SI unit of magnetic field strength

The tesla (symbol: T) is a derived unit of the magnetic B-field strength (also, magnetic flux density) in the International System of Units.

One tesla is equal to one weber per square metre. The unit was announced during the General Conference on Weights and Measures in 1960 and is named[1] in honour of Serbian-American electrical and mechanical engineer Nikola Tesla, upon the proposal of the Slovenian electrical engineer France Avin.

The strongest fields encountered from permanent magnets on Earth are from Halbach spheres and can be over 4.5T. The record for the highest sustained pulsed magnetic field has been produced by scientists at the Los Alamos National Laboratory campus of the National High Magnetic Field Laboratory, the world's first 100-tesla non-destructive magnetic field.[2] In September 2018, researchers at the University of Tokyo generated a field of 1200T which lasted in the order of 100 microseconds using the electromagnetic flux-compression technique.[3]

A particle, carrying a charge of one coulomb, and moving perpendicularly through a magnetic field of one tesla, at a speed of one metre per second, experiences a force with magnitude one newton, according to the Lorentz force law. As an SI derived unit, the tesla can also be expressed as

(The last equivalent is in SI base units).[4]

Where A = ampere, C = coulomb, kg = kilogram, m = metre, N = newton, s = second, H = henry, V = volt, J = joule, and Wb = weber

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,[5] 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 is newtons per coulomb, N/C, while the magnetic field (in teslas) can be written as N/(Cm/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 (that is, one's velocity relative to the field).[6][7]

In ferromagnets, the movement creating the magnetic field is the electron spin[8] (and to a lesser extent electron orbital angular momentum). In a current-carrying wire (electromagnets) the movement is due to electrons moving through the wire (whether the wire is straight or circular).

One tesla is equivalent to:[9][pageneeded]

One tesla is equal to 1 Vs/m2. This can be shown by starting with the speed of light in vacuum,[11] c = (00)1/2, and inserting the SI values and units for c (2.998108m/s), the vacuum permittivity 0 (8.851012As/(Vm)), and the vacuum permeability 0 (12.566107Tm/A). Cancellation of numbers and units then produces this relation.

For the relation to the units of the magnetising field (ampere per metre or Oersted), see the article on permeability.

The following examples are listed in ascending order of field strength.

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Tesla (unit) - Wikipedia