An alternator is an AC generator that converts mechanical energy into alternating current (AC) electrical energy using electromagnetic induction.
Why is a centrifugal switch used in a single-phase motor?
A To disconnect the starting winding after reaching sufficient speed
B To control the direction of rotation
C To improve power factor
D To regulate voltage
A centrifugal switch is used to disconnect the starting winding when the motor reaches about 70-80% of its rated speed, reducing power consumption and avoiding overheating.
What is the main use of a transformer?
A To step up or step down voltage levels
B To convert AC to DC
C To convert mechanical energy into electrical energy
D To store electrical energy
Transformers are used to either increase (step up) or decrease (step down) voltage levels in AC systems without changing the frequency.
Which type of current is induced in the secondary winding of a transformer?
A Alternating current (AC)
B Direct current (DC)
C Pulsating current
D Constant current
Transformers operate on alternating current (AC), and the same type of current is induced in the secondary winding due to electromagnetic induction.
What does the term “slip” represent in an induction motor?
A Efficiency of the motor
B The difference between synchronous speed and rotor speed
C Voltage regulation
D Rotor resistance
Slip is the percentage difference between the synchronous speed of the stator’s magnetic field and the actual rotor speed, which is essential for torque production in an induction motor.
What is the primary role of field winding in a DC machine?
A To carry load current
B To produce the magnetic field
C To reduce resistance
D To improve efficiency
Field windings are used to generate the magnetic field required for the operation of DC machines, whether in motors or generators.
Which type of motor is used for elevators?
A Induction motor
B Universal motor
C Stepper motor
D Brushless DC motor
Induction motors are commonly used in elevators due to their durability, high starting torque, and ability to handle variable loads effectively.
What type of loss occurs due to repeated magnetization and demagnetization of the core?
A Hysteresis loss
B Eddy current loss
C Copper loss
D Mechanical loss
Hysteresis loss occurs due to the continuous magnetization and demagnetization of the core material in response to the alternating magnetic field.
What is the primary purpose of a step-down transformer?
A To reduce voltage levels
B To step up voltage
C To convert AC to DC
D To store energy
Step-down transformers reduce the voltage from a high level to a lower level for use in homes or industries.
What is the primary function of rotor bars in an induction motor?
A To carry induced current
B To step up voltage
C To reduce slip
D To increase torque
Rotor bars in an induction motor carry the induced current generated by the rotating magnetic field of the stator, creating torque.
What does the term “core loss” refer to in an electrical machine?
A Losses due to hysteresis and eddy currents in the core material
B Losses due to resistance in the windings
C Losses caused by friction in moving parts
D Losses due to heat generated in the motor
Core loss refers to the losses occurring in the magnetic core of electrical machines, caused by hysteresis (magnetic field reversal) and eddy currents (circulating currents in the core).
Which type of motor is commonly used for precision movement in robotics?
A Stepper motor
B Induction motor
C DC motor
D Universal motor
Stepper motors are used in robotics and other precise applications because they allow for very accurate control of position and movement.
What is the primary advantage of a brushless DC motor over a brushed DC motor?
A Longer lifespan due to the absence of brushes
B Higher torque at low speeds
C Lower cost of construction
D Higher power factor
Brushless DC motors last longer than brushed DC motors because they eliminate the need for brushes, which wear out over time. This also reduces maintenance and increases efficiency.
What type of transformer is used for electrical power distribution?
A Isolation transformer
B Step-down transformer
C Step-up transformer
D Autotransformer
Step-down transformers are used in power distribution systems to reduce high transmission voltages to lower, usable levels.
What is the primary function of rotor bars in an induction motor?
A To carry induced current
B To step up voltage
C To reduce slip
D To increase torque
Rotor bars in an induction motor carry the induced current created by the rotating magnetic field of the stator, which produces the motor’s torque.
What is “core loss” in an electrical machine?
A Losses due to hysteresis and eddy currents in the core material
B Losses caused by friction in moving parts
C Losses due to resistance in windings
D Losses due to heat generated in the machine
Core loss in an electrical machine refers to losses in the core material caused by hysteresis (due to magnetization) and eddy currents (induced in the core by the changing magnetic field).
Which type of motor is commonly used for precision movement in robotics?
A Stepper motor
B Induction motor
C DC motor
D Universal motor
Stepper motors are used in robotics because they allow precise control of movement and are ideal for applications requiring accurate positioning.
What is the primary advantage of a brushless DC motor over a brushed DC motor?
A Longer lifespan due to the absence of brushes
B Higher torque at low speeds
C Lower cost of construction
D Higher power factor
Brushless DC motors last longer than brushed DC motors because they eliminate the need for brushes, which wear out over time. This also reduces maintenance and increases efficiency.
What type of transformer is used for electrical power distribution?
A Isolation transformer
B Step-down transformer
C Step-up transformer
D Autotransformer
Step-down transformers are used in power distribution systems to reduce high transmission voltages to lower, usable levels.
What is the primary function of rotor bars in an induction motor?
A To carry induced current
B To step up voltage
C To reduce slip
D To increase torque
Rotor bars in an induction motor carry the induced current created by the rotating magnetic field of the stator, which produces the motor’s torque.