User:Wolfgang1018/English Expressions

Magnetic Field
In physics, a magnetic field is an entity produced by moving electric charges (electric currents) that exerts a force on other moving charges.

Magnetic field is usually denoted by the symbol $$ \mathbf{B} \ $$.

In SI units, $$ \mathbf{B} \ $$ and $$ \mathbf{H} \ $$ are measured in teslas (T) and amperes per meter (A/m), respectively; or, in cgs units, in gauss (G) and oersteds (Oe), respectively.

Two parallel wires carrying an electric current in the same sense will generate a magnetic field which will cause a force of attraction to each other. This fact is used to generate the value of an ampere of electric current.

Note that while like charges repel and unlike ones attract, the opposite holds for currents: if the current in one of the two parallel wires is reversed, the two will repel.

Like the electric field, the magnetic field can be defined by the force it produces.

Magnetic field density
layman Laie

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

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

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' 20 T.