MCQOPTIONS
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MCQOPTIONS
This section includes 132 Mcqs, each offering curated multiple-choice questions to sharpen your Electrical Machines knowledge and support exam preparation. Choose a topic below to get started.
| 1. |
For a dc machine, its commutator has a diameter of 50 c rotating at 1000 rpm. For a brush width of 1 cm, the time commutation taken by the machine will be _________ |
| A. | 0.382 ms |
| B. | 0.456 ms |
| C. | 0.573 ms |
| D. | 0.312 ms |
| Answer» B. 0.456 ms | |
| 2. |
A dc machine is run at rated speed in forward direction and then in backward direction. It is observed that, speeds of the rotation are different, then it leads to the conclusion of _________ |
| A. | incorrect brush placement |
| B. | incorrect pole and core alignment |
| C. | incorrect field supply |
| D. | all of the mentioned |
| Answer» B. incorrect pole and core alignment | |
| 3. |
If the students give a forward shift of 10° to the dc generator, then it _________ |
| A. | reduces flux per pole |
| B. | improves flux per pole |
| C. | increases the flux density in core |
| D. | none of the mentioned |
| Answer» B. improves flux per pole | |
| 4. |
The post effects of the armature reaction is _________ |
| A. | main field distortion |
| B. | shift in MNA |
| C. | reduction in main field |
| D. | none of the mentioned |
| Answer» E. | |
| 5. |
The effect of fringing increases as we _________ |
| A. | increase air gap |
| B. | decrease air gap |
| C. | increase in flux density |
| D. | introduce more ferric core material |
| Answer» B. decrease air gap | |
| 6. |
Thyristor controlled starter is preferred over DOL starter due to _________ |
| A. | lesser losses |
| B. | controlled direction |
| C. | least resistance offered |
| D. | all of the mentioned |
| Answer» B. controlled direction | |
| 7. |
The shunt motor starters that can be used is/are ___________ |
| A. | 3-point and 4-point starter |
| B. | 5-point starter |
| C. | 4-point starter |
| D. | 5-point and 3-point starter |
| Answer» B. 5-point starter | |
| 8. |
Considering a human handed control system for the dc motor speed control, if the resistance wire cut out too slowly, then the _____________ |
| A. | starting resistance would burn |
| B. | field winding would burn |
| C. | speed will rise steeply |
| D. | any of the mentioned |
| Answer» B. field winding would burn | |
| 9. |
A dc series motor of resistance 1 Ω across terminals runs at 1000 rpm at 250 V taking a current of 20 A. When an additional resistance of 6 Ω is inserted in series and taking the same current, the new speed would be |
| A. | 142.8 rpm |
| B. | 166.7 rpm |
| C. | 478.3 rpm |
| D. | 956.6 rpm |
| Answer» D. 956.6 rpm | |
| 10. |
Identify the important feature of a DC series motor. |
| A. | Low starting torque |
| B. | Zero starting torque |
| C. | Medium starting torque |
| D. | High starting torque |
| Answer» E. | |
| 11. |
E0 = no load induced e.m.fIf = field currentIa = armature currentE = generated e.m.f. on loadV = terminal voltageI = load currentMatch the characteristics with its relevant relation.List – I (Characteristic)List – II (Relation) A. Open circuit characteristics 1. V v.If B. Internal characteristics 2. E0 v.If C. External characteristics 3. E v.Ia D. Load saturation curve 4. V v.I |
| A. | A - 4, B - 3, C - 2, D - 1 |
| B. | A - 2, B - 1, C - 4, D - 3 |
| C. | A - 4, B - 1, C - 2, D - 3 |
| D. | A - 2, B - 3, C - 4, D - 1 |
| Answer» E. | |
| 12. |
A 300 V dc shunt motor draws a line current of 51 A. The armature and the field resistances are 32 mΩ and 300 Ω respectively. Assuming 1 HP = 746 W, the mechanical power developed by the motor is |
| A. | 20 HP |
| B. | 20.1 HP |
| C. | 20.4 HP |
| D. | 20.5 HP |
| Answer» B. 20.1 HP | |
| 13. |
How can we find the applications of Differential compound D.C. motors? |
| A. | zero torque |
| B. | armature resistance |
| C. | constant speed |
| D. | low starting torque |
| Answer» E. | |
| 14. |
Find the supply current in a DC shunt motor where the field resistance is 200 ohm, armature resistance is 2 ohm, supply voltage is 100 V and speed is 500 rpm. Back emf constant is 0.18 V per rpm |
| A. | 50 A |
| B. | 50.5 A |
| C. | 5.5 A |
| D. | 0.5 A |
| Answer» D. 0.5 A | |
| 15. |
A faceplate starter is used to start |
| A. | Induction motor |
| B. | Universal motor |
| C. | Synchronous motor |
| D. | DC series motor |
| Answer» E. | |
| 16. |
Commutator is used in |
| A. | Single phase induction motor |
| B. | Three phase induction motor |
| C. | DC motor |
| D. | Brush less DC motor |
| Answer» D. Brush less DC motor | |
| 17. |
