# magnetic flux (F)

The total magnetic field of a coil is called the magnetic flux (Phi). In the model of the magnetic field, this is the total number of magnetic field lines of a coil.

The magnetic flux has the unit volt- second (Vs) with the special unit name Weber (Wb) and results from the product of the magnetic flux density B and the area "A" through which it passes perpendicularly, Phi corresponds to B x A. The unit name Weber is named after the German physicist Wilhelm Eduard Weber (1804 - 1891). According to this, one Weber corresponds to the magnetic flux which produces an electromotive force of 1 volt in one turn when it continuously falls to zero in one second (1 Wb = 1 Vs = `10^-8` Maxwell).

The magnetic flux has the direction of the magnetic field. Outside the magnetic field the field lines run from the north to the south pole. If the field cross-section A is crossed at right angles by the flux Phi, the magnetic flux density "B" results from the quotient of Phi/A.

When passing through air gaps, a part of the field lines runs outside the cross section "A". A stray field Phi(S) is generated, which reduces the total flux Phi(G). The difference between the total flux and the stray field applies to the effective flux.