M3.12 Cat B

What does a commutator do in a dc machine?

• Increases the speed of the armature
• Regulates the voltage in the field windings
• Controls the temperature of the machine
• Reverses the direction of current in the armature windings

What effect would increasing the armature current have on the armature cross field?

• Reverse
• No effect
• Weaken
• Strengthen

Which component in a dc machine machine provides the power supply for the armature?

• Transformer and rotating diode pack

• Commutator and brushes
• Excitation winding

• Field winding

Why are interpoles fitted to main poles of DC machines?

• To increase armature reaction and commutation problems.
• To reduce armature reaction and commutation problems.
• To decrease the efficiency of the machine.
• To make the machine more prone to overheating.

what is the purpose of the excitation winding in a dc machine?

• To increase the machine's weight
• To cool down the machine
• To create the magnetic field necessary for the operation of the machine.
• To reduce the efficiency of the machine

How is the direction of rotation in a dc machine changed?

• By increasing the resistance in the circuit
• By reducing the number of windings in the armature
• By adding more voltage to the circuit
• By reversing the polarity of the applied voltage or by reversing the connections to the field winding or armature.

What type of motor is best suited as a starter motor?

• Shunt field motor

• Series field motor

• Compound motor

• Stepper motor

What is the advantage of a shunt field motor?

• It has a high efficiency at low speeds
• It is not affected by changes in the load
• It requires less maintenance
• It maintains constant speed even when the load changes.

What is the advantage of a series field motor?

• Low starting torque and inability to operate at variable speeds
• High starting torque and inability to operate at variable speeds
• Low starting torque and ability to operate at fixed speed
• High starting torque and ability to operate at variable speeds

What is the purpose of the commutator?

• To reverse the current in the armature

• To reverse the current in the field windings

• To protect the slip ring from damage

• To allow constant motion of the rotor

• To allow the motor to be used as a generator