FAA Powerplant Written Practice Test

What indicates that the circuit is closed in a magneto system?

1. Magnetic field presence

2. High voltage transfer

3. Contact points touching

4. Rotating magnet alignment

The correct answer is: Contact points touching

In a magneto ignition system, the indication that the circuit is closed is determined by the contact points touching. In such systems, when the engine is cranked, the rotating magnet within the magneto assembly creates a magnetic field. This field interacts with the armature and induces high voltage in the secondary winding of the ignition coil, but this process only occurs after the circuit is complete. The contact points serve as a switch that allows the circuit to close. When the points come into contact, they complete the electrical circuit, enabling current to flow and facilitating the generation of a spark at the spark plugs. This is crucial for ignition to occur. When the points open, the circuit is broken, interrupting the current flow and stopping the ignition process. Therefore, the touching of the contact points is the definitive indicator that the circuit is indeed closed in a magneto system, leading to the high voltage generation necessary for engine operation.