The foundation of modern electrical engineering was the discovery by Faraday that when the magnetic flux through a loop of wire was varied, a voltage was set up in the wire. This process is called electromagnetic induction.

  • A conductor wound in the form of a coil is called an inductor (or solenoid)
  • An inductor has a strong magnetic field that has many uses
  • Inductance opposes current change
  • An inductor may have its inductance increased by:-
    • adding more turns
    • introducing an iron core through the centre of the turns

Inductance Edit

Inductance is the property by which it opposes the change in current through a circuit.


L = Inductance in Henry N = Number of turns in wire coil A = Area of coil in square ² meter l = Average length of coil in meters

Magnetic of Inductance Edit


L = Inductor in Henrys

Magnetic of Turns Edit

Φ = N B A

A-area of cross section of the coil

Voltage of Coil's Inductance Edit

  = -ξ

Voltage of Coil's Turns Edit


Reactance Edit


Impedance Edit


Phase Angle Edit

For an inductor without resistance, the voltage and current is out of phase by 90o (π/2 radians).

For an inductor with resistance, the voltage and current is out of phase by θ:

Tan θ =   = 2πf L/RL

When there is a change of angle, the frequency also changes. This can be used to shift the frequency:

f = ( 2π / Tanθ ) ( RL / L )

As frequency is one over time:

t = ( Tanθ / 2π ) (L / RL )

Frequency Response Edit

 , Shorted Circuit. I = 0
 , Opened Circuit. I ‡ 0
 , Shorted Circuit. I = V / 2 RL

I - can be drawn, at certain frequency the value of current does not change with. So this circuit can be used as a high pass filter.