Final answer:
The breaker points in a magneto are closed by a spring. The spring ensures mechanical, timely operation of the magneto to generate the spark necessary for ignition in an engine. The pinch effect, while related to magnetic forces, does not provide the closing force for breaker points.
Step-by-step explanation:
The closing force for the breaker points in a magneto is provided by a spring. A magneto generates a high voltage by rapidly spinning a magnet in front of a wire coil, inducing a current which can jump across the gap in the breaker points to provide a spark. This spark is necessary to ignite the fuel-air mixture in an internal combustion engine. The process of generating this spark involves converting electrical energy into mechanical work and exploiting the magnetic fields produced by currents, as described by Ampère's Law. The pinch effect mentioned can be observed in various scenarios, including electric arcs, where currents squeeze into a smaller tube due to magnetic forces, and in solar plasmas where magnetic forces shape solar flares. However, this is not the force that closes the breaker points in a magneto. Instead, the breaker points are closed mechanically by a spring return mechanism, which ensures that the points open and close at the correct times for proper engine function.