FAA Powerplant Written Practice Test

How is the secondary coil of a magneto grounded?

1. Through the battery

2. Through the primary coil

3. Directly to the engine block

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 because the primary circuit facilitates the operation of the ignition system. In a magneto, the primary coil is connected to the ignition switch, while the secondary coil is designed to generate high voltage. When the magneto operates, the magnetic field changes, inducing current in the primary coil. This current creates a magnetic field that aligns with the flow of current. When the ignition points open, the breakthrough of the magnetic field induces a high voltage in the secondary coil, which then travels to the spark plugs to ignite the fuel-air mixture. Grounding the secondary coil through the primary coil essentially means that it shares a common return path to the magneto's system. This is an essential part of the ignition system's operation, allowing the generated high voltage to do its job effectively. Understanding the importance of this grounding mechanism clarifies how ignition systems are designed to operate efficiently and ensures that the spark plugs receive the necessary voltage to function correctly.