McqMate
These multiple-choice questions (MCQs) are designed to enhance your knowledge and understanding in the following areas: Electrical Engineering .
Chapters
| 1. |
No-load speed of which of the following motor will be highest ? |
| A. | Shunt motor |
| B. | Series motor |
| C. | Cumulative compound motor |
| D. | Differentiate compound motor |
| Answer» B. Series motor | |
| 2. |
The direction of rotation of a D.C. series motor can be changed by |
| A. | interchanging supply terminals |
| B. | interchanging field terminals |
| C. | either of (a) and (b) above |
| D. | None of the above |
| Answer» B. interchanging field terminals | |
| 3. |
Which of the following application requires high starting torque ? |
| A. | Lathe machine |
| B. | Centrifugal pump |
| C. | Locomotive |
| D. | Air blower |
| Answer» C. Locomotive | |
| 4. |
If a D.C. motor is to be selected for conveyors, which rriotor would be preferred ? |
| A. | Series motor |
| B. | Shunt motor |
| C. | Differentially compound motor |
| D. | Cumulative compound motor |
| Answer» A. Series motor | |
| 5. |
Which D.C. motor will be preferred for machine tools ? |
| A. | Series motor |
| B. | Shunt motor |
| C. | Cumulative compound motor |
| D. | Differential compound motor |
| Answer» B. Shunt motor | |
| 6. |
Differentially compound D.C. motors can find applicationsrequiring |
| A. | high starting torque |
| B. | low starting torque |
| C. | variable speed |
| D. | frequent on-off cycles |
| Answer» B. low starting torque | |
| 7. |
Which D.C. motor is preferred for elevators ? |
| A. | Shunt motor |
| B. | Series motor |
| C. | Differential compound motor |
| D. | Cumulative compound motor |
| Answer» D. Cumulative compound motor | |
| 8. |
If the field of a D.C. shunt motor gets opened while motor is running |
| A. | the speed of motor will be reduced % |
| B. | the armature current will reduce |
| C. | the motor will attain dangerously high speed 1 |
| D. | the motor will continue to nuvat constantspeed |
| Answer» C. the motor will attain dangerously high speed 1 | |
| 9. |
Starters are used with D.C. motors because |
| A. | these motors have high starting torque |
| B. | these motors are not self-starting |
| C. | back e.m.f. of these motors is zero initially |
| D. | to restrict armature current as there is no back e.m.f. whilestarting |
| Answer» D. to restrict armature current as there is no back e.m.f. whilestarting | |
| 10. |
In D.C. shunt motors as load is reduced |
| A. | the speed will increase abruptly |
| B. | the speed will increase in proportion to reduction in load |
| C. | the speed will remain almost/constant |
| D. | the speed will reduce |
| Answer» C. the speed will remain almost/constant | |
| 11. |
A D.C. series motor is that which |
| A. | has its field winding consisting of thick wire and lessturns |
| B. | has a poor torque |
| C. | can be started easily without load |
| D. | has almost constant speed |
| Answer» A. has its field winding consisting of thick wire and lessturns | |
| 12. |
For starting a D.C. motor a starter is required because |
| A. | it limits the speed of the motor |
| B. | it limits the starting current to a safe value |
| C. | it starts the motor |
| D. | none of the above |
| Answer» B. it limits the starting current to a safe value | |
| 13. |
The type of D.C. motor used for shears and punches is |
| A. | shunt motor |
| B. | series motor |
| C. | differential compoutid D.C. motor |
| D. | cumulative compound D.C. motor |
| Answer» D. cumulative compound D.C. motor | |
| 14. |
If a D.C. motor is connected across the A.C. supply it will |
| A. | run at normal speed |
| B. | not run |
| C. | run at lower speed |
| D. | burn due to heat produced in the field winding by .eddy currents |
| Answer» D. burn due to heat produced in the field winding by .eddy currents | |
| 15. |
To get the speed of D.C, motor below the normal without wastage of electrical energy is used. |
| A. | Ward Leonard control |
| B. | rheostatic control |
| C. | any of the above method |
| D. | none of the above method |
| Answer» A. Ward Leonard control | |
| 16. |
When two D.C. series motors are connected in parallel, the resultant speed is |
| A. | more than the normal speed |
| B. | loss than the normal speed |
| C. | normal speed |
| D. | zero |
| Answer» C. normal speed | |
| 17. |
