The basic principle of an ignition coil
To produce the required high voltages, ignition coils make use of the relationships that exist between electricity and magnetism.
When an electric current flows through an electrical conductor such as a coil of wire, it creates a magnetic field around the coil.
Simultaneously, the magnetic field or flux will progressively grow to its maximum strength, and will become stable when the electric current is stable.
There are two main factors that affect the strength of the magnetic field:
The higher number of windings in the coil, the stronger the magnetic field.
Using a changing magnetic field to induce an electric current
The movement or change in the magnetic field or magnetic flux induces an electric current into the coil wire.
There are two main factors that affect how much voltage is induced into the coil:
The faster the change (or speed of movement) of the magnetic field and the greater the change in the strength of the magnetic field, the greater the induced voltage.
The greater the number of windings in the coil, the greater the induced voltage.