specifications.
North
seeking pole
The
pole of a bar magnet
which, if the magnet is freely suspended (or is placed on a
"boat" floating on water) tends to point northward. Also known
as the "north pole" (or "N pole") of the bar magnet. However, it
should be noted that if a bar magnet at the center of the Earth
were the source of the Earth's field, the N-pole of that bar
would be directed southward, because it tends to repel another
N-pole, not attract it.
Oersted, Oe
A cgs unit
of measure used to describe magnetizing force. The English
system equivalent is Ampere Turns per Inch, and the SI systemيs
is Ampere Turns per Meter.
Orientation direction
The
direction in which an anisotropic magnet should be magnetized in
order to achieve optimum magnetic properties. Also known as the
"axis", "easy axis", or "angle of inclination".
Paramagnetic
material
A material
having a permeability slightly greater than 1.
PEMF
Pulsed
electromagnetic field
permeance
The inverse
of reluctance, analogous to conductance in electrical circuits.
Permeance coefficient, Pc
Ratio of the
magnetic induction, Bd, to its self demagnetizing force, Hd. Pc
= Bd / Hd. This is also known as the "load line", "slope of the
operating line", or operating point of the magnet, and is useful
in estimating the flux output of the magnet in various
conditions. As a first order approximation, Bd / Hd = Lm/Lg,
where Lm is the length of the magnet, and Lg is the length of an
air gap that the magnet is subjected to. Pc is therefore a
function of the geometry of the magnetic circuit.
Photon
The smallest (quantum) unit of light/electromagnetic energy.
Photons are generally regarded as particles with zero mass and
no electric charge.
Plasma
A gas
containing free
ions
and
electrons,
and therefore capable of conducting electric currents. A
"partially ionized plasma" such as the Earth's ionosphere or the
gas inside a fluorescent lamp is one that also contains neutral
atoms.
Plasma sheet
The region
in the
magnetotail
of relatively denser plasma and rather weak magnetic field,
stretching tailwards from the Earth's magnetic equator. It
separates the two
tail lobes
and is the site of
substorms
and the source region of most of the
polar aurora.
Polarization
A
special property of light; light has three properties,
brightness, color and polarization. Polarization is a condition
in which the planes of vibration of the various rays in a light
beam are at least partially aligned.
Pole pieces
Ferromagnetic materials placed on magnetic poles used to shape
and alter the effect of lines of
flux.
Positron
The antiparticle to the
electron.
The positron has most of the same characteristics as an electron
except it is positively charged.
Proton
A particle with a positive charge commonly found in the nucleus
of atoms.
Radiation
belt
Regions of charged particles in a
magnetosphere.
Radio
Electromagnetic radiation which has the lowest
frequency,
the longest
wavelength, and is produced by charged particles
moving back and forth; the atmosphere of the Earth is
transparent to radio waves with wavelengths from a few
millimeters to about twenty meters.
Relative
permeability
The ratio of
permeability of a medium to that of a vacuum. In the
cgs system, the permeability is equal to 1 in a vacuum by
definition. The permeability of air is also for all practical
purposes equal to 1 in the cgs system.
Reluctance,
R
Analogous to
resistance in an electrical circuit, reluctance is related to
the magnetomotive force, F, and the magnetic flux by the
equation R = F/(Magnetic Flux), paralleling Ohm's Law where F is
the magnetomotive force (in cgs units).
Remanence, Bd
The magnetic
induction that remains in a magnetic circuit after the removal
of an applied magnetizing force. If there is an air gap in the
circuit, the remanence will be less than the residual induction,
Br.
Residual induction, Br
This is the
point at which the hysteresis loop crosses the B axis at zero
magnetizing force, and represents the maximum flux output from
the given magnet material. By definition, this point occurs at
zero air gap, and therefore cannot be seen in practical use of
magnet materials.
Return path
Conduction
elements in a magnetic circuit which provide a low reluctance
path for the magnetic flux.
Reversals, magnetic
Episodes of
changes in the Earth's magnetic field which result in the
polarity of the north and south magnetic poles being
interchanged. Reversals have occurred in the geological history
of the Earth at typical intervals of 500,000 years. The Sun's
global magnetic polarity seems to reverse every 11-year sunspot
cycle.
Reversible
temperature coefficient
A measure of
the reversible changes in flux caused by temperature variations.
Saturation
The
condition under which all elementary magnetic moments have
become oriented in one direction. A ferromagnetic material is
saturated when an increase in the applied magnetizing force
produces no increase in induction. Saturation flux densities for
steels are in the range of 16,000 to 20,000 Gauss.
Scientific
notation
A compact format for writing very large or very small numbers,
most often used in scientific fields. The notation separates a
number into two parts: a decimal fraction, usually between 1 and
10, and a power of ten. Thus 1.23 x 104 means 1.23
times 10 to the fourth power or 12,300; 5.67 x 10-8
means 5.67 divided by 10 to the eighth power or 0.0000000567.
Search coil
A coil
conductor, usually of known area and number of turns that is
used with a fluxmeter to measure the change of flux linkage with
the coil.
SMF
Static
magnetic field
Soft
materials (magnetically)
Materials
such as soft iron which become temporary magnets when placed
near permanent magnets or electric currents, but lose their
magnetization when taken away again.
South
seeking pole
The magnetic
pole (for example, on a bar magnet) which, when freely suspended
in space, tends to point south. See
north-seeking pole.
Stabilization
Exposure of
a magnet to demagnetizing influences expected to be encountered
in use in order to prevent irreversible losses during actual
operation. Demagnetizing influences can be caused by high or low
temperatures, or by external magnetic fields.
Synchrotron
radiation
Electromagnetic radiation given off when very high
energy electrons encounter
magnetic
fields.
TMF
Time-varied
magnetic field
Toroidal
field
One of two
modes of magnetic fields (particularly in spherical
configurations), the other being the
poloidal field.
A typical toroidal field is the one created by a current in a
long straight wire, with ring-shaped ("torus shaped") field
lines around the wire. A general magnetic field has a toroidal
part and a poloidal part. On the Sun, the uneven solar rotation
(faster near the equator) amplifies only the toroidal part,
though the poloidal field is essential to the process.
TVF
Time-varied
magnetic field
Temperature
coefficient
A factor,
which describes the change in a magnetic property with change in
temperature. Expressed as percent change per unit of
temperature.
Ultraviolet
Electromagnetic radiation at
wavelengths shorter than the violet end of visible
light; the atmosphere of the Earth effectively blocks the
transmission of most ultraviolet light.
Visible
Electromagnetic radiation at
wavelengths which the human eye can see. We perceive
this radiation as colors ranging from red (longer wavelengths; ~
700 nanometers) to violet (shorter wavelengths; ~400
nanometers.)
Wave-particle duality
The principle of quantum mechanics which implies that light
(and, indeed, all other subatomic particles) sometimes act like
a wave, and sometimes act like a particle, depending on the
experiment you are performing. For instance, low
frequency
electromagnetic radiation tends to act more like a
wave than a particle; high frequency electromagnetic radiation
tends to act more like a particle than a wave.
Wavelength
The distance between adjacent peaks in a series of periodic
waves. Also see
electromagnetic spectrum.
Weber
The
practical unit of magnetic flux. It is the amount of magnetic
flux which, when linked at a uniform rate with a single-turn
electric circuit during an interval of 1 second, will induce in
this circuit an electromotive force of 1 volt.
X-ray
Electromagnetic radiation of very short
wavelength and very high-energy; X-rays have shorter
wavelengths than ultraviolet light but longer wavelengths than
gamma rays.
