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Unit 3 - Practice Quiz

ECE131

1 Fleming's Left Hand Rule is primarily used to find the direction of which of the following?

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

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

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

3 What is the primary working principle of a transformer?

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

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

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

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 secondary voltage is double the primary
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. Saving in copper material
C. Higher frequency operation
D. Ability to handle DC

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

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

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

A. It will draw zero current
B. It will develop dangerously high voltage across the secondary
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. Eddy current loss
D. Friction loss

13 Which principle governs the working of a DC generator?

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

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

A. To convert DC to AC
B. To convert induced AC to DC output
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. DC Series Motor
C. Cumulative Compound Motor
D. Differential Compound Motor

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

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

18 A DC Shunt motor is also known as a:

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

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

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

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

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

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

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

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

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

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

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

A. Friction losses
B. The relative speed would be zero, inducing no rotor current
C. Stator impedance
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. Armature
B. Commutator
C. Yoke
D. Brush

30 A Single Phase Induction Motor is:

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

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

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

32 Which motor is commonly used in ceiling fans?

A. DC Series Motor
B. Permanent Magnet Synchronous Motor
C. Single phase permanent capacitor induction 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. 50V
B. 100V
C. 200V
D. 400V

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

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

36 Fleming's Right Hand Rule is applicable for:

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

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

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

38 The condition for maximum efficiency in a transformer is:

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

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

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

40 What is the unit of Mutual Inductance?

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

41 Applications of a DC Shunt Motor include:

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

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

A. They have higher starting torque
B. They allow external resistance insertion
C. They are rugged, cheaper, and require less maintenance
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. Flux Control
B. Armature Resistance Control
C. Frequency Control
D. Pole changing

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

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

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

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

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

49 Which type of transformer is used for welding purposes?

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