Ignition Coils are used in automobile systems to generate the high voltages required for the spark in the spark plug. The ignition coil consists of two windings. The primary winding which is connected to the battery and the secondary winding which is connected to the spark plug.
The primary winding is made of thick copper wire of small number of turns while the secondary winding has a higher number of turns and is made of thin wires. The core is made of laminated magnetic material.
Power from the battery flows through a switching circuit to the primary winding which has smaller number of turns. When the spark is to be generated a cam operates the switch in the primary circuit. The current to the ignition coil is interrupted. This causes the magnetic field in the coil to collapse and a high voltage is built up in the secondary winding. This winding is connected to the spark plug and causes the spark across the spark gap.
The voltage generated in the secondary winding can be of the order of thousands of volts.