In the classic iron filings experiment, it is demonstrated that a magnetic field or flux exists in the space around a conductor carrying current. In this experiment the field has the appearance of spaced circular lines. This is simply the effect on the iron filings sprinkled on the paper. There is no sharply defined limit to this field nor does it exist in lines. The field around a coil can be thought of as low" of flux in the area surrounding a coil. The magnitude of this flux flow is determined by the product of current (I) and the number of turns (N) in the coil, plus the magnetic conductivity of the area surrounding the coil. The property of flux conduction is called permeability (u) the force N • I required to create
the flow is called magnetomotive force (mmf).

(de/dt) : The rate of flux change in maxwells per sec.
B: Core flux density (gauss)
E: Voltage applied rms, peak, or dc (volts)
N: Turn count of the winding
F:  Frequency (hz)
t: Time (seconds)
L: Inductance (henries)
I: Current (amps)
Ae: Core cross sectional area (cm2)

The Magnetics Circuit

Flux Density


Magnetomotive Force