1. The basic function of a transformer is to change
(a) the level of the voltage.
(b) the power level.
(c) the power factor.
(d) the frequency.
Ans : (a) the level of the voltage
2. The efficiency of a power transformer is around
(a) 50%. (b) 60%. (c) 80%. (d) 95%.
Ans : (d) 95%
3. In a transformer, electrical power is transferred from primary to secondary
(a) through air.
(c) through insulating medium.
(b) by magnetic flux.
(d) none of these.
Ans : (b) by magnetic flux
4. The two windings of a transformer are
(a) conductively linked.
(b) inductively linked.
(c) not linked at all.
(d) electrically linked.
Ans :(b) inductively linked.
5.Transformer action requires a
(a) constant magnetic flux.
(b) increasing magnetic flux.
(c) alternating magnetic flux.
(d) alternating electric flux.
Ans : (c) alternating magnetic flux.
6. The flux created by the current flowing through the primary winding induces emf in
(a) primary winding only.
(b)secondary winding only.
(c) transformer core only.
(d)both primary and secondary windings.
Ans: (d)both primary and secondary windings.
7. The primary and secondary windings of a power transformer always have
(a) a common magnetic circuit.
(b) separate magnetic circuits.
(c) wire of same size.
(d) same number of turns.
Ans : (a) a commin magnetic circuit
8. The iron core in a transformer provides a path to the main flux.
(a) low reluctance
(b) high reluctance
(c) low resistance
(d) high conductivity
Ans : (a) low reluctance
9. If rated de voltage is applied instead of ac to the primary of a transformer
(a) secondary of transformer will burn.
(b) primary of transformer will burn.
(c) secondary voltage will be excessively high.
(d) there will be no secondary voltage.
Ans : (b) primary of transformer will burn.
10. A transformer transforms
(a) voltage
(b) current.
(c) voltage and current.
(d) frequency
Ans : (c) voltage and current.
11. Which of the following would refer to an ideal transformer?
1. Winding resistances are negligible.
2. Leakage-fluxes are included.
3. Core-losses are negligible.
4. Magnetization characteristic is linear.
(a) 1,2 and 3 only.
(b) 1, 3 and 4 only.
(c) 1, 2 and 4 only.
(d) 2,3, and 4 only.
12. The flux in transformer core.
(a) increases with load.
(b) decreases with load.
(c) remains constant irrespective of load.
(d) none of the above.
Ans : (c) remains constant irrespective of load.
13. The primary ampere-turns are counter balanced by
(a) secondary ampere-turns.
(b) primary flux
(c) increase in mutual flux.
(d) increase in secondary current.
Ans : (a) secondary ampere-turns.
14. The mutual flux in a loaded transformer can be varied by varying
(a) primary current.
(b) load impedance.
(c) secondary current.
(d) reluctance of the magnetic path.
Ans : (d) reluctance of the magnetic path.
15. In a transformer flux____decreases with the increase in leakage flux.
(a) primary induced emf
(b) secondary induced emf
(c) secondary terminal voltage
(d) none of the above.
Ans : (c) secondary terminal voltage
16. Power transformed from primary to secondary depends upon
(a) number of primary turns.
(b) number of secondary turns.
(c) current transformation ratio.
(d) magnetic coupling between primary and secondary windings.
Ans : (d) magnetic coupling between primary and secondary windings.
17.A transformer is supplying pure resistive (unity pf) load. The power factor on primary side will be
(a) about 0.95 (lead).
(b) about 0.95 (lag).
(c) zero.
(d) unity.
Ans : (b) about 0.95(lag).
18. In a transformer supplying inductive load
(a) the secondary current results in equivalent primary current in phase opposition.
(b) the secondary terminal voltage is less than the secondary induced emf.
(c) the power factor on primary side will be lower than that of load.
(d) all of the above.
Ans : (d) all of the above.
19. The phasor diagram of a transformer on load can be drawn only if we know
(a) equivalent circuit parameters of the transformer.
(b) load current
(c) load pf.
(d) all of the above.
Ans : (d) all of the above.
20. When a transformer is operating on no load, the primary applied voltage is approximately balanced by
(a) primary induced emf.
(b) secondary induced emf.
(c) terminal voltage across the secondary (d) voltage drop across the resistance and reactance.
Ans : (a) primary induced emf.
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