Transformer MCQ

1. A transformer having 1000 primary turns is connected to a 250-V A.C. supply. For a secondary voltage of 400 V, the number of secondary voltage of 400V, the number of secondary turns should be

1. 1600
2. 250
3. 400
4. 1250

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2. A step –up transformer increases

1. Voltage
2. Current
3. Power
4. frequency

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3. The primary and secondary windings of an ordinary2-winding transformer always have

1. Different number of turns
2. Same size of copper wire
3. A common magnetic circuit
4. Separate magnetic circuit

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4. In a transformer, the leakage flux of each winding is proportional to the current in that winding becauseer always have

1. Ohm’s law applies to magnetic circuits
2. Leakage paths do not saturate
3. The two windings are electrically isolated
4. Mutual flux is confined to the core

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5. In a two-winding transformer, e.m.f. per turn secondary winding is always the induced e.m.f. per turn in primary

1. Equal to k times
2. Equal to 1/k times
3. Equal to
4. Greater than

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6. In relation to a transformer, the ratio 20:1 indicates that

1. There are 20 turns on primary one turn on secondary
2. Secondary voltage is 1/20^thof primary voltage
3. Primary current is 20 times greater than the secondary current
4. For every 20 turns on primary, there is one turn on secondary

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7. In performing the short circuit test of a transformer

1. High voltage side is usually short circuited
2. Low voltage side is usually short circuited
3. Any side is short circuited with preference
4. None of the above

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8. The equivalent resistance of the primary of a transformer having k=5 and R₁=0.1 ohm when referred to secondary becomes __ohm.

1. 0.5
2. 0.02
3. 0.004
4. 2.5

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9. A transformer has negative voltage regulation when its load power factor is

1. Zero
2. Unity
3. Leading
4. Lagging

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10. The primary reason why open circuit test is performed on the low-voltage winding of the transformer is that it.

1. Draw sufficiently large no-load current for convenient
2. Requires least voltage to perform the test
3. Needs minimum power input
4. Involves less core less

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