Which type of motor is most commonly used with an AC or DC source of supply?

The correct answer identifies the series motor as commonly used with both AC and DC sources. Series motors are designed to operate effectively under variable load conditions, particularly in DC applications where they provide high starting torque, making them suitable for use in applications such as electric vehicles or cranes. Their design allows the field winding to be connected in series with the armature winding, thus spending less energy at low speeds but maximizing output as needed during higher loads.

Induction motors, while prevalent in AC applications, are typically not designed to be used with a DC supply, as they rely on the alternating current to create a rotating magnetic field. Similarly, permanent magnet motors, which are found in both AC and DC configurations, are not specifically used in the same broad range of applications as series motors. Stepper motors are more specialized, mainly utilized in precise positioning applications and controlled via digital signals rather than as general-purpose motors across both AC and DC systems.

Overall, the series motor's design and flexibility in operation makes it a more common choice for various applications compared to the other motor types listed.