The magnetic voltage, also magnetic flux (Grand Theta or Um), is a measure of the strength of the magnetic field of an electric coil with a number of turns "N" through which a current (I) flows. It is the cause of the magnetic flux (Grand-Phi).
If the field lines run in iron, one speaks of an enclosed magnetic circuit, but if there is an air gap in the magnetic circuit, the magnetic resistance of the air must be overcome in addition to the magnetic resistance of the iron. The total flux (magnetic stress) is the sum of the flux in the air gap and in the magnetic material. For this reason, the air gap should be kept as small as possible in electromagnetic devices.