Transformer MCQ

1.The basic function of a transformer is to change

  • AThe level of the voltage
  • BThe power levels
  • CThe power factor
  • DThe frequency
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Answer:

The level of the voltage

Explanation:

2.In an ordinary transformer which of the following does not change

  • AVoltage
  • BCurrent
  • CFrequency
  • DAll of the above
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Answer:

Frequency

Explanation:

3.The efficiency of a power transformer is around

  • A50%
  • B60%
  • C80%
  • D95%
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Answer:

95%

Explanation:

4.In a transformer, electrical power is transferred from primary to secondary

  • AThrough air
  • BBy magnetic flux
  • CThrough insulating medium
  • DNone of these
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Answer:

By magnetic flux

Explanation:

5.The two windings of a transformer are

  • AConductively linked
  • BInductively linked
  • CNot linked at all
  • DElectrically linked
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Answer:

Inductively linked

Explanation:

6.Transformer action requires a

  • AConstant magnetic flux
  • BIncreasing magnetic flux
  • CAlternating magnetic flux
  • DAlternating electric flux
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Answer:

Alternating magnetic flux

Explanation:

7.The flux created by the current flowing through the primary winding induces emf in

  • APrimary winding only
  • BSecondary winding only
  • CTransformer core only
  • DBoth primary and secondary windings
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Answer:

Both primary and secondary windings

Explanation:

8.The primary and secondary windings of a power transformer always have

  • AA common magnetic flux
  • BSeparate magnetic circuits
  • CWire of same size
  • DSame number of turns
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Answer:

A common magnetic flux

Explanation:

9.The iron core in a transformer provides a _____path to the main flux

  • ALow reluctance
  • BHigh reluctance
  • CLow resistance
  • DHigh conductivity
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Answer:

Low reluctance

Explanation:

10.If rated dc voltage is applied instead of ac to the primary of a transformer

  • ASecondary of transformer will burn
  • BPrimary of transformer will burn
  • CSecondary voltage will be excessively high
  • DThere will be no secondary voltage
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Answer:

Primary of transformer will burn

Explanation:

11.A transformer transforms

  • AVoltage
  • BCurrent
  • CVoltage and current
  • DFrequency
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Answer:

Voltage and current

Explanation:

12.For an ideal transformer the windings should have

  • AMaximum resistance on primary side and least resistance on secondary side
  • BLeast resistance on primary side and maximum resistance on secondary side
  • CEqual resistance on primary and secondary sides
  • DNo ohmic resistance on either side.
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Answer:

No ohmic resistance on either side.

Explanation:

13.The core flux in transformer depends mainly on

  • ASupply voltage
  • BSupply voltage and frequency
  • CSupply voltage frequency and load
  • DSupply voltage and load but independent of frequency
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Answer:

Supply voltage and frequency

Explanation:

14.A transformer steps up the voltage by a factor 100. The ratio of current in the primary to that in the secondary is

  • A1
  • B100
  • C0.01
  • D0.1
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Answer:

100

Explanation:

15.If the applied voltage to a transformer primary is increased by keeping the V/f ratio fixed, then the magnetizing current and the core loss will, respectively:

  • ADecrease and remain the same
  • BIncrease and decrease
  • CBoth remain the same
  • DRemain the same and increase
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Answer:

Remain the same and increase

Explanation:

16.If the applied voltage of a certain transformer is increased by 50% and the frequency is reduced to 50% (assuming that the magnetic circuit remain unsaturated), the maximum core flux density will

  • AChange to three times the original value
  • BChange to 1.5 times the original value
  • CChange to 0.5 times the original value
  • DRemain the same as the original value
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Answer:

Change to three times the original value

Explanation:

17.The applied voltage of a certain transformer is increased by 75%; while the frequency of the applied voltage is reduced by 25%. The maximum core flux density will

  • AIncrease by seven times
  • BIncrease by three times
  • CReduce to one quarter
  • DRemain the same
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Answer:

Increase by three times

Explanation:

18.If the supply frequency of a transformer is increased, keeping the supply voltage constant, then

  • ABoth magnetizing component and core loss component of current ill decrease
  • BBoth magnetizing component and core loss component of current will increase
  • CMagnetizing component of current will increase while core loss component of current will decrease
  • DMagnetizing component of current will decrease while core loss component of current will increase
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Answer:

Both magnetizing component and core loss component of current ill decrease

Explanation:

19.The low voltage winding of a 400/230 V single phase 50 Hz transformer is to be connected to a 25 Hz supply. In order to keep the magnetization current at the same level in both the cases the voltage at 25Hz should be

  • A230V
  • B460V
  • C115V
  • D65V
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Answer:

115V

Explanation:

20.A single-phase transformer rated for 220/240V, 50Hz operates at no load at 220 V, 40 Hz. This frequency operation at rated voltage results in which one of the following?

  • AIncrease of both eddy-current and hysteresis losses.
  • BReduction of both eddy-current and hysteresis losses
  • CReduction of hysteresis loss and increase in eddy-current loss.
  • DIncrease of hysteresis loss and no change in the eddy-current loss
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Answer:

Increase of hysteresis loss and no change in the eddy-current loss

Explanation: