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Tesla coil
Question: How does a tesla coil work?
Answer:
This device, called a Tesla coil or an Induction coil, which is the basis of many ignition systems for cars, uses the mutual inductance between two coils to produce a high voltage.
A primary coil consisting of a small number of turns of thick copper wire is wound round a
bundle of soft iron rods which are insulated from each other. The secondary coil, which may
consist of many hundreds of metres of fine wire, is wound over the primary.
On closing the switch a current flows in the primary and magnetises the core, which attracts
the armature and breaks the primary circuit. The magnetic field dies away; the armature is
pulled back by the spring and the current flows again. The process then repeats itself.
The rapidly changing magnetic field produces a high voltage in the primary coil; the greater
the rate at which this field changes, the greater is the induced voltage. A capacitor is
connected across the make and break contacts; this reduces sparking and also causes the
field to die away much more rapidly than if the capacitor had not been present. As a result
the induced voltage in the secondary is much greater when the circuit is broken than when it
is made. The secondary current therefore pulsates, but it is always in the same direction.
Sparks of several centimetres in length may be obtained through air at atmospheric pressure
with quite small induction coils, and larger coils were originally used to power X-ray tubes.