MCQOPTIONS
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MCQOPTIONS
This section includes 657 Mcqs, each offering curated multiple-choice questions to sharpen your Testing Subject knowledge and support exam preparation. Choose a topic below to get started.
| 1. |
which mathematical expression represents correct formula to find rotor current when running at slip s.(I2r) |
| A. | e2. √(r2+x2) |
| B. | s.e2/ √(r22+x22) |
| C. | e2. √(r2+x2) |
| D. | s.e2/ √(r22+s2x22) |
| Answer» E. | |
| 2. |
A wound rotor induction motor can be distinguished from a squirrel cage induction motor by |
| A. | presence of slip-rings. |
| B. | frame size |
| C. | shaft diameter |
| D. | any of the above |
| Answer» B. frame size | |
| 3. |
The electrical equivalent of gross mechanical power developed in a dc motor is |
| A. | vil |
| B. | ebil |
| C. | ebia |
| D. | ebish |
| Answer» D. ebish | |
| 4. |
frequency( fr) of induced emf in rotor of I.M. is given by -- |
| A. | s2.f |
| B. | f2.s |
| C. | s/f |
| D. | s.f |
| Answer» E. | |
| 5. |
The starting torque of 3 phase I.M. motor is-------Supply voltage. |
| A. | independent of |
| B. | directly proportional to |
| C. | directly proportional to squre of |
| D. | none |
| Answer» D. none | |
| 6. |
If the frequency of 3-phase supply to stator of 3-phase I.M. is increased,then synchronous speed---- |
| A. | is decreased |
| B. | is increased |
| C. | remains unchanged |
| D. | none |
| Answer» C. remains unchanged | |
| 7. |
The armature winding of a dc machine is place on rotor to_____. |
| A. | save iron |
| B. | reduce losses |
| C. | improve commutation |
| D. | reduce armature reaction |
| Answer» D. reduce armature reaction | |
| 8. |
which mathematical expression represents correct formula to find rotor current (I2)during starting |
| A. | e2. √(r2+x2) |
| B. | s.e2 / √(r22+x22) |
| C. | e2/ √(r22+x22) |
| D. | s.e2. √(r2+x2) |
| Answer» D. s.e2. √(r2+x2) | |
| 9. |
When an induction motor is running at full load, rotor reactance is ------rotor resistance |
| A. | low comparable to |
| B. | very large compared to |
| C. | large compared to |
| D. | none of the above |
| Answer» B. very large compared to | |
| 10. |
If the input voltage and the frequency of supply is halved, to the 3-phase induction motor |
| A. | the maximum torque is halved |
| B. | the maximum torque remains the same |
| C. | the air-gap flux is halved |
| D. | none of these |
| Answer» B. the maximum torque remains the same | |
| 11. |
Air ducts are provided in armature core to |
| A. | increase the core area |
| B. | cool the armature |
| C. | to accommodate the windins |
| D. | none of these |
| Answer» C. to accommodate the windins | |
| 12. |
The armature conductors of 6 pole, lap wound D.C. generator are divided into |
| A. | 2 parallel paths |
| B. | 4 parallel paths |
| C. | 3 parallel paths |
| D. | 6 parallel paths |
| Answer» E. | |
| 13. |
An induction motor employs a starting device to restrict………….. at start |
| A. | line voltage |
| B. | line current |
| C. | torque |
| D. | power |
| Answer» C. torque | |
| 14. |
If number of conductors in a dc generator is Z then total number of turns are |
| A. | z |
| B. | 2z |
| C. | z/2 |
| D. | 4z |
| Answer» D. 4z | |
| 15. |
For 2 pole 50Hz I.M,sychronous speed of rotating magnetic field is---------rpm |
| A. | 3000 |
| B. | 1000 |
| C. | 1500 |
| D. | 500 |
| Answer» B. 1000 | |
| 16. |
when rotor of 3-phase I.M.motor is blocked stopped forcibly, the slip is --- |
| A. | 0 |
| B. | 0.5 |
| C. | 0.1 |
| D. | 1 |
| Answer» E. | |
| 17. |
Rotor induced emf is maximum when slip is -- |
| A. | 0 |
| B. | 1 |
| C. | 0.5 |
