FAA Powerplant Written Practice Test

How is the secondary coil of a magneto grounded?

1. Through the battery

2. Through the primary coil

3. Through the ignition switch

4. Through the spark plugs

The correct answer is: Through the primary coil

The secondary coil of a magneto is grounded through the primary coil, which is essential for the proper operation of the ignition system. In a typical magneto setup, the primary coil generates a magnetic field when current flows through it. As the magneto rotates, it induces a high voltage in the secondary coil that is necessary to create a spark at the spark plugs. The grounding of the secondary coil occurs through the primary coil's connection to the ignition system, helping to complete the circuit for spark generation. This grounding ensures that the high-voltage output from the secondary coil can effectively be delivered to the spark plugs when needed, thus facilitating the ignition of the air-fuel mixture within the engine's cylinders. Other options, such as grounding through the battery, the ignition switch, or directly through the spark plugs, do not accurately describe the magneto’s operation. The battery is typically used in systems with battery-powered ignition rather than magneto ignition. The ignition switch controls the entire ignition circuit but does not serve as the grounding element for the secondary coil, and the spark plugs are the discharge point for the voltage but not involved in the grounding of the secondary coil.