Magnetic flux is the amount of magnetic field (or the number of lines of force) produced by a magnetic source. The symbol for magnetic flux is  (Greek letter ‘phi’). The unit of magnetic flux is the weber, Wb Magnetic flux density is the amount of flux passing through a defined area that is perpendicular to the direction of the flux:

Magnetomotive force and magnetic field strength

Magnetomotive force (mmf) is the cause of the existence of a magnetic flux in a magnetic circuit,

where N is the number of conductors (or turns) and I is the current in amperes. The unit of mmf is sometimes expressed as ‘ampere-turns’. However since ‘turns’ have no dimensions, the SI unit of mmf is the