Tesla (unit)

The tesla (symbol T) is the SI derived unit of magnetic flux density B, (which is also known as "magnetic field"). One tesla is equal to one weber per square meter, and it was defined in 1960 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.

Definition

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).

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 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).

In ferromagnets the movement creating the magnetic field is the electron spin (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).

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

Main article: Orders of magnitude (magnetic field)

• 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

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. 31 µT (3.1×10−6 T) - strength of Earth's magnetic field at 0° latitude (on the equator)

External links

The Wiktionary entry for tesla

• Gauss<->Tesla Conversion Tool