During regenerative braking the motor operates as: |
| A. | Motor |
| B. | Inverter |
| C. | Transformer |
| D. | Generator |
| Answer» E. | |
| 18. |
An electric motor is developing 10 kW at a speed of 900 rpm. The torque available at the shaft is |
| A. | 106 N-m |
| B. | 1.7 N-m |
| C. | 10,000 N-m |
| D. | 450 N-m |
| Answer» B. 1.7 N-m | |
| 19. |
An electric motor with “constant output power” will have a torque speed characteristics in the form of a |
| A. | Straight line through the origin |
| B. | Straight line parallel to speed axis |
| C. | Circle about the origin |
| D. | Rectangular hyperbola |
| Answer» E. | |
| 20. |
Hopkinson’s test for D.C. motors is conducted of: |
| A. | Low Load |
| B. | Half Load |
| C. | Full Load |
| D. | No Load |
| Answer» D. No Load | |
| 21. |
Overheating of DC motors is mainly due to: |
| A. | Rough commutator |
| B. | Overloads |
| C. | Loose parts |
| D. | Absence of brushes |
| Answer» C. Loose parts | |
| 22. |
If the flux of a dc motor approached zero __________ |
| A. | its speed will approach zero |
| B. | the motor will tend to run at infinite speed |
| C. | the motor will stop |
| D. | its speed will remain unchanged |
| Answer» C. the motor will stop | |
| 23. |
It is advisable to start a DC series motor with some load to: |
| A. | avoid sparking |
| B. | limit the speed |
| C. | limit the flux |
| D. | limit the current |
| Answer» C. limit the flux | |
| 24. |
A shunt motor supplied at 250 V, runs at 900 rpm and the armature current drawn is 30 A. The resistance of the armature circuit is 0.4 Ω. The resistance required in series with the armature to reduce the speed to 600 rpm when the armature current is 20 A will be |
| A. | 3.17 Ω |
| B. | 2.17 Ω |
| C. | 5.17 Ω |
| D. | 4.17 Ω |
| Answer» E. | |
| 25. |
In electric braking of shunt motors, plugging is used to control.1. Printing press2. Rolling mills3. ElevatorsThe incorrect amongst these is / are: |
| A. | Only 3 |
| B. | 1 and 2 |
| C. | None of the other options |
| D. | 2 and 3 |
| Answer» D. 2 and 3 | |
| 26. |
A 200 V separately excited DC motor has an armature resistance of 0.05 draws an armature current of 20 A, running at 1,200 rpm. Calculate the approximate torque developed for given armature current. |
| A. | π/200 Nm |
| B. | 10/4 Nm |
| C. | 100/π Nm |
| D. | π/100 Nm |
| Answer» D. π/100 Nm | |
| 27. |
In DC shunt motor if load is increased, then speed will |
| A. | Increased slightly |
| B. | Reduce slightly |
| C. | Remains constant |
| D. | Increase proportional |
| Answer» C. Remains constant | |
| 28. |
In a DC motor, constant torque is produced due to |
| A. | Rotor laminations |
| B. | End plates |
| C. | Pole shoes |
| D. | Commutator |
| Answer» E. | |
| 29. |
In a DC shunt motor, the torque produced is proportional to: |
| A. | Armature current |
| B. | (Armature current)2 |
| C. | Ampere-turn |
| D. | (Ampere-turn)2 |
| Answer» B. (Armature current)2 | |
| 30. |
Motor used for punching machine is subjected to |
| A. | No load |
| B. | Continuous part load |
| C. | Continuous full load |
| D. | Intermittent load |
| Answer» E. | |
| 31. |
A 4 point starter is used to start and control the speed of a |
| A. | DC shunt motor with armature resistance control |
| B. | DC shunt motor with field weakening control |
| C. | DC series motor |
| D. | DC compound motor |
| Answer» C. DC series motor | |
| 32. |
One of the main advantage of Swinburne’s test is that it, |
| A. | is applicable both to shunt and compound motors |
| B. | needs one running test |
| C. | is very economical and convenient |
| D. | ignores any change in iron loss |
| Answer» D. ignores any change in iron loss | |
| 33. |
A field test is performed on which type of DC motor? |
| A. | Shunt motor |
| B. | Short shunt motor |
| C. | Separately excited motor |
| D. | Series motor |
| Answer» E. | |
| 34. |
If the applied voltage to a dc machine is 230 V, then the back emf, for maximum power developed is |
| A. | 115 V |
| B. | 200 V |
| C. | 230 V |
| D. | 460 V |
| Answer» B. 200 V | |
| 35. |
A D.C shunt motor is found suitable to drive fans because they require: |
| A. | Small torque at start up |
| B. | Large torque at high speeds |
| C. | Practically constant voltage |
| D. | Small torque at start up as well as practically constant voltage |
| Answer» E. | |
| 36. |
_____ is required for the motor to remain uniform to the surface and to avoid ridge formation. |
| A. | Brush clearance |
| B. | Brush angle |
| C. | Brush spacing |
| D. | Brush staggering |
| Answer» E. | |
| 37. |
