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ELECTRICIAN TRADE THEORY SEMESTER- III Time:-1.5Hrs Marks:-75 Note :- Attempt All Question. All question carry equal marks. CHOOSE THE CORRECT ANSWER. 1. The magnetic field produced in the stator of a three phase induction motor travels at …….. A. rotating speed B. asynchronous speed C. synchronous speed D. slip speed. 2. In an induction motor the fractional slip(S) is indicated by the expression…….. A. S= (Nr-Ns)/Ns B. S= (Ns-Nr)/Ns C. S= (Nr-Ns)/Nr D. S= (Ns-Nr)/Nr 3. The fractional slip of an induction motor having a synchronous speed of 25 rev/s and a rotor speed of 23.75 rev/s is …. A. 0.05 B. 0.03 C. 0.02 D. 0.00 4. Which of the following formula is used to calculate the synchronous speed of an induction motor? A. Ns= Pxf B. Ns= 120xP/f C. Ns= 120xf/P D. Ns= fxP/120 5. A 3-phase, 400V, 50Hz induction motor has a rated speed of 715 r.p.m How many poles are there in the rotating magnetic field? A. 2 poles B. 4 poles C. 6 poles D. 8 poles 6.For a small capacity induction motor, the type of starter used is …….. A. star-delta starter B. D.O.L starter C. auto transformer starter D. step-down transformer starter. 7. The two primary parts of a squirrel cage induction motor are …………. A. rotor and stator B. stator and field C. slip rings and brush D. rotor and armature 8. When compared to the main contacts, auxiliary contacts carry ………….. A. less voltage B. higher load C. less current D. additional power, supporting main contacts. 9. An ON-OFF switch with a no-volt coil is called a ………. A. magnetic starter B. manual starter C. reversing starter D. combination starter 10. Which of the following reduces vibration, chattering, noise, wear and head in the armature of a starter magnetic core? A. shading coil B. electromagnet C. holding- circuit interlock D. centrifugal switch. 11. Thermal overload relay is provided in a starter to protect the motor against ………… A. short circuit B. open circuit C. excess current D. low voltage. 12. Line voltage of a star-connected, 3-phase circuit is 415 V. The phase voltage will be …….. A. 415 V B. 210 V C. 220 V D. 230 V 13. The phase current of a delta-connect, 3-phase circuit is 100 amps. The line current will be ……… A. 77.8A B. 100A C. 173A D. 300A 14. The approximate full load current of a 3-phase delta-connected 3 HP motor is ……. A. 4.5A B. 3.5A C. 2.5A D. 1.5A 15. Metric horse power is equal to ……… A. 746W B. 736W C. 1000W D.1730W 16. In a split-phase capacitor start induction run motor a time phase difference between the currents in the main and auxiliary windings is achieved by …….. A. placing the two windings at an angle of 180 electrical degrees in the stator slots B. applying two-phase supply across the two windings C. introducing capacitive reactance in the auxiliary winding circuit D. connecting the two windings in series across a single phase supply. 20. A capacitor start induction-run single phase motor has its capacitance replaced by an inductor of equivalent reactance value. If the motor is connected to the supply, it will ………. A. run in the reverse direction B. not start with load C. run with lower torque taking lower current D. start but will not take load 21. Universal motor gives shock because …... 17. The direction of rotation of a capacitor-stator motor can be reversed by…….. A. reversing the supply terminal connections B. reversing the connections of the auxiliary winding only C. reversing the connections of either the main winding or the auxiliary winding terminals D. reversing the connections of the main winding only. 18. The purpose of the starting capacitor in a capacitor-start induction-run motor is …. A. to increase the starting torque and decrease the starting current B. to decrease the starting torque and decrease the starting current C. to increase the starting current and increase the starting power factor D. to decrease the starting current and decrease the starting power factor. 19. Which of the following types of capacitors is preferred for the starting circuit of a single phase capacitor start induction-run motor of 2 HP rating? A. Paper capacitor of continuous rating B. Ceramic capacitor of intermittent rating C. Mica capacitor of continuous rating D. Electrolytic capacitor of intermittent rating A. short in the armature winding and poor earthing B. motor running above the normal rated speed C. applied voltage is very low D. grounded field due to weak insulation and poor earthing. 22. Motor gives humming noise when running ……. A. short circuited field coil B. loose connection in foundation bolts C. motor takes less current D. motor runs under no load. 23. Direction of rotation of universal motor can be changed …… A. by interchange the armature connections only B. by interchanging the field connections only C. by interchanging either the field or armature connection D. none of the above. 24. The slip rings are generally made up of ….. A. aluminium C. carbon B. copper D. phosphor bronze 25. A three-phase slip ring induction motorhas ……. A. a short circuit rotor C. double cage rotor B. wound rotor D. none of the above