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Unit 3: Fundamentals of Electrical Machines - Practice Quiz

ECE131 — Basic Electrical And Electronics Engineering 50 Questions
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1 Fleming's Left Hand Rule is primarily used to find the direction of which of the following?

A. Flux density in a solenoid
B. Induced EMF in a generator
C. Magnetic field around a wire
D. Force experienced by a current-carrying conductor in a magnetic field

2 In Fleming's Right Hand Rule, what does the forefinger represent?

A. Direction of Induced EMF
B. Direction of Motion
C. Direction of Current
D. Direction of Magnetic Field

3 What is the primary working principle of a transformer?

A. Lorentz force
B. Static electricity
C. Self-induction
D. Mutual induction

4 Which of the following quantities remains constant in an ideal transformer?

A. Frequency
B. Impedance
C. Voltage
D. Current

5 If a DC supply is connected to the primary of a transformer, what is the likely outcome?

A. It works as an ideal transformer
B. The transformer windings may burn out
C. The secondary voltage is double the primary
D. The frequency increases

6 The EMF equation of a single-phase transformer is given by which formula?

A.
B.
C.
D.

7 What defines the turns ratio () of a transformer?

A.
B.
C.
D.

8 In a Step-Up transformer, which of the following conditions is true?

A. and
B. and
C. and
D. and

9 What is the main advantage of an auto-transformer over a two-winding transformer?

A. Higher frequency operation
B. Ability to handle DC
C. Saving in copper material
D. Isolation between input and output

10 Current Transformers (CT) and Potential Transformers (PT) are collectively known as:

A. Auto-transformers
B. Instrument Transformers
C. Distribution Transformers
D. Power Transformers

11 Why must the secondary of a Current Transformer (CT) never be left open while the primary is energized?

A. It will develop dangerously high voltage across the secondary
B. It will draw zero current
C. The frequency will drop to zero
D. The measurement accuracy increases

12 The core of a transformer is laminated to reduce:

A. Copper loss
B. Hysteresis loss
C. Friction loss
D. Eddy current loss

13 Which principle governs the working of a DC generator?

A. Self-Induction
B. Dynamically induced EMF
C. Mutual Induction
D. Static Induction

14 What is the function of the commutator in a DC generator?

A. To convert induced AC to DC output
B. To convert DC to AC
C. To reduce friction
D. To cool the armature

15 The back EMF () in a DC motor is proportional to:

A.
B.
C.
D.

16 Which DC motor has the highest starting torque?

A. DC Shunt Motor
B. Cumulative Compound Motor
C. DC Series Motor
D. Differential Compound Motor

17 Why should a DC Series motor never be started without a load?

A. It will stall
B. The torque will be zero
C. It will draw zero current
D. It will run at dangerously high speed

18 A DC Shunt motor is also known as a:

A. Variable speed motor
B. Constant current motor
C. High torque motor
D. Constant flux motor

19 The purpose of a starter in a DC motor is to:

A. Reverse the direction
B. Control the speed
C. Limit the high starting current
D. Increase the starting torque

20 To control the speed of a DC motor above its rated (base) speed, which method is used?

A. Armature resistance control
B. Voltage control
C. Ward-Leonard method
D. Field flux control

21 To reverse the direction of rotation of a DC motor, one must:

A. Reverse both the field and armature terminals
B. Reduce the supply voltage
C. Reverse the supply terminals
D. Reverse either the field or the armature terminals

22 Which motor is best suited for electric traction (trains)?

A. DC Series Motor
B. Induction Motor
C. DC Shunt Motor
D. Synchronous Motor

23 The synchronous speed () of an AC machine is given by:

A.
B.
C.
D.

24 What is the working principle of a 3-phase Induction Motor?

A. Production of back EMF
B. Commutation
C. DC excitation
D. Production of Rotating Magnetic Field (RMF)

25 In an induction motor, 'Slip' () is defined as:

A.
B.
C.
D.

26 If the slip of an induction motor is zero, the rotor speed is:

A. Infinite
B. Zero
C. Equal to synchronous speed
D. Half of synchronous speed

27 Why can an induction motor never run at synchronous speed?

A. The relative speed would be zero, inducing no rotor current
B. Stator impedance
C. Air gap reluctance
D. Friction losses

