DC and AC Machine Fundamentals Quiz

What is the primary function of a commutator in a DC machine?

• To increase the efficiency of the machine

• To convert AC voltage into DC voltage

• To ensure unidirectional current flow in the armature

In a separately excited DC motor, how is the field winding powered?

• By a separate DC source independent of the armature supply

• By the same power supply as the armature

• By an external AC source

What happens to the speed of a DC shunt motor if the field resistance is increased?

• The speed increases

• The speed decreases

• The speed remains constant

What determines the synchronous speed of an AC machine?

• The supply frequency and the number of poles

• The armature resistance and supply voltage

• The rotor current and stator inductance

In an induction motor, what is slip?

• The speed difference between the stator field and the rotor

• The difference in voltage between the stator and rotor

• The loss in efficiency due to copper losses

Why is the rotor of a synchronous motor unable to start on its own?

• It requires an external DC supply to excite the rotor field

• It lacks the slip needed for starting torque like an induction motor

• It has a very high starting current requirement