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 Magnetic field density - Definition 

Magnetic field density, otherwise known as magnetic flux density, is essentially what the layman knows as a magnetic field - akin to a gravitational or electric field. The SI unit of magnetic flux density is the tesla. 1 tesla = 1 weber (unit) / square metre.

It can be more easily explained if one work backwards from the equation: <math>B=\frac {F} {I L} \,<math>

where

B is the magnitude of flux density in teslas

F is the force in newtons experienced by a wire carrying

I amperes of current

L metres in length

Demonstration of the left hand rule
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Demonstration of the left hand rule

So, one can see for a magnetic flux density to equal 1 tesla, a force of 1 newton must act on a wire of length 1 metre carrying 1 ampere of current.

1 Newton is a lot of force, and is not easily accomplished. To put it in perspective: the most powerful superconducting electromagnets in the world have flux densities of 'only' 20T.

This is true obviously for both electromagnets and natural magnets, but a magnetic field can only act on moving charge - hence the current, I, in the equation.

Indeed, the equation can be played around with to incorporate moving single charges, ie protons, electrons, and so on via <math>F=BQv<math>

where

Q is 1 coulomb of charge

v is the velocity of that charge in metre per second

Fleming's left hand rule can be used to determine the direction of motion/current/polarity from any two of those, as seen in the example.

Other units of magnetic flux density are

SI units

SI electromagnetism units

edit  (http://www.wordiq.com/definition/Template:SI_electromagnetism_units)

Name Symbol Dimensions Quantity
ampere (SI base unit) A A Current
coulomb C A新 Electric charge, Quantity of electricity
volt V J/C = kg搶2−3−1 Potential difference
ohm Ω V/A = kg搶2−3−2 Resistance, Impedance, Reactance
ohm metre Ω搶 kg搶3−3−2 Resistivity
farad F C/V = kg−1−224 Capacitance
farad per metre F/m kg−1−324 Permittivity
reciprocal farad F−1 kg12−2−4 Elastance
siemens S Ω−1 = kg−1−232 Conductance, Admittance, Susceptance
siemens per metre S/m kg−1−332 Conductivity
weber Wb V新 = kg搶2−2−1 Magnetic flux
tesla T Wb/m2 = kg新−2−1 Magnetic flux density
ampere per metre A/m m−1 magnetic induction
ampere-turns per weber A/Wb kg−1−222 Reluctance
henry H V新/A = kg搶2−2−2 Inductance
henry per metre H/m kg搶−2−2 Permeability
(dimensionless) - - Magnetic susceptibility



de:Magnetische Flussdichte ja:蝤撖摨 nl:Magnetische fluxdichtheid sl:gostota magnetnega polja pt:Densidade do fluxo magn彋ico

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This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Magnetic field density".