In a DC generator, what is the function of the commutator?
A Generate power
B Prevent losses
C Control speed
D Reverse current direction
In a DC generator, the commutator reverses the current direction in the armature windings as they rotate. This ensures that the current flows in one direction in the external circuit, providing a direct current output.
What type of current is produced by a DC generator?
A Mixed
B Direct
C Alternating
D Pulsating
A DC generator produces direct current (DC) by converting mechanical energy into electrical energy through the rotation of the armature in a magnetic field. The commutator ensures that the output current flows in one direction.
What is the primary advantage of a squirrel-cage induction motor?
A Simple design
B High cost
C High efficiency
D High torque
A squirrel-cage induction motor is favored for its simple design, reliability, and low maintenance. It doesn’t require brushes or a commutator, making it less complex and durable than other motor types like DC motors.
In a synchronous motor, what must the rotor speed be in relation to the stator?
A Variable
B Faster
C Equal
D Slower
In a synchronous motor, the rotor must rotate at synchronous speed, which is the same as the stator’s rotating magnetic field. If the rotor is not synchronized with the stator, the motor will not operate efficiently.
What is the primary use of an induction motor?
A High-torque applications
B Low-speed applications
C High-speed precision tasks
D General-purpose industrial use
Induction motors are widely used in industrial applications due to their reliability, simple construction, and ability to operate in various conditions. They are used in pumps, fans, compressors, and conveyors, among other applications.
Which component is responsible for generating a rotating magnetic field in a three-phase induction motor?
A Commutator
B Stator
C Brushes
D Rotor
In a three-phase induction motor, the stator generates the rotating magnetic field when three-phase current flows through its windings. This rotating magnetic field induces a current in the rotor, causing it to rotate and produce mechanical power.
What is the role of field windings in a synchronous machine?
A Prevent overheating
B Generate torque
C Create a magnetic field
D Control speed
Field windings in synchronous machines are responsible for creating the magnetic field required for operation. These windings are typically located on the rotor and energized with direct current to produce the magnetic field necessary for the motor’s operation.
In an induction motor, what is the function of the rotor?
A Produce torque
B Generate magnetic field
C Generate current
D Reverse current flow
In an induction motor, the rotor produces torque when the rotating magnetic field from the stator induces current in the rotor conductors. This interaction generates mechanical energy, causing the rotor to turn and drive the attached load.
What type of motor is commonly used in fans and blowers?
A Stepper motor
B DC motor
C Induction motor
D Synchronous motor
Induction motors are commonly used in fans and blowers due to their simplicity, low cost, and durability. These motors can run efficiently at constant speeds, which makes them ideal for applications that require continuous operation, like ventilation systems.
What does the term “slip” refer to in an induction motor?
A Frequency of current
B Speed of rotor
C Resistance of rotor windings
D Difference between rotor and stator speed
Slip in an induction motor refers to the difference between the rotor speed and the synchronous speed of the stator’s rotating magnetic field. Slip is necessary for torque production and varies with load; higher slip indicates greater load.
Which of the following is a characteristic of a brushless DC motor?
A Requires external excitation
B High speed
C No commutator
D Low efficiency
A brushless DC motor operates without a commutator, which reduces maintenance and improves efficiency. The absence of brushes minimizes friction, leading to less wear and tear, and it uses an external electronic controller to manage the rotor’s position.
What is the primary function of a stepper motor in robotics?
A Cooling
B High torque
C Precision control
D Speed control
Stepper motors are used in robotics for precise control of position, rotation, and speed. They move in discrete steps, allowing for accurate and repeatable movements, making them ideal for robotic arms and CNC machines.
What is the role of the armature in an induction motor?
A Produce torque
B Control speed
C Generate magnetic field
D Provide mechanical energy
In an induction motor, the armature (or rotor) produces torque by interacting with the rotating magnetic field generated by the stator. This interaction induces a current in the rotor, causing it to rotate and produce mechanical energy.
What does the term “voltage regulation” indicate in an electrical machine?
A Efficiency
B Ability to maintain voltage under load
C Control of current
D Ability to adjust speed
Voltage regulation refers to the ability of an electrical machine, such as a generator or motor, to maintain a stable output voltage despite changes in load. A well-regulated voltage ensures that electrical devices connected to the system operate correctly.
In a DC motor, what determines the direction of rotation?
A Commutator position
B Stator current
C Field winding
D Armature current
In a DC motor, the commutator determines the direction of rotation by reversing the direction of current in the armature windings at regular intervals. This ensures that the motor continues to rotate in the desired direction.