Final answer:
Magneto breaker points are optimally timed to open when the change in magnetic flux is at its maximum, in alignment with Faraday's law of electromagnetic induction, ensuring the highest efficiency for engine ignition.
Step-by-step explanation:
Magneto breaker points must be timed to open when the change in magnetic flux is at a maximum. This is because the induced electromagnetic force (emf) in the coil is tied to Faraday's law, indicating that emf is induced by a change in magnetic flux over time. When the rotating magnet in a magneto is positioned so that the flux change is at its peak, the breaker points should open to ensure the maximum electrical output for ignition in engines.
To calculate the magnetic flux through a coil, we use the formula Φ = B * A * cos(θ), where Φ is the magnetic flux, B is the magnetic field strength, A is the area of the coil, and θ is the angle between the field lines and the normal to the area of the coil. The flux will be at its maximum when the angle is zero, as cos(0°) = 1.
The answer to the original question regarding magneto breaker points is c. Greatest magnetic field stress exist in the magnetic circuit, which essentially means when the change in magnetic flux is at its maximum.