Final answer:
The voltage in the secondary magneto will be at its highest value when the magnetic flux is at a maximum.
Step-by-step explanation:
In a coil that is rotating in a magnetic field, the emf induced will be at its maximum when the magnetic flux is at a maximum. This means that when the coil is in a position where the magnetic field lines passing through it are at their highest, the voltage in the secondary magneto will be at its highest value. For example, in a rectangular coil that is rotated through one-fourth of a revolution, the magnetic flux changes from its maximum to zero, inducing an emf. This is depicted in Figure 23.20.