1. With the increase in the speed of a dc motor: back emf falls and line current increases both back emf and line current falls back emf increases but the line current falls both back emf as well as line current increases 2. An electrical train employing a dc series motor is running at the fixed speed, when a sudden slight drop in the mains voltage occurs. This would result in: rise in the speed and rise in the current drop in the speed and rise in the current drop in speed with current unaltered rise in the speed and drop in the current 3. When load is removed, .......motor will run at the highest speed. cumulative - compound series shunt differential compound 4. A DC shunt motor is driving a constant torque load. On inserting an additional resistance in the armature circuit, the speed of the motor will: increases remains unchanged be zero decreases 5. The counter emf of dc motor regulates its armature voltage often exceeds the supply voltage aids the applied voltage helps in energy conversion 6. The output indicated on the name plate of any motor is always the: output power at the shaft power drawn in watts power drawn in volt amperes gross power 7. The Ta/Ia graph of a dc series motor is a straight line throughout parabola upto full load and a straight line at overloads parabola from no load to overload parabola throughout 8. The sole purpose of a commutator in a dc generator is to convert the induced ac into dc reduce sparking at brushes increase output voltage provide smoother output 9. The armature of a dc machine is made of____. soft iron silicon steel cast steel wrought iron 10. The yoke of a d.c. machine is made of ____. silicon steel cast steel soft iron aluminum 11. In a dc generator, the generator, the generated emf is directly proportional to the pole flux field current number of armature parallel paths number of dummy coils 12. The induced emf in the armature conductors of a dc motor is trapezoidal sinusoidal rectangular alternating 13. which of the following motor has the constant speed? shunt motor cumulatively compound motor series motor All of the options 14. The rotor speed of a 6 pole 50Hz induction motor is 960 r.p.m. The percentage slip is ____. 0.03 0.04 0.05 0.02 15. When the supply voltage for an induction motor is reduced by 10%, the maximum running torque will be decrease by 10% decrease by 20% increase by 10% increase by 20% 16. In Fleming's right-hand rule, the thumb point towards direction of motion of the conductor\ if fore finger point in the direction of generated e.m.f. direction of motion of conductor, if fore finger points along the lines of flux direction of induced e.m.f. direction of flux 17. In DOL starter NC(Normally closed) contact is used as start push button stop push button both start push button and stop push button none of the options 18. A dc motor can be looked upon as dc generator with the power flow reduced increased reversed modified 19. When three phase induction motor is started with star-delta starter, during normal running condition, stator is connected in star in star or delta in delta none of the options 20. The rotor of an induction motor can't run at synchronous speed, if it did so then rotor current would be zero rotor torque would be zero rotor emf would be zero all of the options 21. The advantage of Autotransformer starter over stator resistance starter is produces more torque smooth variation of speed produces less losses none of the options 22. When three phase induction motor is started with star-delta starter, during starting stator is connected in star in star or delta in delta none of the options 23. A 4 pole, 440V, 50Hz induction motor is running at a slip of 4%. The speed of motor is ____. 1560rpm 1260 rpm 1440rpm 1500rpm 24. If the input voltage and the frequency of supply is halved, to the 3-phase induction motor the maximum torque is halved the maximum torque remains the same the air-gap flux is halved none of the options 25. The torque developed by three phase induction motor is approximately proportional to double of appled voltage applied voltage square of applied voltage half of applied voltage 26. If the supply freq of an induction motor is increased by 5%, the synchronous speed will decrease by 10% increase by 5% increase by 10% decrease by 5% 27. The constant 'k' in the torque equation of a 3 phase induction motor depends supply voltage rotor current in running condition synchronous speed all of the options 28. A 4 pole, 50Hz induction motor runs at a speed of 1440rpm. The frequency of the rotor induced emf is _____. 2hz 1hz 2.5hz 3hz 29. Slip rings are usually made up of ___. phosphor-bronze copper carbon iron 30. The direction of rotation of field in a 3-ph induction motor depends upon supply freq phase sequence of supply voltage number of poles magnitude of supply voltage 31. Q. In DOL starter NO(Normally open) contact is used as stop push button start push button start push button and stop push button none of the options 32. A DC series motor is best for driving lathes shears and punches cranes and hoists machine tools 33. The value of slip is ___ at start. infinite 1 100 zero 34. When an induction motor is running at full load, rotor reactance is ------rotor resistance large compared to low comparable to very large compared to none of the options 35. When the direction of power flow in a differential compounded motor reverses, it will operate as a: differential compound generator cumulative compound generator shunt motor series motor 36. In 8 - pole wave connected motor armature, the number of parallel paths are 8 2 1 4 37. A flywheel is employed with a dc compound motor to reduce the peak demand, the compound motor should be: cumulative compound differential compound level compound none of the options 38. The direction of the armature current in a dc motor is: opposite to that of generated emf not dependent upon the direction of the armature emf the same as the generated emf none of the options 39. The maximum voltage is induced in the rotor of 3-ph induction motor when it---- runs at full load runs at no load is blocked none of the options 40. In a DC series motor increasing the load current will increase the back emf decrease the speed increase the speed better commutation 41. A 3-phase , 50 Hz , 4-pole squirrel cage induction motor has its stator rewound for 6 poles without any alternations in the rotor. The motor would now run at a speed less than 3000 rpm less than 1500 rpm zero rpm less than 1000 rpm 42. Thermal relays are used in DOL starter of Three Phase I.M. to protect the motor from high temperature protect the motor from overloading protect the motor from short circuit none of the options 43. . The coupling field electrical and mechanical systems of dc machine is____. magnetic field both electric and magnetic fields mechanical field electric field 44. If the back emf in a dc motor varnishes suddenly, then the motor: burn come to stall start hunting run at very high speeds 45. A DC series motor is best suited for electrical traction because: it runs at very high speed it is cheaper in cost it is more rugged in construction like induction motor it develops high starting torque 46. The real working part of a dc machine is the ___. armature winding commutator field winding none of the options 47. The output power of any electrical motor is taken from the: coupling mounted on the shaft field armature motor frame 48. Which of the following dc motor has maximum self relieving property: shunt differential compound cumulative compound series 49. Various methods for starting a three phase induction motor are given, which method will required six stator terminals rheostat dol auto transformer start delta 50. 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