Transformers MCQs

1. What is the primary function of a transformer?
A) Voltage regulation
B) Current regulation
C) Power conversion
D) Signal amplification
Answer: A

2. Which material is commonly used for the core of a transformer?
A) Copper
B) Aluminum
C) Steel
D) Brass
Answer: C

3. Transformers operate on the principle of:
A) Electromagnetic induction
B) Electric conduction
C) Nuclear fusion
D) Chemical reaction
Answer: A

4. The ratio of the number of turns in the primary winding to the number of turns in the secondary winding of a transformer determines its:
A) Impedance
B) Frequency
C) Voltage ratio
D) Power factor
Answer: C

5. Which type of transformer core offers low hysteresis loss and eddy current loss?
A) Air-core
B) Iron-core
C) Ferrite-core
D) Laminated-core
Answer: D

6. A step-up transformer:
A) Increases voltage and decreases current
B) Decreases voltage and increases current
C) Increases both voltage and current
D) Decreases both voltage and current
Answer: A

7. In a transformer, the primary and secondary windings are magnetically coupled through the:
A) Insulating material
B) Core material
C) Cooling fins
D) Tap changer
Answer: B

8. Which of the following is not a type of transformer based on construction?
A) Shell-type
B) Core-type
C) Step-down type
D) Toroidal
Answer: C

9. The efficiency of a transformer is typically highest when:
A) Loaded close to full capacity
B) Loaded at half of its capacity
C) Loaded below 10% of its capacity
D) Unloaded
Answer: A

10. The frequency of the output voltage of a transformer is:
A) Always equal to the frequency of the input voltage
B) Directly proportional to the number of turns in the windings
C) Inversely proportional to the number of turns in the windings
D) Equal to zero
Answer: A

11. Transformers are rated in terms of:
A) Voltage and current
B) Voltage and power
C) Power and efficiency
D) Frequency and impedance
Answer: B

12. The cooling of large transformers is generally achieved by:
A) Immersion in cooling oil
B) Air circulation around the windings
C) Forced air cooling using fans
D) All of the above
Answer: D

13. Which of the following is an advantage of a three-phase transformer over three single-phase transformers?
A) Lower cost
B) Higher efficiency
C) Better voltage regulation
D) Greater reliability
Answer: A

14. A transformer works based on the principle of:
A) Faraday’s Law of Electromagnetic Induction
B) Ohm’s Law
C) Newton’s Law of Motion
D) Boyle’s Law
Answer: A

15. The insulation resistance of a transformer winding is tested using:
A) Megger
B) Multimeter
C) Oscilloscope
D) Voltmeter
Answer: A

16. Transformers used in electrical power distribution typically operate at:
A) Low voltage and high current
B) High voltage and low current
C) High voltage and high current
D) Low voltage and low current
Answer: B

17. The leakage flux in a transformer is minimized by:
A) Using high permeability core material
B) Increasing the number of turns in the windings
C) Properly insulating the windings
D) Using a closed magnetic circuit
Answer: D

18. Which of the following is true for an autotransformer?
A) It has separate primary and secondary windings
B) It can only step up voltage
C) It is less efficient than a conventional transformer
D) It has a single winding tapped at different points
Answer: D

19. The term “kVA” in transformer ratings stands for:
A) Kilo-Volt Amperes
B) Kilo-Volt Alternating
C) Kilogram-Volt Amperes
D) None of the above
Answer: A

20. Transformers are used extensively in:
A) Audio amplifiers
B) Microwave ovens
C) Electric vehicles
D) Power transmission and distribution
Answer: D

21. The purpose of the oil in an oil-immersed transformer is to:
A) Cool the windings
B) Increase the electrical resistance
C) Decrease the efficiency
D) Reduce the voltage
Answer: A

22. In a delta-star transformer connection, the primary winding is connected in:
A) Delta and secondary in star
B) Star and secondary in delta
C) Both in delta
D) Both in star
Answer: A

23. A current transformer is used to:
A) Step up or step down voltage
B) Measure high currents accurately
C) Isolate two circuits electrically
D) Control the speed of a motor
Answer: B

24. A transformer with a turns ratio of 1:4 will:
A) Step up the voltage by a factor of 4
B) Step down the voltage by a factor of 4
C) Step up the current by a factor of 4
D) Step down the current by a factor of 4
Answer: A

25. The main cause of transformer losses is:
A) Hysteresis
B) Eddy currents
C) Copper losses
D) Dielectric losses
Answer: C

