Magnetic field lines form in concentric circles around a cylindrical current-carrying conductor, such as a length of wire. The direction of such a magnetic field can be determined by using the "right hand grip rule" (see figure at right). The strength of the magnetic field decreases with distance from the wire. (For an infinite length wire the strength is inversely proportional to the distance.) Bending a current-carrying wire into a loop concentrates the magnetic field inside the loop while weakening it outside. Bending a wire into multiple closely spaced loops to form a coil or "solenoid" enhances this effect. A device so
Inductive discharge ignition in the wire. This voltage jumps across the gap of either the ignitor or a spark plug located in the combustion chamber and ignites the air-fuel mixture to do work. Some magnetos have a second coil of wire located next to the first, called a secondary coil. This coil is usually much longer than the primary loop, accomplished by many more loops around the magnetic core. As the magnetic field is built, it induces a current in the secondary coil as well. When the contact breaker opens the circuit, the magnetic field collapses, causing a high electric voltage in the