| D. | 0.05 |
| Answer» C. 0.5 | |
| 18. |
In iron and steel industry which motors are preferred? |
| A. | a. induction motors |
| B. | b. synchronous motors |
| C. | c. dc shunt wound motors |
| D. | d. pipe motors |
| Answer» D. d. pipe motors | |
| 19. |
A 8pole ,3 phase 50Hz I.M is running with 731.25 rpm. The slip of I.M is |
| A. | 0.0256 |
| B. | 1.975 |
| C. | 0.025 |
| D. | none of the above |
| Answer» D. none of the above | |
| 20. |
The speed of dc motor is highest on |
| A. | no load |
| B. | 70% of full load |
| C. | 10% of full load |
| D. | 100% of full load |
| Answer» B. 70% of full load | |
| 21. |
In wave winding, the number of parallel paths of armature winding is |
| A. | p |
| B. | 2 |
| C. | 4 |
| D. | p/2 |
| Answer» C. 4 | |
| 22. |
A 4-pole, 3-phase induction motor is running at 4 percent slip at full load. If the speed of the motor is 720 rpm, the supply frequency is |
| A. | 16hz |
| B. | 25hz |
| C. | 16 |
| D. | 20 |
| Answer» C. 16 | |
| 23. |
Squirrel cage I.M.motor has skewed rotor bar to help to produce constant --- . |
| A. | voltage |
| B. | torque |
| C. | frequency |
| D. | magnetic field |
| Answer» C. frequency | |
| 24. |
Synchronous speed is defined as the speed at which the |
| A. | stator magnetic field rotates. |
| B. | rotor rotates on no-load. |
| C. | rotor rotates on full load. |
| D. | none of the above. |
| Answer» B. rotor rotates on no-load. | |
| 25. |
A 4 pole, 50Hz , 3 phase I M is running at 1425rpm on full load having rotor impedance per phase on standstill as 0.4+j2Ω. If voltage between the slip rings on open circuit is 520V then the maximum torque developed is ___ Nm. |
| A. | 202.52 |
| B. | 165.53 |
| C. | 430.36 |
| D. | 514.21 |
| Answer» D. 514.21 | |
| 26. |
The speed of an induction motor |
| A. | decreases too much with the increase of load |
| B. | increase with the increase of load |
| C. | decreases slightly with the increase of load |
| D. | remains constant with the increase of load |
| Answer» D. remains constant with the increase of load | |
| 27. |
The resistance of the shunt field winding as compared to series field winding is ____. |
| A. | less |
| B. | more |
| C. | the same |
| D. | none of the above |
| Answer» C. the same | |
| 28. |
Squirrel cage I.M. motor suffers from disadvantage of -- starting torque. |
| A. | low |
| B. | high |
| C. | pulsating |
| D. | none |
| Answer» B. high | |
| 29. |
Each commutator segment is connected to armature conductor by means of ___ |
| A. | insulator |
| B. | dielectric |
| C. | copper lug |
| D. | resistance wire |
| Answer» D. resistance wire | |
| 30. |
Various methods for starting a three phase induction motor are given, which method will required six stator terminals |
| A. | dol |
| B. | auto transformer |
| C. | start delta |
| D. | rheostat |
| Answer» D. rheostat | |
| 31. |
A sinusoidal voltage of frequency 1 Hz is applied to the field of a d.c generator. The armature voltage will be |
| A. | 1 hz square wave |
| B. | 1 hz sine wave |
| C. | d. c voltage |
| D. | zero |
| Answer» C. d. c voltage | |
| 32. |
The commutator of D.C. geenrator acts as ___ |
| A. | an amplifier |
| B. | a rectifier |
| C. | a load |
| D. | none of the above |
| Answer» C. a load | |
| 33. |
A 4 pole 1500 rpm,dc generator has a lap wound armature having 24 slots with 10 conductors/slot.If flux/pole is 0.04Wb then emf generator in armature is -----V |
| A. | 480v |
| B. | 240v |
| C. | 960v |
| D. | 120v |
| Answer» C. 960v | |
| 34. |
A 4 pole, 250V series motor has a wave connected armature with 1254 conductors. The flux per pole is 22mWb when the motor taking 50A. Iron and friction lossses amount to 1000W. Armature resistance 0.2Ω, series field resistance 0.2Ω. What is the speed of the motor___. |
