C To convert mechanical energy into electrical energy
D To convert electrical energy into mechanical energy
A generator operates on the principle of electromagnetic induction to convert mechanical energy into electrical energy.
Which type of current is supplied to an induction motor?
A Alternating current (AC)
B Direct current (DC)
C Pulsating current
D Constant current
Induction motors are designed to operate on AC supply, which creates a rotating magnetic field in the stator.
What happens to the efficiency of a motor at light load?
A It decreases
B It increases
C It remains constant
D It becomes zero
At light load, a significant portion of the power is consumed in overcoming constant losses, leading to lower efficiency.
What is the primary cause of humming noise in a transformer?
A Copper losses
B Magnetostriction in the core
C Mechanical vibrations in windings
D Eddy current losses
Magnetostriction, a phenomenon where the core expands and contracts due to magnetic field changes, causes the humming noise in transformers.
What is the primary function of a cooling fan in large electrical machines?
A To step up the voltage
B To dissipate heat generated by losses
C To reduce the magnetic field strength
D To increase current
Cooling fans are used in large electrical machines to dissipate heat generated by core, copper, and other losses, preventing overheating.
Which component in a DC motor is responsible for reversing current direction?
A Brushes
B Commutator
C Field winding
D Stator
The commutator in a DC motor reverses the current in the armature winding to ensure unidirectional torque.
What is the primary cause of eddy current losses in electrical machines?
A Friction in moving parts
B Circulating currents in the core
C Resistance in the windings
D Overloading
Eddy current losses are caused by circulating currents induced in the core due to changing magnetic fields.
What is the purpose of a step-down transformer?
A To reduce voltage levels
B To step up current
C To step up voltage
D To increase frequency
A step-down transformer reduces the voltage from a higher level to a lower one for safe distribution of electrical power.
What type of motor is most commonly used in electric traction systems?
A DC series motor
B Induction motor
C Stepper motor
D Synchronous motor
DC series motors are commonly used in electric traction systems due to their high starting torque and ability to handle variable loads.
What is the main loss reduced by laminating the core of electrical machines?
A Hysteresis loss
B Eddy current loss
C Copper loss
D Mechanical loss
Laminating the core reduces eddy current losses by restricting the path for circulating currents in the core material.
What happens to the efficiency of a motor at light load?
A It increases
B It decreases
C It remains constant
D It becomes zero
At light load, a significant portion of the power is consumed in overcoming constant losses, leading to lower efficiency.
What is the primary cause of eddy current losses in electrical machines?
A Friction in moving parts
B Circulating currents in the core
C Resistance in the windings
D Overloading
Eddy current losses are caused by circulating currents induced in the core due to changing magnetic fields.
What is the purpose of a step-down transformer?
A To reduce voltage levels
B To step up current
C To step up voltage
D To increase frequency
A step-down transformer reduces the voltage from a higher level to a lower one for safe distribution of electrical power.
What type of motor is most commonly used in electric traction systems?
A DC series motor
B Induction motor
C Stepper motor
D Synchronous motor
DC series motors are commonly used in electric traction systems due to their high starting torque and ability to handle variable loads.
What is the main loss reduced by laminating the core of electrical machines?
A Hysteresis loss
B Eddy current loss
C Copper loss
D Mechanical loss
Laminating the core reduces eddy current losses by restricting the path for circulating currents in the core material.
What is the main advantage of using a squirrel cage rotor in an induction motor?
A Simple construction and robustness
B High starting torque
C High efficiency at no-load
D Better power factor
The squirrel cage rotor is simple, robust, and cost-effective, making it ideal for most industrial applications.
Which motor is most suitable for precision control in robotics?
A Induction motor
B Stepper motor
C Universal motor
D DC motor
Stepper motors are ideal for precision control as they move in discrete steps, providing accurate position control in robotics and other applications.
What is the function of a damping winding in synchronous machines?
A To suppress oscillations and stabilize the rotor
B To increase rotor resistance
C To increase torque
D To reduce slip
Damping windings reduce rotor oscillations during transient conditions and stabilize the synchronous machine’s operation.
What is the role of insulation in electrical machines?
A To prevent electrical leakage and short circuits
B To reduce friction
C To generate power
D To enhance magnetic flux
Insulation in electrical machines prevents electrical leakage and short circuits, ensuring safe operation and protecting the components.
What happens to the slip in an induction motor when the load increases?
A Slip increases
B Slip decreases
C Slip remains constant
D Slip becomes zero
When the load increases, the rotor speed decreases, and the slip increases to induce more current for generating additional torque.
What is the primary function of a motor starter?
A To increase efficiency
B To reduce noise
C To limit the starting current
D To improve insulation
A motor starter is used to limit the high inrush current during the starting of a motor, protecting both the motor and the power supply system.
Which type of machine is used in hand drills?
