What type of energy conversion occurs in a generator?
A Electrical to mechanical
B Mechanical to electrical
C Electrical to heat
D Mechanical to thermal
A generator converts mechanical energy into electrical energy using the principle of electromagnetic induction.
What is the stationary part of an induction motor called?
A Rotor
B Armature
C Stator
D Commutator
The stator is the stationary part of an induction motor that contains the winding connected to the power supply.
What is the main function of a slip ring in an AC generator?
A To transfer current to or from the rotating coil
B To rectify AC to DC
C To reduce resistance
D To increase torque
Slip rings provide a continuous electrical connection between the stationary circuit and the rotating coil.
What is the frequency of the induced EMF in the rotor of a squirrel cage induction motor at synchronous speed?
A Zero
B Equal to the supply frequency
C Half of the supply frequency
D Twice the supply frequency
At synchronous speed, the relative motion between the rotor and the magnetic field is zero, so no EMF is induced.
Which type of motor is commonly used for conveyor belts?
A Stepper motor
B Induction motor
C DC motor
D Synchronous motor
Induction motors are commonly used for conveyor belts due to their ruggedness, reliability, and ability to handle varying loads.
What is the primary cause of copper losses in electrical machines?
A Resistance in the windings
B Hysteresis in the core
C Eddy currents in the core
D Magnetic flux leakage
Copper losses occur due to the resistance of the windings, leading to heat generation when current flows through them.
What is the primary role of a capacitor in single-phase motors?
A To increase power output
B To create a phase shift for starting torque
C To reduce losses
D To provide insulation
The capacitor in single-phase motors creates a phase shift between the currents in the start and run windings, enabling the motor to develop starting torque.
What does the term “core saturation” refer to in electrical machines?
A Increased slip in the rotor
B Magnetic core operating at maximum flux density
C Loss of rotor alignment
D Overheating of the windings
Core saturation occurs when the magnetic core operates at its maximum flux density and cannot accommodate additional magnetic flux.
What is the main advantage of using a brushless motor?
A Higher starting torque
B Less maintenance and longer lifespan
C Simplified construction
D Reduced manufacturing cost
Brushless motors eliminate the need for brushes and commutators, reducing maintenance and increasing durability.
What determines the torque produced by an induction motor?
A Voltage applied to the stator
B Rotor material
C Interaction between rotor current and stator magnetic field
D Size of the stator core
Torque in an induction motor is produced by the interaction between the rotor current and the rotating magnetic field of the stator.
What happens to the speed of a DC motor when load increases?
A Increases
B Decreases
C Remains constant
D Becomes zero
The speed of a DC motor decreases with an increase in load due to the drop in terminal voltage caused by increased armature current.
What is the primary function of laminating the core of a transformer?
A To reduce eddy current losses
B To improve cooling efficiency
C To reduce core weight
D To improve voltage regulation
Laminating the core reduces eddy current losses by limiting the flow of induced currents in the core material.
What is the main characteristic of a stepper motor?
A Rotates in discrete steps
B Operates at synchronous speed
C Produces high starting torque
D Requires brushes for operation
Stepper motors rotate in discrete steps, allowing precise control over position and speed.
What does a flywheel help maintain in electrical machines?
A Low power consumption
B Smooth rotational motion
C Reduced current losses
D Stable voltage
A flywheel helps smooth out rotational motion by storing rotational energy and reducing speed fluctuations.
Which part of a synchronous motor determines the rotor speed?
A Supply frequency
B Load torque
C Rotor resistance
D Stator winding
The rotor speed of a synchronous motor is directly proportional to the supply frequency and remains constant.
What is the function of commutators in DC machines?
A To ensure unidirectional current flow
B To reduce core losses
C To step up voltage
D To control slip
Commutators in DC machines reverse the direction of current in the armature winding, ensuring unidirectional torque.
Why are ball bearings used in electrical machines?
A To reduce electrical losses
B To minimize mechanical friction
C To increase magnetic flux
D To maintain constant speed
Ball bearings reduce mechanical friction in rotating parts, improving the machine’s efficiency and longevity.
What is the primary purpose of insulation in electrical machines?
A To prevent electrical leakage
B To increase current
C To regulate speed
D To improve magnetic field strength
Insulation prevents electrical leakage, ensuring safety and proper operation of electrical machines.
Which loss is directly proportional to the square of the load current?
A Core loss
B Copper loss
C Friction loss
D Windage loss
Copper losses are proportional to the square of the load current because they depend on the resistance of the windings and the current flowing through them.
What is the typical cooling method for large electrical machines?
A Natural convection
B Forced air or liquid cooling
C Radiation
D Thermoelectric cooling
Large electrical machines often use forced air or liquid cooling systems to dissipate the heat generated by losses efficiently.