A DC shunt generator has a speed of 800 rpm when delivering 20 A to the load at the terminal voltage of 220 V. If the same machine is run as a motor it takes a line current of 20 A from 220 V supply. The speed of the machine as a motor will be |
| A. | 800 rpm |
| B. | More than 800 rpm |
| C. | Less than 800 rpm |
| D. | Both higher or lower than 800 rpm |
| Answer» B. More than 800 rpm | |
| 38. |
A DC series motor is best suited for driving |
| A. | Lathes |
| B. | Cranes and hoists |
| C. | Shears and punches |
| D. | Machine tools |
| Answer» C. Shears and punches | |
| 39. |
In case of dc shunt motors, the regenerative braking is employed when the load _________. |
| A. | has an overhauling characteristic |
| B. | is variable |
| C. | is constant |
| D. | also acts as braking force |
| Answer» B. is variable | |
| 40. |
In a dc motor, the commutation is used to: |
| A. | Convert dc current from armature conductor to ac current feedback to supply |
| B. | Convert ac current from armature conductor to dc current feedback to supply |
| C. | Convert dc current from supply to ac current in armature conductor |
| D. | covert ac current from supply to dc current in armature conductor |
| Answer» D. covert ac current from supply to dc current in armature conductor | |
| 41. |
A 15 KW, 230 V dc shunt motor has armature circuit, resistance of 0.4 Ω and field circuit resistance of 230 Ω. At no load and rated voltage, the motor runs at 1440 rpm and the line current drawn by the motor is 5 A. At full load, the motor draws a line current of 70 A. Neglect armature reaction. The full load speed of the motor in rpm |
| A. | 1000 |
| B. | 1080 |
| C. | 1240 |
| D. | 1340 |
| Answer» D. 1340 | |
| 42. |
DC Series motors are considered most suitable for the application in: |
| A. | Fans |
| B. | Water Pumps |
| C. | Traction |
| D. | Flour-mills |
| Answer» D. Flour-mills | |
| 43. |
A 3- point starter is used to: |
| A. | Minimize back emf |
| B. | Minimize armature current |
| C. | Maximize armature current |
| D. | Maximize back emf |
| Answer» C. Maximize armature current | |
| 44. |
Directions: It consists of two statements, one labelled as the ‘Statement (I)’ and the other as ‘Statement (II)’. You are to examine these two statements carefully and select the answer using the codes given below:Statement (I): The direct-on-line (DOL) starter is used to start a small dc motor.Statement (II): DOL starter limits initial current drawn by the armature circuit. |
| A. | Both Statement (I) and Statement (II) are individually true and Statement (II) is the correct explanation of Statement (I) |
| B. | Both Statement (I) and Statement (II) are individually true but Statement (II) is NOT the correct explanation of Statement (I) |
| C. | Statement (I) is true but Statement (II) is false |
| D. | Statement (I) is false but Statement (II) is true |
| Answer» D. Statement (I) is false but Statement (II) is true | |
| 45. |
A separately excited dc generator having armature resistance of 0.1 Ω supplies 4 kW at a terminal voltage of 200 V. If the machine is now operated as a motor at the same terminal voltage and the same armature current with the flux/pole being increased by 10%, the ratio of the generator speed to the motor speed will approximately be |
| A. | 0.09 |
| B. | 0.11 |
| C. | 1.04 |
| D. | 1.12 |
| Answer» E. | |
| 46. |
At certain loading conditions, back e.m.f. in DC motor was found half of the supply voltage. Then power delivered by DC motor is |
| A. | half of the rated power |
| B. | maximum |
| C. | minimum |
| D. | double of the rated power |
| Answer» C. minimum | |
| 47. |
A speed of a dc motor is |
| A. | Directly proportional to back emf and inversely proportional to flux |
| B. | Inversely proportional to back emf and directly proportional to flux |
| C. | Directly proportional to back emf as well as to flux |
| D. | Inversely proportional to back emf as well as to flux |
| Answer» B. Inversely proportional to back emf and directly proportional to flux | |
| 48. |
For constant speed operation, the most suitable DC motor used is: |
| A. | Synchronous motor |
| B. | DC series motor |
| C. | Separately excited DC motor |
| D. | DC shunt motor |
| Answer» E. | |
| 49. |
______ is a heteropolar structure with stationary poles and a rotating armature. |
| A. | A DC machine |
| B. | A three-phase synchronous motor |
| C. | A single-phase induction motor |
| D. | A three-phase induction motor |
| Answer» B. A three-phase synchronous motor | |
| 50. |
Determine the speed control method for a DC motor shown in the following figure |
| A. | Field diverter method |
| B. | Armature diverter method |
| C. | Tapped Field Control |
| D. | Resistance diverter control |
| Answer» B. Armature diverter method | |