A Induction motor
B Stepper motor
C Universal motor
D Brushless DC motor
Universal motors are commonly used in hand drills because they are compact, lightweight, and can operate on both AC and DC supplies.
What does “no-load speed” mean in a DC motor?
A The speed when the current is maximum
B The speed when no external load is applied
C The speed at rated torque
D The speed at maximum efficiency
No-load speed is the speed at which a DC motor runs when there is no mechanical load on its shaft, and only friction and windage losses are present.
What is the primary cause of hysteresis loss in electrical machines?
A Resistance in the windings
B Repeated magnetization and demagnetization of the core
C Heat generated by the rotor
D Air gap in the machine
Hysteresis loss occurs due to repeated magnetization and demagnetization of the core material, which causes energy dissipation as heat.
What is the purpose of a cooling fan in large electrical machines?
A To step up the voltage
B To dissipate heat generated by losses
C To reduce the magnetic field strength
D To increase current
Cooling fans are used in large electrical machines to dissipate heat generated by core, copper, and other losses, preventing overheating.
Which component in a DC motor is responsible for reversing current direction?
A Brushes
B Field winding
C Commutator
D Stator
The commutator in a DC motor reverses the direction of current in the armature winding, ensuring unidirectional torque.
What is the primary cause of copper losses in electrical machines?
A Resistance of the windings
B Hysteresis in the core
C Magnetic flux leakage
D Mechanical vibrations
Copper losses occur due to the resistance in the windings, which causes energy dissipation in the form of heat when current flows through them.
Which type of transformer is used for electrical power distribution?
A Step-up transformer
B Step-down transformer
C Isolation transformer
D Auto transformer
Step-down transformers are used in electrical power distribution to reduce the high transmission voltage to a usable level.
What is the primary cause of hysteresis loss in electrical machines?
A Resistance in the windings
B Repeated magnetization and demagnetization of the core
C Heat generated by the rotor
D Air gap in the machine
Hysteresis loss occurs due to repeated magnetization and demagnetization of the core material, which causes energy dissipation as heat.
What is the purpose of a cooling fan in large electrical machines?
A To step up the voltage
B To dissipate heat generated by losses
C To reduce the magnetic field strength
D To increase current
Cooling fans are used in large electrical machines to dissipate heat generated by core, copper, and other losses, preventing overheating.
Which component in a DC motor is responsible for reversing current direction?
A Brushes
B Field winding
C Commutator
D Stator
The commutator in a DC motor reverses the direction of current in the armature winding, ensuring unidirectional torque.
What is the primary cause of copper losses in electrical machines?
A Resistance of the windings
B Hysteresis in the core
C Magnetic flux leakage
D Mechanical vibrations
Copper losses occur due to the resistance in the windings, which causes energy dissipation in the form of heat when current flows through them.
Which type of transformer is used for electrical power distribution?
A Step-up transformer
B Step-down transformer
C Isolation transformer
D Auto transformer
Step-down transformers are used in electrical power distribution to reduce the high transmission voltage to a usable level.
What is the primary cause of hysteresis loss in electrical machines?
A Resistance in the windings
B Repeated magnetization and demagnetization of the core
C Heat generated by the rotor
D Air gap in the machine
Hysteresis loss occurs due to repeated magnetization and demagnetization of the core material, which causes energy dissipation as heat.
What is the purpose of a cooling fan in large electrical machines?
A To step up the voltage
B To dissipate heat generated by losses
C To reduce the magnetic field strength
D To increase current
Cooling fans are used in large electrical machines to dissipate heat generated by core, copper, and other losses, preventing overheating.
Which component in a DC motor is responsible for reversing current direction?
A Brushes
B Field winding
C Commutator
D Stator
The commutator in a DC motor reverses the direction of current in the armature winding, ensuring unidirectional torque.
What is the primary cause of copper losses in electrical machines?
A Resistance of the windings
B Hysteresis in the core
C Magnetic flux leakage
D Mechanical vibrations
Copper losses occur due to the resistance in the windings, which causes energy dissipation in the form of heat when current flows through them.
Which type of transformer is used for electrical power distribution?
A Step-up transformer
B Step-down transformer
C Isolation transformer
D Auto transformer
Step-down transformers are used in electrical power distribution to reduce the high transmission voltage to a usable level.
What is the primary cause of hysteresis loss in electrical machines?
A Resistance in the windings
B Repeated magnetization and demagnetization of the core
C Heat generated by the rotor
D Air gap in the machine
Hysteresis loss occurs due to repeated magnetization and demagnetization of the core material, which causes energy dissipation as heat.
What is the purpose of a cooling fan in large electrical machines?
A To step up the voltage
B To dissipate heat generated by losses
C To reduce the magnetic field strength
D To increase current
Cooling fans are used in large electrical machines to dissipate heat generated by core, copper, and other losses, preventing overheating.
What is the primary function of an alternator?
A To convert DC to AC
B To generate AC power
C To step up voltage
D To convert mechanical energy into heat
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.