28 The frequency of rotor current () in an induction motor running at slip is:

A.
B.
C.
D.

29 Which part of a DC machine acts as the mechanical support for the poles?

A. Brush
B. Commutator
C. Armature
D. Yoke

30 A Single Phase Induction Motor is:

A. DC operated
B. Not self-starting
C. A synchronous motor
D. Self-starting

31 How is a single-phase induction motor made self-starting?

A. By using a heavy rotor
B. By using DC supply
C. By increasing supply voltage
D. By adding an auxiliary winding to create a phase difference

32 Which motor is commonly used in ceiling fans?

A. Single phase permanent capacitor induction motor
B. Permanent Magnet Synchronous Motor
C. DC Series Motor
D. Universal Motor

33 In a transformer, electrical energy is transferred from primary to secondary via:

A. Air
B. Magnetic Flux
C. Copper wires directly
D. Electrostatic field

34 A transformer has 200 turns in primary and 400 turns in secondary. If input is 100V, output voltage is:

A. 200V
B. 50V
C. 100V
D. 400V

35 Which loss in a transformer is variable and depends on load current?

A. Copper loss
B. Eddy current loss
C. Hysteresis loss
D. Iron loss

36 Fleming's Right Hand Rule is applicable for:

A. Transformer
B. Battery
C. DC Generator
D. DC Motor

37 In a DC machine, the armature winding is placed on the:

A. Rotor
B. Stator
C. Poles
D. Yoke

38 The condition for maximum efficiency in a transformer is:

A. Copper Loss = 0
B. Copper Loss = 2 Iron Loss
C. Copper Loss = Iron Loss
D. Iron Loss = 0

39 Which instrument transformer is connected in series with the line?

A. Current Transformer (CT)
B. Distribution Transformer
C. Auto-transformer
D. Potential Transformer (PT)

40 What is the unit of Mutual Inductance?

A. Henry
B. Farad
C. Ohm
D. Tesla

41 Applications of a DC Shunt Motor include:

A. Heavy construction trucks
B. Electric Locomotives
C. Lathe Machines and Centrifugal Pumps
D. Cranes and Hoists

42 Squirrel cage induction motors are preferred over wound rotor types because:

A. They allow external resistance insertion
B. They are rugged, cheaper, and require less maintenance
C. They run at synchronous speed
D. They have higher starting torque

43 The speed of a 4-pole induction motor connected to a 50Hz supply will be slightly less than:

A. 3000 RPM
B. 1000 RPM
C. 1500 RPM
D. 1200 RPM

44 Which method is used for speed control of a DC motor below its base speed?

A. Frequency Control
B. Pole changing
C. Armature Resistance Control
D. Flux Control

45 In a transformer, the primary and secondary voltages are related by:

A.
B.
C.
D.

46 A Universal Motor can operate on:

A. DC only
B. AC only
C. Three-phase supply only
D. Both AC and DC

47 The rotating magnetic field in a 3-phase induction motor rotates at:

A. Synchronous speed
B. Rotor speed
C. Variable speed
D. Slip speed

48 What is the function of the brushes in a DC machine?

A. To collect or supply current to the rotating armature
B. To reduce eddy currents
C. To generate magnetic field
D. To support the shaft

49 Which type of transformer is used for welding purposes?

A. Step-up transformer
B. Instrument transformer
C. Step-down transformer
D. Current transformer

50 Ideally, the resistance of the primary and secondary windings of a transformer should be:

A. Infinite
B. Zero
C. Very high
D. Equal to load resistance
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