What is the primary function of a generator?
A To step down voltage
B To step up voltage
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 machineโs 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.