The rotating field of an alternator is produced by applying what type of power to the rotor?

The correct choice is the application of DC power to the rotor of an alternator to produce the rotating magnetic field. In an alternator, a direct current is supplied to the rotor windings, creating a steady magnetic field. This steady magnetic field is crucial because it interacts with the stator windings, where alternating current (AC) is induced due to the relative motion between the magnetic field and the stator windings.

Using DC ensures that the magnetic field remains constant in direction, allowing for the efficient generation of electricity as the rotor spins. Alternators harness this principle by converting mechanical energy into electrical energy through electromagnetic induction. This method contrasts with directly applying AC power, which would result in a fluctuating magnetic field, making it ineffective for inducing a stable alternating current in the stator.

The concept of magnetic flux pertains more to the concept of magnetic field lines and doesn't directly apply to the power type used for creating the field. Apparent power refers to the combination of active and reactive power in an AC circuit but is not a power source in itself. Thus, the choice of DC power is essential for creating the necessary conditions for an alternator to function effectively.