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.
What is the primary function of the rotor in an electric motor?
A To rotate and produce mechanical output
B To generate electrical power
C To create a magnetic field
D To regulate voltage
The rotor is the rotating part of an electric motor that interacts with the stator’s magnetic field to produce mechanical torque, driving loads.
What is the purpose of a magnetic field in a generator?
A To reduce current losses
B To induce voltage in the armature
C To increase mechanical efficiency
D To step up voltage
In a generator, the magnetic field interacts with the motion of the conductor (armature) to induce voltage, following Faraday’s Law of Electromagnetic Induction.
Which electrical machine operates on the principle of mutual induction?
A DC motor
B Transformer
C Universal motor
D Stepper motor
Transformers operate on the principle of mutual induction, where a change in current in the primary winding induces a voltage in the secondary winding.
What type of motor is commonly used in fans?
A Single-phase induction motor
B DC motor
C Universal motor
D Synchronous motor
Single-phase induction motors are simple, reliable, and commonly used in household fans due to their low cost and ability to operate on AC supply.
What is the primary advantage of a squirrel cage rotor?
A Simple and robust construction
B High starting torque
C High efficiency at all loads
D Easy speed control
Squirrel cage rotors are widely used in induction motors due to their simple, rugged design and ability to work under harsh conditions with minimal maintenance.
Which part of a DC generator is responsible for collecting current?
A Armature
B Brushes
C Field winding
D Yoke
Brushes collect the current from the commutator and transfer it to the external circuit in a DC generator.
What type of winding is used in step-up transformers?
A Series winding
B More turns in the secondary winding than the primary winding
C Less turns in the secondary winding than the primary winding
D Equal turns in primary and secondary windings
In a step-up transformer, the secondary winding has more turns than the primary winding, increasing the voltage while decreasing the current.
What is “harmonic distortion” in electrical machines?
A Deviation in voltage levels
B Presence of unwanted frequencies in the waveform
C Reduction in efficiency
D Sudden voltage drop
Harmonic distortion occurs when unwanted higher-order frequencies are introduced in the voltage or current waveforms, affecting machine performance.
Why is insulation used in electrical machines?
A To prevent electrical leakage and short circuits
B To increase magnetic flux
C To reduce copper losses
D To improve power factor
Insulation is used to prevent electrical leakage between components, protect against short circuits, and ensure safe operation of the machine.
What type of loss occurs due to friction between moving parts in electrical machines?
A Eddy current loss
B Mechanical loss
C Copper loss
D Insulation loss
Mechanical losses are caused by friction in bearings and windage, leading to energy dissipation as heat.
What 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 because they provide high starting torque and are able to handle variable loads effectively.
What is the primary advantage of a squirrel cage rotor?
A Simple and robust construction
B High starting torque
C High efficiency at all loads
D Easy speed control
Squirrel cage rotors are widely used in induction motors due to their simple, rugged design and ability to work under harsh conditions with minimal maintenance.
What is the primary cause of hysteresis loss in electrical machines?
A Eddy currents in the core
B Repeated magnetization and demagnetization of the core material
C Friction in bearings
D Copper resistance in windings
Hysteresis loss occurs due to the continuous magnetization and demagnetization of the core material during the operation of the machine, which results in energy dissipation as heat.
What is the main function of an excitation system in a synchronous machine?
A To supply DC to the field winding
B To regulate rotor speed
C To improve efficiency
D To reduce mechanical losses
The excitation system provides the necessary DC current to the field winding of synchronous machines to create the magnetic field required for operation.
Which type of motor is commonly used in battery-powered toys?
A Induction motor
B Permanent magnet DC motor
C Stepper motor
D Brushless DC motor
Permanent magnet DC motors are commonly used in battery-powered toys because they are compact, efficient, and suitable for low-voltage operation.
What happens to the rotor speed of an induction motor if the load increases?
A It decreases
B It increases
C It remains constant
D It becomes equal to synchronous speed
The rotor speed of an induction motor decreases as the load increases, resulting in a higher slip which induces more current in the rotor to produce more torque.
What is the main advantage of a brushless DC motor?
A No brushes, resulting in less maintenance
B High torque at low speeds
C Simpler construction
D Lower efficiency
Brushless DC motors do not have brushes, which reduces maintenance, increases efficiency, and extends the motor’s lifespan by eliminating wear and tear on the commutator.
What is the main cause of mechanical losses in electrical machines?
A Friction in bearings and windage
B Eddy currents in the core
C Copper losses in windings
D Hysteresis loss in the core
Mechanical losses occur due to friction in bearings and windage (air resistance), which dissipate energy as heat, reducing the machine’s efficiency.
Which component in a motor reduces sparking at the brushes?
A Interpoles
B Stator winding
C Bearings
D Shaft
Interpoles are small auxiliary poles placed between the main poles of a DC machine to improve commutation, reducing sparking at the brushes.
What is the function of commutators in DC motors?
A To ensure unidirectional current in the armature winding
B To increase torque
C To reduce resistance
D To step up voltage
The commutator reverses the direction of current in the armature winding of a DC motor, ensuring unidirectional torque and smooth operation.