The speed of a D.C. shunt motor more than its full-load speed can be obtained by |
| A. | decreasing the field current |
| B. | increasing the field current |
| C. | decreasing the armature current |
| D. | increasing the armature current |
| Answer» A. decreasing the field current | |
| 18. |
In a D.C. shunt motor, speed is |
| A. | independent of armature current |
| B. | directly proportional to the armature current |
| C. | proportional to the square of the current |
| D. | inversely proportional to the armature current |
| Answer» A. independent of armature current | |
| 19. |
A direct on line starter is used: for starting motors |
| A. | iip to 5 H.P. |
| B. | up to 10 H.P. |
| C. | up to 15 H.P. |
| D. | up to 20 H.P. |
| Answer» A. iip to 5 H.P. | |
| 20. |
What will happen if the back e.m.f. of a D.C. motor vanishes suddenly? |
| A. | The motor will stop |
| B. | The motor will continue to run |
| C. | The armature may burn |
| D. | The motor will run noisy |
| Answer» C. The armature may burn | |
| 21. |
In case of D.C. shunt motors the speed is dependent on back e.m.f. only because |
| A. | back e.m.f. is equal to armature drop |
| B. | armature drop is negligible |
| C. | flux is proportional to armature current |
| D. | flux is practically constant in D:C. shuntmotors |
| Answer» D. flux is practically constant in D:C. shuntmotors | |
| 22. |
In a D.C. shunt motor, under the conditions of maximum power, the current inthe armature will be |
| A. | almost negligible |
| B. | rated full-load current |
| C. | less than full-load current |
| D. | more than full-load current |
| Answer» D. more than full-load current | |
| 23. |
These days D.C. motors are widely used in |
| A. | pumping sets |
| B. | air compressors |
| C. | electric traction |
| D. | machine shops |
| Answer» C. electric traction | |
| 24. |
By looking at which part of the motor, it can be easily confirmedthat a particular motor is D.C. motor? |
| A. | Frame |
| B. | Shaft |
| C. | Commutator |
| D. | Stator |
| Answer» C. Commutator | |
| 25. |
In which of the following applications D.C. series motor is invariably tried? |
| A. | Starter for a car |
| B. | Drive for a water pump |
| C. | Fan motor |
| D. | Motor operation in A.C. or D.C. |
| Answer» A. Starter for a car | |
| 26. |
In D.C. machines fractional pitch winding is used |
| A. | to improve cooling |
| B. | to reduce copper losses |
| C. | to increase the generated e.m.f. |
| D. | to reduce the sparking |
| Answer» D. to reduce the sparking | |
| 27. |
A three point starter is considered suitable for |
| A. | shunt motors |
| B. | shunt as well as compound motors |
| C. | shunt, compound and series motors |
| D. | all D.C. motors |
| Answer» B. shunt as well as compound motors | |
| 28. |
In case-the conditions for maximum power for a D.C. motor are established,the efficiency of the motor will be |
| A. | 100% |
| B. | around 90% |
| C. | anywhere between 75% and 90% |
| D. | less than 50% |
| Answer» D. less than 50% | |
| 29. |
The ratio of starting torque to full-load torque is least in case of |
| A. | series motors |
| B. | shunt motors |
| C. | compound motors |
| D. | none of the above |
| Answer» B. shunt motors | |
| 30. |
In D.C. motor which of the following can sustain the maximum temperature rise? |
| A. | Slip rings |
| B. | Commutator |
| C. | Field winding |
| D. | Armature winding |
| Answer» C. Field winding | |
| 31. |
Which of the following law/rule can he used to determine the direction of rotationof D.C. motor ? |
| A. | Lenz's law |
| B. | Faraday's law |
| C. | Coloumb'slaw |
| D. | Fleming's left-hand rule |
| Answer» D. Fleming's left-hand rule | |
| 32. |
Which of the following load normally needs starting torque more than therated torque? |
| A. | Blowers |
| B. | Conveyors |
| C. | Air compressors |
| D. | Centrifugal pumps |
| Answer» B. Conveyors | |
| 33. |
The starting resistance of a D.C. motor is generally |
| A. | low |
| B. | around 500 Q |
| C. | 1000 Q |
| D. | infinitely large |
| Answer» A. low | |
| 34. |
The speed of a D.C. series motor is |
| A. | proportional to the armature current |
| B. | proportional to the square of the armature current |
| C. | proportional to field current |
| D. | inversely proportional to the armature current |
| Answer» D. inversely proportional to the armature current | |
| 35. |
