# Tesla (unit)

Tesla (unit)

The tesla (symbol T) is the SI derived unit of magnetic field B (which is also known as "magnetic flux density"). One tesla is equal to one weber per square meter, and it was defined in 1960[1] in honour of the inventor, physicist, and electrical engineer Nikola Tesla. The strongest fields encountered from permanent magnets are from Halbach spheres which can be over 5 T.[2]

## Definition

This SI unit is named after Nikola Tesla. As with every SI unit whose name is derived from the proper name of a person, the first letter of its symbol is upper case (T). When an SI unit is spelled out in English, it should always begin with a lower case letter (tesla), except where any word would be capitalized, such as at the beginning of a sentence or in capitalized material such as a title. Note that "degree Celsius" conforms to this rule because the "d" is lowercase. —Based on The International System of Units, section 5.2.

A particle carrying a charge of 1 coulomb and passing through a magnetic field of 1 tesla at a speed of 1 meter per second perpendicular to said field experiences a force of 1 newton, according to the Lorentz force law. As an SI derived unit, the tesla can also be expressed as

$\mathrm{1\, T = 1\,\frac{V\cdot s}{m^2} = 1\,\frac{N}{A\cdot m} = 1\,\frac{Wb}{m^2} = 1\,\frac{kg}{C\cdot s} = 1\,\frac{kg}{A\cdot s^2} = 1\,\frac{N\cdot s}{C\cdot m}}$

(in SI base units).[3]

Units used:

A = ampere
C = coulomb
kg = kilogram
m = meter
N = newton
s = second
T = tesla
V = volt
Wb = weber

## Electric vs Magnetic Field

The difference between magnetic field strength (in tesla) vs electric field strength can be confusing.[citation needed]

The difference is that a force of magnetic field on a charged particle is generally due to the charged particle's movement[4] while the force imparted by an electric field on a charged particle is not due to the charged particle's movement. This can be seen by looking at the units for each. Electric field is N/C, while magnetic field (in tesla) can be written as N/(C*m/s). The difference between the two is m/s, or velocity. This can further be seen by noting that whether a field is magnetic or electric is dependent on one's relativistic reference frame (that is: one's velocity relative to the field).[5][6]

In ferromagnets the movement creating the magnetic field is the electron spin[7] (and to a lesser extent electron orbital angular momentum). In current carrying wire (electromagnets) the movement is due to electrons moving through the wire (whether the wire's straight or circular).

## History

The tesla was announced in honor of the Serbian inventor and electrical engineer Nikola Tesla, during the Conférence Générale des Poids et Mesures in 1960.

## Conversions

1 tesla is equivalent to:

10,000 (or 104) G (gauss), used in the CGS system. Thus, 10 G = 1 mT (millitesla), and 1 G = 10−4 T.
1,000,000,000 (or 109) γ (gammas), used in geophysics. Thus, 1 γ = 1 nT (nanotesla)

For those concerned with low-frequency electromagnetic radiation in the home, the following conversions are needed most:

1000 nT (nanotesla) = 1 µT (microtesla) = 10 mG (milligauss)
1,000,000 µT = 1 T

Because the tesla is so large in regards to everyday usage, common engineering practice is to report the strength of magnets in Gauss. Scientists are split on this issue, with some insisting on proper SI units at all times and some allowing for more practical labeling.

For the relation to the units of the magnetizing field (amperes per meter or oersteds) see the article on permeability.

## Examples

• 31 µT (3.1×10−5 T) - strength of Earth's magnetic field at 0° latitude (on the equator)
• 5 mT - the strength of a typical refrigerator magnet
• 1.25 T - magnetic field intensity 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[8]

## References

1. ^ "Details of SI units". sizes.com. 2011-07-01. Retrieved 2011-10-04.
2. ^ "...our data of 5.16 T dipole magnet...", The Strongest Permanent Dipole Magnet
3. ^ The International System of Units (SI), 8th edition, BIPM, eds. (2006), ISBN 92-822-2213-6, Table 3. Coherent derived units in the SI with special names and symbols
4. ^ Gregory, Frederick (2003). History of Science 1700 to Present. The Teaching Company.
5. ^ Parker, Eugene (2007). Conversations on electric and magnetic fields in the cosmos. Princeton University press. p. 65.
6. ^
7. ^ Herman, Stephen (2003). Delmar's standard textbook of electricity. Delmar Publishers. p. 97.
8. ^ "Ultra-High Field". Bruker BioSpin. Retrieved 2011-10-04.

Wikimedia Foundation. 2010.

### Look at other dictionaries:

• Tesla — may refer to:In science* Nikola Tesla (1856 – 1943), a Serbian American physicist, inventor, and electrical engineer * Tesla (unit) (symbol T), SI derived unit of magnetic flux density (or magnetic inductivity), named after Nikola Tesla * TESLA,… …   Wikipedia

• Tesla (unite) — Tesla (unité) Pour les articles homonymes, voir Tesla …   Wikipédia en Français

• tesla — /tes leuh/, n. a unit of magnetic induction equal to one weber per square meter. Abbr.: T [named after N. TESLA] * * * ▪ unit of energy measurement       unit of magnetic induction or magnetic flux density in the metre–kilogram–second system (SI) …   Universalium

• Tesla coil — at Questacon the National Science and Technology center in Canberra, Australia Uses Application in educational demonstrations, novelty lighting, as well as music Inventor …   Wikipedia

• tesla — 1960, unit of magnetic flux density, from Nikola Tesla (1856 1943), Croatian born U.S. engineer. Tesla coil is attested from 1896 …   Etymology dictionary

• tesla — ► NOUN Physics ▪ the SI unit of magnetic flux density. ORIGIN named after the American electrical engineer Nikola Tesla (1856 1943) …   English terms dictionary

• tesla — [tes′lə] n. [after TESLA Nikola] the basic unit of magnetic flux density in the SI and MKS systems, equal to one weber per square meter (10,000 gauss): abbrev. T …   English World dictionary

• tesla — unit of magnetic flux density equal to one weber per square meter Units of Measurement …   Phrontistery dictionary

• tesla — In the SI system, the unit of magnetic flux density expressed as kg s–2 A–1; equal to 1 Wb/m2. [N. T.] * * * tes·la tes lə n a unit of magnetic flux density in the mks system equivalent to one weber per square meter Tesla Nikola (1856 1943)… …   Medical dictionary

• Tesla — Nikola, Serbian American electrical engineer, 1856–1943. See t., T. current. * * * tes·la tes lə n a unit of magnetic flux density in the mks system equivalent to one weber per square meter Tesla Nikola (1856 1943) American electrical engineer… …   Medical dictionary