400 Important Transformer MCQ Question and Answer | PDF Free Download
1.The basic function of a transformer is to change
- AThe level of the voltage
- BThe power levels
- CThe power factor
- DThe frequency
2.In an ordinary transformer which of the following does not change
- AVoltage
- BCurrent
- CFrequency
- DAll of the above
3.The efficiency of a power transformer is around
- A50%
- B60%
- C80%
- D95%
4.In a transformer, electrical power is transferred from primary to secondary
- AThrough air
- BBy magnetic flux
- CThrough insulating medium
- DNone of these
5.The two windings of a transformer are
- AConductively linked
- BInductively linked
- CNot linked at all
- DElectrically linked
6.Transformer action requires a
- AConstant magnetic flux
- BIncreasing magnetic flux
- CAlternating magnetic flux
- DAlternating electric flux
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
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
9.The iron core in a transformer provides a _____path to the main flux
- ALow reluctance
- BHigh reluctance
- CLow resistance
- DHigh conductivity
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
11.A transformer transforms
- AVoltage
- BCurrent
- CVoltage and current
- DFrequency
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.
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
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
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
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
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
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 will 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
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
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