| A. | 200rpm |
| B. | 225rpm |
| C. | 175rpm |
| D. | 250rpm |
| Answer» E. | |
| 35. |
A 8 pole ,50Hz ,3phase I.M ,If full load slip is 2.5%. Rotor speed is |
| A. | 200 |
| B. | 731 |
| C. | 600 |
| D. | 1000 |
| Answer» C. 600 | |
| 36. |
For I.M. running with 970rpm with slip of 3%, the synchronous speed of rotating magnetic field |
| A. | 750 |
| B. | 1000 |
| C. | 1500 |
| D. | 500 |
| Answer» C. 1500 | |
| 37. |
A 4 pole, 440V, 50Hz induction motor is running at a slip of 4%. The speed of motor is ____. |
| A. | 1260 rpm |
| B. | 1440rpm |
| C. | 1500rpm |
| D. | 1560rpm |
| Answer» C. 1500rpm | |
| 38. |
The shaft torque in a DC motor is less than total armature torque because of ____in the motor |
| A. | cu losses |
| B. | field losses |
| C. | iron and friction lossees |
| D. | none of the above |
| Answer» D. none of the above | |
| 39. |
The speed of rotating field due to rotor currents relative to rotor surface in an induction motor is |
| A. | n |
| B. | s.n |
| C. | ns |
| D. | s.ns |
| Answer» C. ns | |
| 40. |
A shunt motor runs at 500rpm on a 200V circuit. Its armature resistance is 0.5Ω and the current taken is 30A in addition to field current. What resistance must be placed in series with armature circuit to reduce to speed to 300 rpm; the current in armature remains same. |
| A. | 4.24Ω |
| B. | 3.78Ω |
| C. | 6.74Ω |
| D. | 2.47Ω |
| Answer» E. | |
| 41. |
Excessive sparking at the brushes may be caused due to _____. |
| A. | dirt on the commutator |
| B. | loose coupling |
| C. | misalignment of machine |
| D. | worn bearing |
| Answer» B. loose coupling | |
| 42. |
A 4 pole 1200 rpm, dc generator has lap wound armature producing 240v emf in the armature with flux/pole as 0.02Wb,then total number of armature conductors are |
| A. | 2400 |
| B. | 1000 |
| C. | 600 |
| D. | 1200 |
| Answer» D. 1200 | |
| 43. |
____ motor is a variable speed motor. |
| A. | series |
| B. | shunt |
| C. | cumulatively compounded |
| D. | differetial compounded |
| Answer» B. shunt | |
| 44. |
In a 240v dc motor, back emf is 220v and Ra= 0.5Ω then its armature current is |
| A. | 20a |
| B. | 10a |
| C. | 80a |
| D. | 40a |
| Answer» E. | |
| 45. |
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 |
| A. | less than 1000 rpm |
| B. | less than 1500 rpm |
| C. | less than 3000 rpm |
| D. | zero rpm |
| Answer» B. less than 1500 rpm | |
| 46. |
For 3phase I.M,the synchronous speed of rotating magnetic field is 750 rpm, speed of rotor is 731.25 rpm ,then slip is |
| A. | 0.025 |
| B. | 0.06 |
| C. | 0.03 |
| D. | 0.04 |
| Answer» B. 0.06 | |
| 47. |
A 3-phase ,400 V, 4-pole induction motor is fed from a 3-phase, 400V, 50 Hz supply and runs at 1440 rpm. The frequency of rotor emf is |
| A. | 2hz |
| B. | 50hz |
| C. | 4hz |
| D. | 0hz |
| Answer» B. 50hz | |
| 48. |
For 6 pole 50Hz I.M, sychronous speed of rotating magnetic field is--------- |
| A. | 1200rpm |
| B. | 1000rpm |
| C. | 500rpm |
| D. | 50rpm |
| Answer» C. 500rpm | |
| 49. |
A 4 pole, 50Hz , 3 phase I M is running at 1425rpm on full load having rotor impedance per phase on standstill as 0.4+j2Ω. The external resistance required in the rotor per phase to get maximum torque at start is ___. |
| A. | 0.2 |
| B. | 1.6 |
| C. | 0.8 |
| D. | 0.4 |
| Answer» C. 0.8 | |
| 50. |
the direction of rotating magnetic field depends upon |
| A. | the direction of rotating magnetic field depends upon |
| B. | phase sequence of supply voltage |
| C. | supply current |
| D. | supply voltage |
| Answer» C. supply current | |