France Avčin.
Definition
A particle, carrying a charge of one
coulomb (C), and moving perpendicularly through a magnetic field of one tesla, at a speed of one metre per second (m/s), experiences a force with magnitude one
newton (N), according to the
Lorentz force law. That is,
:
As an
SI derived unit, the tesla can also be expressed in terms of other units. For example, a
magnetic flux of 1
weber (Wb) through a surface of one square meter is equal to a
magnetic flux density
A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and to ...
of 1 tesla.
[''The International System of Units (SI), 8th edition'', BIPM, eds. (2006), ]
Table 3. Coherent derived units in the SI with special names and symbols
That is,
:
Expressed only in
SI base units, 1 tesla is:
:
where A =
ampere, kg =
kilogram, and s =
second.
Additional equivalences result from the derivation of coulombs from
amperes (A),
:
:
the relationship between newtons and
joule
The joule ( , ; symbol: J) is the unit of energy in the International System of Units (SI). It is equal to the amount of work done when a force of 1 newton displaces a mass through a distance of 1 metre in the direction of the force applie ...
s (J),
:
:
and the derivation of the weber from
volt
The volt (symbol: V) is the unit of electric potential, electric potential difference (voltage), and electromotive force in the International System of Units (SI). It is named after the Italian physicist Alessandro Volta (1745–1827).
Defin ...
s (V),
:
:
Electric vs. magnetic field
In the production of the
Lorentz force, the difference between electric fields and magnetic fields is that a force from a
magnetic field on a charged particle is generally due to the charged particle's movement, while the force imparted by an electric field on a charged particle is not due to the charged particle's movement. This may be appreciated by looking at the units for each. The unit of
electric field in the
MKS system of units
The MKS system of units is a physical system of measurement that uses the metre, kilogram, and second (MKS) as base units. It forms the base of the International System of Units (SI), though SI has since been redefined by different fundamental ...
is newtons per coulomb, N/C, while the magnetic field (in teslas) can be written as N/(C⋅m/s). The dividing factor between the two types of field is metres per second (m/s), which is velocity. This relationship immediately highlights the fact that whether a static
electromagnetic field is seen as purely magnetic, or purely electric, or some combination of these, is dependent upon one's
reference frame
In physics and astronomy, a frame of reference (or reference frame) is an abstract coordinate system whose origin, orientation, and scale are specified by a set of reference points― geometric points whose position is identified both mathe ...
(that is, one's velocity relative to the field).
In
ferromagnets
Ferromagnetism is a property of certain materials (such as iron) which results in a large observed magnetic permeability, and in many cases a large magnetic coercivity allowing the material to form a permanent magnet. Ferromagnetic materials ...
, the movement creating the magnetic field is the
electron spin
In atomic physics, the electron magnetic moment, or more specifically the electron magnetic dipole moment, is the magnetic moment of an electron resulting from its intrinsic properties of spin and electric charge. The value of the electron magnet ...
(and to a lesser extent electron
orbital angular momentum). In a current-carrying wire (
electromagnet
An electromagnet is a type of magnet in which the magnetic field is produced by an electric current. Electromagnets usually consist of wire wound into a coil. A current through the wire creates a magnetic field which is concentrated in ...
s) the movement is due to electrons moving through the wire (whether the wire is straight or circular).
Conversion no non-SI units
One tesla is equivalent to:
: 10,000 (or 10
4) G (
gauss
Johann Carl Friedrich Gauss (; german: Gauß ; la, Carolus Fridericus Gauss; 30 April 177723 February 1855) was a German mathematician and physicist who made significant contributions to many fields in mathematics and science. Sometimes refer ...
), used in the
CGS system. Thus, 1 G = 10
−4 T = 100 μT (microtesla).
: 1,000,000,000 (or 10
9) γ (gamma), used in
geophysics
Geophysics () is a subject of natural science concerned with the physical processes and physical properties of the Earth and its surrounding space environment, and the use of quantitative methods for their analysis. The term ''geophysics'' so ...
.
Thus, 1 γ = 1 nT (nanotesla).
For the relation to the units of the
magnetising field (ampere per metre or
Oersted
The oersted (symbol Oe) is the coherent derived unit of the auxiliary magnetic field H in the centimetre–gram–second system of units (CGS). It is equivalent to 1 dyne per maxwell.
Difference between CGS and SI systems
In the CGS system, ...
), see the article on
permeability.
Examples
The following examples are listed in the ascending order of the magnetic-field strength.
