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UNIT- 3 Transformers Multiple Choice Questions 1. A transformer will work on ______ a) A.C only c) Both A.C and D.C Ans: a) A.C Only. b) D.C only d) None of the above 2. Transformer cores are laminated in order to a) Decrease iron loss b) Prevent eddy current loss c) Eliminate magnetic hysteresis d) none of the above Ans: b) Prevent eddy current loss. 3. An ideal transformer is one which a) Has no losses and leakage reactance b) Does not work c) Has same number of primary and secondary turns d) none of the above Ans: a) Has no losses and leakage reactance 4. If the supply frequency in a transformer is doubled a) Hysteresis loss also doubles b) Eddy current loss also doubles c) Iron losses double d) copper losses double Ans: a) Hysteresis loss also doubles. 5. When load on a transformer is decreased ___________ loss is decreased COPPER 6. The maximum efficiency of a transformer will occur, when ____________________ COPPER LOSS= IRON LOSS. 7. The e.m.f induced in a transformer depends on a) Frequency b) Number of turns c) Maximum value of Flux d) All the above Ans: d) All the above. 8. The principle of statically induced e.m.f is utilized in a) Transformer c) Generator Ans: a) Transformer. b) Motor d) Battery 9. A separately excited d.c. generator is not used because ______ a) it is costly b) separate d.c. source is required for field circuit c) voltage drops considerably with load d) none of the above Ans: b) separate d.c. source is required for field circuit. 10. The leakage flux in a transformer depends upon LOAD CURRENT. ________________ 11. The transformer core is usually made of FERRO MAGNETIC ___________________material. 12. The iron core is used to ______________ of the transformer. a) Increase weight b) provide tight magnetic coupling c) reduce core losses d) none of these Ans: a) provide tight magnetic oupling. 13. E.M.F equation of transformer is πΈ = 4.44ππβ π ________________ 14. Efficiency of a transformer is ππππππ ππππππ + πΏππππΈπ _______________ 15. A transformer has an efficiency of 80% and works at 100V, 4kW. If the secondary voltage is 240V. The primary current is a) 40A b) 30A c) 20A d) 10A Ans: a) 40A
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