Magnetic_field_density Magnetic_field_density

Magnetic field density - Definition and Overview

Related Words: Attractive, Charismatic, Diamagnetic, Drawing, Electromagnetic, Enchanting

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·s Electric charge, Quantity of electricity
volt V J/C = kg·m2·s−3·A−1 Potential difference
ohm Ω V/A = kg·m2·s−3·A−2 Resistance, Impedance, Reactance
ohm metre Ω·m kg·m3·s−3·A−2 Resistivity
farad F C/V = kg−1·m−2·A2·s4 Capacitance
farad per metre F/m kg−1·m−3·A2·s4 Permittivity
reciprocal farad F−1 kg1·m2·A−2·s−4 Elastance
siemens S Ω−1 = kg−1·m−2·s3·A2 Conductance, Admittance, Susceptance
siemens per metre S/m kg−1·m−3·s3·A2 Conductivity
weber Wb V·s = kg·m2·s−2·A−1 Magnetic flux
tesla T Wb/m2 = kg·s−2·A−1 Magnetic flux density
ampere per metre A/m m−1·A magnetic induction
ampere-turns per weber A/Wb kg−1·m−2·s2·A2 Reluctance
henry H V·s/A = kg·m2·s−2·A−2 Inductance
henry per metre H/m kg·m·s−2·A−2 Permeability
(dimensionless) - - Magnetic susceptibility


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