* 3.2 × 10
−5 T (31.869 μT) – strength of
Earth's magnetic field
Earth's magnetic field, also known as the geomagnetic field, is the magnetic field that extends from Earth's interior out into space, where it interacts with the solar wind, a stream of charged particles emanating from the Sun. The magnetic ...
at 0° latitude, 0° longitude
* 4 × 10
−5 T (40 μT) – walking under a
high-voltage power line
* 5 × 10
−3 T (5 mT) – the strength of a typical
refrigerator magnet
A refrigerator magnet or fridge magnet is a small magnet, often attached to an artistic or whimsical ornament, which may be used to post items such as shopping lists, Christmas cards, child art or reminders on a refrigerator door, or which sim ...
* 0.3 T – the strength of solar sunspots
* 1.25 T – magnetic flux density at the surface of a
neodymium magnet
* 1 T to 2.4 T – coil gap of a typical loudspeaker magnet
* 1.5 T to 3 T – strength of medical
magnetic resonance imaging systems in practice, experimentally up to 17 T
* 4 T – strength of the
superconducting
Superconductivity is a set of physical properties observed in certain materials where electrical resistance vanishes and magnetic flux fields are expelled from the material. Any material exhibiting these properties is a superconductor. Unlike ...
magnet built around the
CMS
CMS may refer to:
Computing
* Call management system
* CMS-2 (programming language), used by the United States Navy
* Code Morphing Software, a technology used by Transmeta
* Collection management system for a museum collection
* Color manag ...
detector at
CERN
* 5.16 T – the strength of a specially designed room temperature
Halbach array
A Halbach array is a special arrangement of permanent magnets that augments the magnetic field on one side of the array while cancelling the field to near zero on the other side. This is achieved by having a spatially rotating pattern of magn ...
* 8 T – the strength of
LHC magnets
* 11.75 T – the strength of INUMAC magnets, largest
MRI scanner
The physics of magnetic resonance imaging (MRI) concerns fundamental physical considerations of MRI techniques and technological aspects of MRI devices. MRI is a medical imaging technique mostly used in radiology and nuclear medicine in order ...
* 13 T – strength of the superconducting
ITER magnet system
* 14.5 T – highest magnetic field strength ever recorded for an accelerator steering magnet at
Fermilab
Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a United States Department of Energy national laboratory specializing in high-energy particle physics. Since 2007, Fermilab has been opera ...
* 16 T – magnetic field strength required to levitate a
frog
A frog is any member of a diverse and largely carnivorous group of short-bodied, tailless amphibians composing the order Anura (ανοὐρά, literally ''without tail'' in Ancient Greek). The oldest fossil "proto-frog" ''Triadobatrachus'' is ...
(by
diamagnetic levitation of the water in its body tissues) according to the 2000
Ig Nobel Prize
The Ig Nobel Prize ( ) is a satiric prize awarded annually since 1991 to celebrate ten unusual or trivial achievements in scientific research. Its aim is to "honor achievements that first make people laugh, and then make them think." The name o ...
in Physics
* 17.6 T – strongest field trapped in a superconductor in a lab as of July 2014
* 27 T – maximal field strengths of
superconducting electromagnets at cryogenic temperatures
* 35.4 T – the current (2009) world record for a superconducting electromagnet in a background magnetic field
* 45 T – the current (2015) world record for continuous field magnets
* 97.4 T – strongest magnetic field produced by a "non-destructive" magnet
* 100 T – approximate magnetic field strength of a typical
white dwarf
A white dwarf is a stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very dense: its mass is comparable to the Sun's, while its volume is comparable to the Earth's. A white dwarf's faint luminosity comes ...
star
* 1200 T – the field, lasting for about 100 microseconds, formed using the electromagnetic flux-compression technique
[''D. Nakamura, A. Ikeda, H. Sawabe, Y. H. Matsuda, and S. Takeyama (2018)'']
Magnetic field milestone
/ref>
* 109 T – Schwinger limit
In quantum electrodynamics (QED), the Schwinger limit is a scale above which the electromagnetic field is expected to become nonlinear. The limit was first derived in one of QED's earliest theoretical successes by Fritz Sauter in 1931 and discu ...
above which the electromagnetic field itself is expected to become nonlinear
* 108 – 1011 T (100 MT – 100 GT) – magnetic strength range of magnetar
A magnetar is a type of neutron star with an extremely powerful magnetic field (∼109 to 1011 T, ∼1013 to 1015 G). The magnetic-field decay powers the emission of high-energy electromagnetic radiation, particularly X-rays and gamma rays.War ...
neutron stars
Notes and references
External links
Gauss ↔ Tesla Conversion Tool
{{DEFAULTSORT:Tesla (Unit)
SI derived units
Units of magnetic flux density
1960 introductions
Nikola Tesla