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

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

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

3 What is the primary working principle of a transformer?

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

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

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

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

A. The secondary voltage is double the primary
B. It works as an ideal transformer
C. The transformer windings may burn out
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. Isolation between input and output
B. Higher frequency operation
C. Saving in copper material
D. Ability to handle DC

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

A. Auto-transformers
B. Instrument Transformers
C. Power Transformers
D. Distribution 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. The frequency will drop to zero
C. The measurement accuracy increases
D. It will draw zero current

12 The core of a transformer is laminated to reduce:

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

13 Which principle governs the working of a DC generator?

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

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

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

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

18 A DC Shunt motor is also known as a:

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

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

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

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

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

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

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

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

A. Induction Motor
B. Synchronous Motor
C. DC Series Motor
D. DC Shunt 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. Production of Rotating Magnetic Field (RMF)
D. DC excitation

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

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. Friction losses
D. Air gap reluctance

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. Commutator
B. Armature
C. Yoke
D. Brush

30 A Single Phase Induction Motor is:

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

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

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

32 Which motor is commonly used in ceiling fans?

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

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

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

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

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

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

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

36 Fleming's Right Hand Rule is applicable for:

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

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

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

38 The condition for maximum efficiency in a transformer is:

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

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

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

40 What is the unit of Mutual Inductance?

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

41 Applications of a DC Shunt Motor include:

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

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

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

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

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

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

A. Frequency Control
B. Pole changing
C. Flux Control
D. Armature Resistance 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. AC only
B. Both AC and DC
C. Three-phase supply only
D. DC only

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

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

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

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

49 Which type of transformer is used for welding purposes?

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

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

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