A pulse transformer which is a part of the ignition system. It receives a small amount of electrical voltage from the battery and steps up the low "primary" voltage and amplifies it into a big jolt of voltage of about 20,000 volts, and sends it to the spark plugs via the distributor. It is made of two windings and a core of iron. The primary coil has about 200 turns of relatively heavy wire. The secondary windings may have as much as 22,000 windings of fine wire. As electricity travels through the primary winding, it produces a magnetic field in the coil. When the points open, the magnetic field collapses and the movement of the magnetic field induces current in the secondary windings of the coil. The voltage is stepped up in proportion to the ratio of secondary to primary turns and the distributor directs this high voltage to the spark plug.