Magnetic Lines of Force (MMF)

Lines of magnetic force (MMF) have an effect on adjacent conductors and even itself. This effect is most pronounced if the conductor overlaps itself as in the shape of a coil.

Figure. Magnetic Self-Inductance

Any current-carrying conductor that is coiled in this fashion forms an Inductor, named by the way it induces current flow in itself (selfinductance) or in other conductors.


Inductance (L, Henrys)

Opposition to current flowing through an inductor is inductance. This is a circuit property just as resistance is for a resistor. The inductance is in opposition to any change in the current flow. The unit of inductance is Henry (H) and the symbol is L.


Frequency (f, Hertz)

Any electrical system can be placed in one of two categories direct current (dc) or alternating current (dc). In dc systems the current only flows in one direction. The source of energy maintains a constant electromotive force, as typical with a battery. The majority of electrical systems are ac. Frequency is the rate of alternating the direction of current flow. The short form is f and units are cycles per second or Hertz (short-formed to Hz).


Reactance (X, Ohms)

The opposition to alternating current (ac) flow in capacitors and inductors is known as reactance. The symbol for capacitive reactance is XC and for inductive reactance XL.

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Magnetic Flux (Unit of Measurement is Webers)

When current flows in a conductor, a magnetic field is created around that conductor. This field is commonly presented as lines of magnetic force and magnetic flux refers to the term of measurement of the magnetic flow within the field. This is comparable to the term current and electron flow in an electric field. The following illustration shows the direction of magnetic flux around a conductor and the application of the easily remembered right-hand-rule. Mentally, place your right hand around the conductor with the thumb pointing in the direction of current flow and the fingers will curl in the direction of magnetic flux.

Although we will not go into the derivation of the values, it can be shown that when f is the frequency of the ac current:

XL= 2 (Phi) f L

XC=1/2(Phi)fC

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