Unit-3 Single Phase Transformers & Electrostatics

1. A transformer transformsa. frequency b. voltage c. current d. voltage and current2. In a transformer electrical power is transformed from one circuit to another without change in the_____________a. Voltage b. current c. frequency d. none of these3. A Transformer works on the principle of ______a. Faradays Law b. Mutual induction c. Self induction d. Superposition4. The primary and secondary windings of a transformer are_______ coupled each othera. Electrically b. magnetically c. electrically & magnetically d. none of these5. Which of the following is not a basic element of a transformer?a. Core b. primary winding c. secondary winding d. mutual flux6. In an ideal transformera. winding have no resistance b. core has no losses c. core has infinite permeability d. all of the above.7. The main purpose of using core in a transformer is to a. decrease iron losses b. prevent eddy current losses c. eliminate magnetic hysteresis d. decrease reluctance of common magnetic circuit.8. Transformer core are laminated in order to a. simplifies its construction b. minimize eddy current loss c. reduce cost d. reduces hysteresis loss.9. 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 turns should bea. 1600 b. 250 c. 400 d.125010. A step up transformer increasesa. voltage b. current c. power d. frequency11. The primary and secondary winding of an ordinary 2-winding transformer always havea. different number of turns. b. same size of copper wirec. a common magnetic circuit d. separate magnetic circuit.12. In a transformer, the leakage flux of each winding is proportional to the current in that winding becausea. ohms law applies to the magnetic circuits b. leakage paths do not saturate c. the two windings are electrically isolated d. mutual flux is confined to the core.13. In relation to a transformer, the ratio 20:1 indicates thata. there are 20 turns on primary one turn on secondary b. secondary voltage is 1/20th of primary voltage c. primary current is 20 times greater than the secondary current d. for every 20 turns on primary, there is one turn on secondary.14. A transformer has negative voltage regulation when its load factor isa. zero b. unity c. leading d. lagging.15. Transformers are rated in KVA instead of KW becausea. load power factor is often not known b. KVA is fixed whereas KW depends on load p .f. c. total transformer loss depends on volt ampere d. it has become customary16. A transformer actually transforms a. voltage. b. magnetic field lines. c. generators into motors. d. non-safe forms of energy to safe forms of energy.17. Transformers use ac so there will be the required a. transfer of energy from coil to coil. b. voltage for transformation. c. change in magnetic field for operation. d. change in input current.18. Electric power can be transmitted from one place to another without the need for connecting wires in between. this statement is a. true. b. false. c. both true d. none of these19. A step-up transformer increases a. power. b. energy. c. both of these d. neither of these20. The principal advantage of ac power over dc power is that a. less energy is dissipated during transmission. b. ac voltage oscillates while dc voltage does not. c. ac voltage can be transformed via conventional transformers. d. ac circuits multiply power more easily. 21. A step-up transformer has a ratio of 1 to 10. neglecting slight losses, if 100 w of power go into the Primary coil, the power coming from the secondary coil is a. 1 w. b. 10 w. c. 100 w. d. 1000 w.22. The voltage across the input terminals of a transformer is 110 v. the primary has 50 loops and the secondary has 25 loops. the voltage the transformer puts out is a. 25 v. b. 55 v. c. 110 v. d. 220 v. 23. Four amps of current exist in the primary coil of a transformer. the voltage across the primary coil is 110 v. what is the power output of the secondary coil? a. 27.5 w b. 110 w c. 440 w d. 880 w24. A certain transformer doubles input voltage. if the primary coil has 10 amp of current, then the current in the secondary coil is a. 2 a. b. 5 a. c. 10 a. d. 25 a.25. A transformer has secondary full load current of 10 amp and secondary no load induced emf of 200v then its kva rating is a. 2000 b. 200 c.2 d. 2026. Which loss is variable loss in transformer?a. eddy current loss. b. copper c. hysteresis. d friction27. A transformer has 200 w iron loss at its full load . then iron loss at half full load a. 100w b. 200w c. 400w d. 300w28. The full load copper loss for transformer is 800w then the copper loss at half the full load a. 200w b.800w c. 400w d. 1600w29. When the turns ratio of a transformer is 20 and the primary ac voltage is 12v ,the secondary voltage is a. 12v b. 120v. c.240v. d.2400v30. If Cu loss of a transformer at 7/8 th full load is 4900 W,then its full load copper loss would be _____watta. 5600 b. 6400 c. 375 d. 42931. In of transformer, the coils can be easily removed from maintenance point of view.a. Berry type b. core type c. shell type d. none of these