Inductors

Inductive loads transduce electrical energy into a magnetic field.
In a DC circuit the inductor only presents the resistance of the wire (very low).

When an inductor in a DC circuit is de-energized the resulting collapse of the magnetic field causes a current to flow in the opposite direction.
This inductive kick-back can be hazardous in DC motor circuits as it can create "blowback" (arcing) across the switch contacts.

Due to the self inductive forces generated in an inductors coil when AC is applied an induced counter voltage is generated in the opposite vector direction as the applied voltage.

This opposition to current flow (resistance) is called inductive reactance or X_L  and is measured in Ohms. (only measured in AC circuits)

Since rapid field change induces higher voltages, increasing frequency causes increasing inductive reactance.
Inductive reaction is therefore frequency dependant.

f increases   X_L    increases    

f decreases  X_L    decreases

X_{L =    where f = frequency}

Resistance = V/I     measured in OHMs

Electric Motor	Transformer	Electromagnet
		Induction furnace link

> the resulting voltage across a resistive load in an RL circuit is the vector addition of the Voltage applied and the Voltage induced in the inductor which are 180* out phase (pointing in opposite directions)

> the symbol for Inductance is L          (after Lenz)
> the unit of inductance is the Henry   (after  Henry)
> the symbol for inductive reactance is  X_L   
> inductive reactance is measured in OHMs 

nice to know for advanced years .......>>

> inductors cause the current in an AC circuit to go out of phase and LAG the applied Voltage

> this can cause power factor problems which can be corrected by the use of capacitors

X_{L =    where f = frequency}

phase shifting of current in an inductive AC circuit

note the current lags applied voltage by 90*

the phase shifting caused by inductors can be corrected by adding capacitors

Power Factor
 

other interesting things happen when capacitors and inductors are combined such as the creation of resonant frequencies

When resistance and reactance (XL and Xc)   are added vectors must be used since they are out of phase by 90*
notice: XL and Xc  are 180* out of phase