FAA Powerplant Written Practice Test

When does the greatest density of flux lines occur in a rotating magnet-type magneto?

1. When the magnet is in full alignment with the field shoe faces

2. When the magnet is at rest

3. When the magnet is 90 degrees aligned

4. When the magnet is rapidly spinning

The correct answer is: When the magnet is in full alignment with the field shoe faces

The greatest density of flux lines in a rotating magnet-type magneto occurs when the magnet is in full alignment with the field shoe faces. This alignment allows the magnetic field generated by the rotating magnet to effectively link with the core of the magneto, maximizing the interaction between the magnetic field and the windings. When the magnet is fully aligned, the magnetic flux lines are concentrated and pass through the core area efficiently, generating a strong electromotive force (EMF) in the windings. This phenomenon, known as magnetic coupling, is essential for producing the high voltage necessary for ignition systems in aircraft engines. In contrast, if the magnet is at rest, there would be no change in magnetic field over time, resulting in no induced voltage. When the magnet is at a 90-degree alignment, the magnetic flux linkage is minimized, leading to fewer magnetic lines of force interacting with the core. Rapid spinning of the magnet can generate an EMF, but without proper alignment with the field shoe faces, the density of flux lines remains low. Therefore, proper alignment is critical for maximizing the efficiency and effectiveness of the magneto's operation.