Final answer:
A magneto produces high voltage to fire a spark plug through transformer action. The spinning of the magnet rapidly changes the magnetic flux through a wire coil, which induces high voltage using Faraday's law of electromagnetic induction.
Step-by-step explanation:
A magneto produces the high voltage required to fire a spark plug by utilizing transformer action. Inside a magneto, a magnet is spun rapidly in front of a coil of wire. As a result, a changing magnetic field intersects the coil, which, according to Faraday's law of electromagnetic induction, induces an electromotive force (emf) or voltage in the coil. The rapid rotation of the magnet greatly increases the rate of change in magnetic flux, leading to the generation of a high voltage across the ends of the wire that forms the gap in the spark plug. Upon reaching a threshold, this voltage results in a spark that can ignite the fuel-air mixture in an internal combustion engine.
Faraday's law is key to understanding the function of the magneto. It states that the induced emf in any closed circuit is equal to the negative of the time rate of change of the magnetic flux through the circuit. When the magnet spins, it continuously changes the magnetic flux through the coil, creating a pulsating or alternating current that can be stepped up to the high voltage needed to bridge the air gap of the spark plug.
Overall, the magneto acts much like a generator, converting mechanical energy into electrical energy. However, unlike typical electric generators that generate continuous electricity for powering electrical devices, a magneto is specifically designed to produce a short, high voltage burst to create a controlled spark.