A DC motor is designed to convert electrical energy into mechanical energy through the interaction between magnetic fields and the current flowing through the armature. This transformation allows the motor to produce motion, which is the primary function of a DC motor.
What type of machine is a synchronous motor?
A Brushless machine
B DC machine
C AC machine
D Induction machine
A synchronous motor is an alternating current (AC) machine that operates at a constant speed, called synchronous speed, which is determined by the supply frequency and the number of poles in the motor. It is commonly used for high‐efficiency applications in AC systems.
In a DC motor, what component reverses the direction of current flow in the armature?
A Commutator
B Field windings
C Stator
D Rotor
The commutator in a DC motor is responsible for reversing the direction of current flow in the armature winding as the motor rotates. This allows for continuous rotation by ensuring that the armature is always subjected to the correct direction of current.
What is the primary cause of efficiency losses in electrical machines?
A Electrical losses
B Magnetic losses
C Mechanical losses
D Core losses
Core losses, also known as iron losses, are caused by hysteresis and eddy currents in the iron core of a machine. These losses are inevitable but minimized through proper design, material selection, and operating conditions.
What does “slip” refer to in an induction motor?
A The torque produced by the motor
B The voltage difference across the motor
C The speed difference between rotor and stator
D The resistance of the motor
Slip in an induction motor is the difference between the synchronous speed (the speed of the magnetic field) and the actual speed of the rotor. Slip is necessary for the generation of torque in an induction motor.
Which of the following motors is typically used in robotics for precise control?
A Synchronous motor
B Stepper motor
C Induction motor
D DC motor
Stepper motors are commonly used in robotics for precise control of position, speed, and rotation. They move in discrete steps, which allows for accurate control, making them ideal for applications requiring high precision.
What is the function of field windings in a DC motor?
A To generate a magnetic field
B To support the rotor
C To reduce losses
D To control the speed of the motor
Field windings in a DC motor generate a magnetic field, which interacts with the current in the armature windings to produce mechanical torque. The strength of this field influences the motor’s speed and performance.
Which of the following is not a method of starting a squirrel-cage induction motor?
A Direct-on-line starting
B Star-delta starting
C Commutator starting
D Autotransformer starting
Commutator starting is not used in induction motors. Induction motors do not require a commutator, as they rely on electromagnetic induction. Star-delta, autotransformer, and direct-on-line are common starting methods for squirrel-cage motors.
In an induction motor, what is the purpose of the rotor?
A To generate a magnetic field
B To control the speed
C To supply power to the stator
D To provide mechanical energy
The rotor in an induction motor receives electrical energy via electromagnetic induction from the stator and converts it into mechanical energy. This energy is used to drive the load connected to the motor.
What type of loss is minimized by using laminated cores in electrical machines?
A Copper losses
B Hysteresis losses
C Eddy current losses
D Mechanical losses
Laminated cores in electrical machines are used to reduce eddy current losses. These losses occur when circulating currents are induced in the core, and laminating the core limits the path for these currents, thus reducing the losses.
In a synchronous motor, what causes the motor to run at synchronous speed?
A The supply frequency
B The load torque
C The rotor’s speed
D The field winding’s strength
In a synchronous motor, the speed of the motor is directly related to the frequency of the alternating current (AC) supply and the number of poles in the motor. The motor runs at this constant speed (synchronous speed), regardless of the load.
Which of the following is a characteristic of a permanent magnet motor?
A Large size
B High torque at low speeds
C High efficiency
D Requires external excitation
Permanent magnet motors are known for their high efficiency because they do not require external excitation for generating the magnetic field. This reduces the need for additional energy, making them more efficient than many other motor types.
What is the main purpose of the commutation in a DC motor?
A To reduce torque ripple
B To increase motor speed
C To prevent overheating
D To reverse current direction
Commutation in a DC motor involves reversing the current direction in the armature windings using the commutator. This ensures continuous rotational motion by maintaining the correct polarity in the armature at all times.
What does “voltage regulation” refer to in electrical machines?
A The ability to maintain constant voltage under varying load conditions
B The rate of change in current
C The ability to reduce heat generation
D The ability to maintain constant speed
Voltage regulation refers to a machine’s ability to maintain a constant output voltage despite fluctuations in load. This is essential in ensuring the stable operation of electrical equipment powered by the machine.
Which loss is mainly due to the resistance of the windings in a motor?
A Mechanical loss
B Copper loss
C Core loss
D Eddy current loss
Copper losses occur due to the resistance in the windings of the motor, causing energy to be dissipated as heat. These losses are a major factor in the overall efficiency of electrical machines.