When electrons move through a wire, they cause an electromagnetic field to encircle the wire, and when the wire is wrapped around as a coil, an even stronger field is created. By using coils of wire, electromagnets, solenoids and motors are possible.
Properties Of A Coil
When a piece of wire is wrapped into a coil, it resists rapid changes in the current, but will allow steady DC current to pass freely, so high frequency waves and square waves change as a result of the coil’s resistance. Sometimes, the coil will self-oscillate (ringing) to a square wave that passes through. This may happen when there is a high resistance in the external current path in parallel resonant circuits or when there is a low resistance with a series inductance and capacitance.
Some of the energy that is in the field around a coil can be induced into a nearby coil. This is how transformers are made possible.
Types of coils
Tuning coil: Radios used to (and some still do) make use of coils to select a particular signal. The inductance of tuning coils can be varied (hence their resonant frequency) because they have a movable core.
Antenna Coil: Radios use a widely tuned coil to pick up radio signals.
Choke: Chokes are used as a way of suppressing fluctuating signals while a steady current is being passed.
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