What is the primary function of the armature winding in a DC motor?
A To carry current that interacts with the magnetic field to produce torque
B To generate the magnetic field
C To insulate the stator
D To step up voltage
The armature winding in a DC motor carries current, and this current interacts with the magnetic field created by the field winding to produce torque and allow the motor to rotate.
Which type of machine is typically used in domestic water pumps?
A Universal motor
B Single-phase induction motor
C DC motor
D Stepper motor
Single-phase induction motors are widely used in domestic water pumps because of their low cost, simplicity, and reliability in handling moderate loads.
What does the term “synchronous speed” mean in an induction motor?
A The speed of the rotor
B The speed of the magnetic field in the stator
C The speed of the current flow
D The speed of torque generation
Synchronous speed refers to the speed at which the stator’s magnetic field rotates in an induction motor. It depends on the supply frequency and the number of poles.
What type of loss is directly proportional to the square of the current?
A Copper loss
B Core loss
C Eddy current loss
D Windage loss
Copper losses are due to the resistance of the windings and are proportional to the square of the current (I²R).
Which component is responsible for regulating voltage in a transformer?
A Stator
B Rotor
C Tap changer
D Commutator
Tap changers are used to adjust the turns ratio in a transformer, which helps regulate the output voltage as the load conditions change.
What happens when the load on a transformer increases?
A Core losses increase
B Copper losses increase
C Voltage increases
D Eddy current losses decrease
Copper losses increase with load because the current increases, and losses are proportional to the square of the current.
What type of motor is commonly used in electric vehicles?
A Stepper motor
B Brushless DC motor
C Synchronous motor
D Universal motor
Brushless DC motors are commonly used in electric vehicles because they are efficient, offer high torque, and require less maintenance due to the absence of brushes.
What is “harmonic distortion” in electrical machines?
A Deviation in voltage levels
B Presence of unwanted frequencies in the waveform
C Reduction in efficiency
D Sudden voltage drop
Harmonic distortion occurs when non-fundamental frequencies appear in the voltage or current waveforms, leading to inefficiency and potential damage to equipment.
Why is insulation used in electrical machines?
A To prevent electrical leakage and short circuits
B To increase magnetic flux
C To reduce copper losses
D To improve speed
Insulation prevents electrical leakage, protects the machine’s components, and ensures safe operation by avoiding short circuits.
What is the role of a bearing in an electrical machine?
A To support and allow smooth rotation of the shaft
B To increase torque
C To reduce voltage losses
D To generate magnetic fields
Bearings reduce friction between the rotating parts and provide mechanical support, ensuring smooth operation of the motor.
What is the main reason for using silicon steel in transformer cores?
A To reduce hysteresis losses
B To reduce weight
C To improve mechanical strength
D To enhance cooling
Silicon steel has high magnetic permeability and low hysteresis loss, which makes it ideal for transformer cores. It minimizes core losses and improves efficiency.
What type of rotor is used in shaded pole motors?
A Salient pole rotor
B Squirrel cage rotor
C Hollow rotor
D Phase-wound rotor
Shaded pole motors use a squirrel cage rotor, which is simple and robust, making it ideal for small motors such as those used in fans and small appliances.
What is the purpose of the yoke in a DC machine?
A To provide mechanical support and act as a protective cover
B To carry current
C To step up voltage
D To increase speed
The yoke is the outer frame of a DC machine that provides mechanical support and protects the internal components of the machine.
What type of machine is commonly used in electric traction systems?
A DC series motor
B Synchronous motor
C Universal motor
D Induction motor
DC series motors are widely used in electric traction systems, such as locomotives, because they provide high starting torque and can handle variable loads effectively.
What happens to the rotor speed of an induction motor if the load increases?
A It decreases
B It increases
C It remains constant
D It becomes equal to synchronous speed
The rotor speed of an induction motor decreases as the load increases, which increases the slip and allows more torque to be generated.
What is the primary function of a transformer?
A To step up or step down voltage
B To generate electricity
C To convert DC to AC
D To regulate frequency
The main function of a transformer is to step up or step down the voltage while maintaining the frequency of the alternating current.
What happens to the power factor of an induction motor at no load?
A It is very low
B It is very high
C It remains constant
D It becomes unity
At no load, the power factor of an induction motor is low because the motor draws a large reactive current compared to the real current.
Why is silicon steel used in the cores of electrical machines?
A To reduce hysteresis losses
B To reduce weight
C To improve mechanical strength
D To enhance cooling
Silicon steel is used in the cores of electrical machines because it has low hysteresis loss and high magnetic permeability, which improves efficiency.
What type of machine is typically used in battery-powered toys?
A Induction motor
B Permanent magnet DC motor
C Synchronous motor
D Stepper motor
Permanent magnet DC motors are widely used in battery-powered toys due to their simplicity, compact size, and low power requirements.
What is the main function of the cooling system in large electrical machines?
A To dissipate heat generated by losses
B To increase power output
C To improve magnetic flux
D To increase torque
Cooling systems in large electrical machines are used to dissipate the heat generated from various losses (copper, core, etc.) during operation, ensuring safe and efficient functioning.