26. Which parameter does not affect the efficiency of a transformer?
A) Load power factor
B) Operating frequency
C) Ambient temperature
D) Insulation resistance
Answer: D

27. A variable voltage transformer is also known as a:
A) Rectifier
B) Variac
C) Transformer tap changer
D) Flyback converter
Answer: B

28. Which of the following statements about transformers is false?
A) Transformers can only work with alternating current
B) Transformers can step up or step down voltage
C) Transformers change the frequency of the electrical signal
D) Transformers can be used to isolate circuits
Answer: C

29. The cooling fins on a transformer are used to:
A) Increase the efficiency
B) Reduce the noise
C) Increase the surface area for heat dissipation
D) Improve the insulation
Answer: C

30. The efficiency of a transformer is defined as:
A) Output power divided by input power
B) Input power divided by output power
C) Output voltage divided by input voltage
D) Output current divided by input current
Answer: A

31. A transformer with 100 turns in the primary winding and 200 turns in the secondary winding will have a turns ratio of:
A) 0.5
B) 1
C) 2
D) 0.667
Answer: C

32. In a transformer, the losses due to magnetization and demagnetization of the core are known as:
A) Hysteresis losses
B) Eddy current losses
C) Copper losses
D) Dielectric losses
Answer: A

33. The voltage regulation of a transformer refers to its ability to:
A) Maintain a constant voltage under varying loads
B) Change the output voltage with load changes
C) Reduce the voltage ripple
D) Step up or step down voltage
Answer: A

34. A transformer that can increase or decrease the voltage level is called a:
A) Step-up transformer
B) Step-down transformer
C) Variable transformer
D) Autotransformer
Answer: D

35. The efficiency of a transformer tends to decrease with:
A) Higher load power factor
B) Lower load power factor
C) Higher operating frequency
D) Lower ambient temperature
Answer: B

36. The primary and secondary windings of a transformer are:
A) Electrically connected
B) Inductively coupled
C) Thermally insulated
D) Made of different materials
Answer: B

37. A transformer designed to step down 240V AC to 12V AC would have a turns ratio of:
A) 20:1
B) 2:1
C) 1:20
D) 1:2
Answer: C

38. A transformer that transfers electrical energy from one circuit to another without a direct electrical connection is an example of:
A) A generator
B) An isolator
C) A motor
D) A transformer
Answer: D

39. In a transformer, the maximum power transfer occurs when:
A) The primary and secondary windings have the same number of turns
B) The primary voltage is higher than the secondary voltage
C) The load impedance matches the transformer impedance
D) The transformer is operating at no load
Answer: C

40. A transformer rated at 500 kVA with a power factor of 0.8 would have a rated apparent power of:
A) 400 kW
B) 500 kW
C) 625 kW
D) 625 kVA
Answer: D

41. Which of the following is not a type of transformer based on cooling methods?
A) Oil-immersed
B) Air-cooled
C) Water-cooled
D) Air-core
Answer: D

42. A transformer with a high turns ratio will have:
A) High voltage and low current
B) Low voltage and high current
C) High voltage and high current
D) Low voltage and low current
Answer: A

43. The efficiency of a transformer is calculated as:
A) (Output voltage / Input voltage) × 100
B) (Output power / Input power) × 100
C) (Output current / Input current) × 100
D) (Output frequency / Input frequency) × 100
Answer: B

44. Which part of a transformer provides a low reluctance path for the magnetic flux?
A) Winding
B) Core
C) Insulation
D) Enclosure
Answer: B

45. The purpose of laminating the core in a transformer is to:
A) Reduce eddy current losses
B) Increase the weight
C) Improve the insulation
D) Enhance the cooling
Answer: A

46. Transformers used in high-frequency applications often use which type of core material?
A) Copper
B) Iron
C) Ferrite
D) Aluminum
Answer: C

47. Which of the following factors affect the voltage regulation of a transformer?
A) Load power factor
B) Operating temperature
C) Core material
D) All of the above
Answer: D

48. A transformer that has the same number of turns in both the primary and secondary windings is known as a:
A) Step-up transformer
B) Step-down transformer
C) Isolation transformer
D) Autotransformer
Answer: D

49. The voltage across the secondary winding of a transformer is 240V when the primary voltage is 480V. What is the turns ratio?
A) 0.5
B) 1
C) 2
D) 4
Answer: C

50. The losses that occur in a transformer due to the resistance of the windings are called:
A) Hysteresis losses
B) Eddy current losses
C) Copper losses
D) Dielectric losses
Answer: C

Transformers MCQs

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