Magnetic field density

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. It is a response of a medium to the presence of a magnetic field. The SI unit of magnetic flux density is the tesla. 1 tesla = 1 weber per square metre.

Related Topics:
Magnetic field - Gravitational - Electric field - SI - Tesla - Weber - Square metre

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It can be more easily explained if one works backwards from the equation: B=rac {F} {I L} ,

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where

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:B is the magnitude of flux density in teslas

Related Topics:
Flux - Teslas

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:F is the force in newtons experienced by a wire carrying

Related Topics:
Force - Newton

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:I amperes of current

Related Topics:
Ampere - Current

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:L metres in length

Related Topics:
Metre - Length

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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.

Related Topics:
Newton - Metre - Ampere

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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' 20 T.

Related Topics:
Superconducting - Electromagnet

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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.

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Indeed, the equation can be adjusted to incorporate moving single charges, ie protons, electrons, and so on via

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F = BQv ,

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where

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:Q is 1 coulomb of charge

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:v is the velocity of that charge in metre per second

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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.

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Other units of magnetic flux density are

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• 1 gauss = 10^-4 teslas = 100 microteslas (µT)
• 1 gamma = 10^-9 teslas = 1 nanotesla (nT)
 
Magnetic field density: See also ►