In a D.C. series motor, if the armature current is reduced by 50%, the torque of the motor will be equal to |
| A. | 100% of the previous value |
| B. | 50% of the previous value |
| C. | 25% of the previous value |
| D. | 10% of the previous value |
| Answer» C. 25% of the previous value | |
| 36. |
The current drawn by the armature of D.C. motor is directly proportional to |
| A. | the torque required |
| B. | the speed of the motor |
| C. | the voltage across the terminals |
| D. | none of the above |
| Answer» A. the torque required | |
| 37. |
The power mentioned on the name plate of an electric motor indicates |
| A. | the power drawn in kW |
| B. | the power drawn in kVA |
| C. | the gross power |
| D. | the output power available at the shaft |
| Answer» D. the output power available at the shaft | |
| 38. |
Which D.C. motor has got maximum self loading property? |
| A. | Series motor |
| B. | Shunt motor |
| C. | Cumulatively compounded 'motor |
| D. | Differentially compounded motor |
| Answer» D. Differentially compounded motor | |
| 39. |
Which D.C. motor will be suitable alongwith flywheel for intermittent light andheavy loads? |
| A. | Series motor |
| B. | Shunt motor |
| C. | Cumulatively compounded motor |
| D. | Differentially compounded motor |
| Answer» C. Cumulatively compounded motor | |
| 40. |
If a D.C. shunt motor is working at no load and if shunt field circuit suddenly opens |
| A. | nothing will happen to th£ motor |
| B. | this will make armature to take heavy current, possibly burning it |
| C. | this will result in excessive speed, possibly destroying armature due to excessive centrifugal stresses |
| D. | motor will run at very slow speed |
| Answer» C. this will result in excessive speed, possibly destroying armature due to excessive centrifugal stresses | |
| 41. |
D.C. series motors are used |
| A. | where load is constant |
| B. | where load changes frequently |
| C. | where constant operating speed is needed |
| D. | in none of the above situations. |
| Answer» D. in none of the above situations. | |
| 42. |
For the same H.P. rating and full load speed, following motor has poor starting torque |
| A. | shunt |
| B. | series |
| C. | differentially compounded |
| D. | cumulativelyc'ompounded |
| Answer» C. differentially compounded | |
| 43. |
In case of conductively compensated D.C. series motors, the compensating winding is provided |
| A. | as separately wound unit |
| B. | in parallel with armature winding |
| C. | in series with armature winding |
| D. | in parallel with field winding |
| Answer» C. in series with armature winding | |
| 44. |
Sparking at the commutator of a D.C. motor may result in |
| A. | damage to commutator segments |
| B. | damage to commutator insulation |
| C. | increased power consumption |
| D. | all of the above |
| Answer» D. all of the above | |
| 45. |
Which of the following motor is preferred for operation in highly explosive atmosphere ? |
| A. | Series motor |
| B. | Shunt motor |
| C. | Air motor |
| D. | Battery operated motor |
| Answer» C. Air motor | |
| 46. |
If the supply voltage for a D.C. motor is increased, which of the following willdecrease ? |
| A. | Starting torque |
| B. | Operating speed |
| C. | Full-load current |
| D. | All of the above |
| Answer» C. Full-load current | |
| 47. |
Which one of the following is not the function of pole shoes in a D.C. machine ? |
| A. | To reduce eddy current loss |
| B. | To support the field coils |
| C. | To spread out flux for better unifor-mity |
| D. | To reduce the reluctance of the mag-netic path |
| Answer» A. To reduce eddy current loss | |
| 48. |
The mechanical power developed by a shunt motor will be maximum when theratio of back e.m.f. to applied voltage is |
| A. | 4.0 |
| B. | 2.0 |
| C. | 1.0 |
| D. | 0.5 |
| Answer» D. 0.5 | |
| 49. |
For which of the following applications a D.C. motor is preferred over an A.C. motor? |
| A. | Low speed operation |
| B. | High speed operation |
| C. | Variable speed operation |
| D. | Fixed speed operation |
| Answer» C. Variable speed operation | |
| 50. |
In D.C. machines the residual magnetism is of the order of |
| A. | 2 to 3 per cent |
| B. | 10 to 15 per cent |
| C. | 20 to 25 per cent |
| D. | 50 to 75 per cent |
| Answer» A. 2 to 3 per cent | |
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