McqMate
These multiple-choice questions (MCQs) are designed to enhance your knowledge and understanding in the following areas: Mechanical Engineering .
| 1. |
With the increase in the speed of a dc motor: |
| A. | both back emf as well as line current increases |
| B. | both back emf and line current falls |
| C. | back emf increases but the line current falls |
| D. | back emf falls and line current increases |
| Answer» C. back emf increases but the line current falls | |
| 2. |
The output indicated on the name plate of any motor is always the: |
| A. | gross power |
| B. | power drawn in volt amperes |
| C. | power drawn in watts |
| D. | output power at the shaft |
| Answer» D. output power at the shaft | |
| 3. |
The direction of rotation of dc shunt motor can be reversed by interchanging: |
| A. | the supply terminals |
| B. | the field terminals |
| C. | the armature terminals only |
| D. | either field or armature terminals |
| Answer» D. either field or armature terminals | |
| 4. |
The output power of any electrical motor is taken from the: |
| A. | armature |
| B. | field |
| C. | coupling mounted on the shaft |
| D. | motor frame |
| Answer» C. coupling mounted on the shaft | |
| 5. |
If the back emf in a dc motor varnishes suddenly, then the motor: |
| A. | run at very high speeds |
| B. | start hunting |
| C. | burn |
| D. | come to stall |
| Answer» C. burn | |
| 6. |
The direction of the armature current in a dc motor is: |
| A. | the same as the generated emf |
| B. | opposite to that of generated emf |
| C. | not dependent upon the direction of the armature emf |
| D. | none of the above |
| Answer» B. opposite to that of generated emf | |
| 7. |
When a dc machine is connected to the dc supply main it will produce: |
| A. | emf in opposition to the applied voltage |
| B. | emf in phase with the applied voltage |
| C. | emf decreases with time |
| D. | none of the above |
| Answer» A. emf in opposition to the applied voltage | |
| 8. |
The direction of rotation of a dc motor can be determined by: |
| A. | fleming\s right hand rule |
| B. | fleming\s left hand rule |
| C. | lenz\s law |
| D. | ampere\s law |
| Answer» B. fleming\s left hand rule | |
| 9. |
A thick wire is used in dc series motor field winding than that in dc shunt motor: |
| A. | to create more flux |
| B. | to reduce the resistance |
| C. | to carry large load current |
| D. | both (b) and © |
| Answer» D. both (b) and © | |
| 10. |
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: |
| A. | drop in the speed and rise in the current |
| B. | rise in the speed and drop in the current |
| C. | rise in the speed and rise in the current |
| D. | drop in speed with current unaltered |
| Answer» A. drop in the speed and rise in the current | |
| 11. |
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: |
| A. | remains unchanged |
| B. | increases |
| C. | decreases |
| D. | be zero |
| Answer» C. decreases | |
| 12. |
A DC series motor is best suited for electrical traction because: |
| A. | it develops high starting torque |
| B. | it runs at very high speed |
| C. | it is cheaper in cost |
| D. | it is more rugged in construction like induction motor |
| Answer» A. it develops high starting torque | |
| 13. |
Which of the following dc motor has maximum self relieving property: |
| A. | shunt |
| B. | series |
| C. | cumulative compound |
| D. | differential compound |
| Answer» B. series | |
| 14. |
When the direction of power flow in a differential compounded motor reverses, it will operate as a: |
| A. | cumulative compound generator |
| B. | differential compound generator |
| C. | series motor |
| D. | shunt motor |
| Answer» A. cumulative compound generator | |
| 15. |
A flywheel is employed with a dc compound motor to reduce the peak demand, the compound motor should be: |
| A. | level compound |
| B. | differential compound |
| C. | cumulative compound |
| D. | none of the above |
| Answer» C. cumulative compound | |
| 16. |
The output voltage of a DC generator is |
| A. | e = v + iara |
| B. | e = v – iara |
| C. | e = v + ia |
| D. | e = v + ra |
| Answer» A. e = v + iara | |
| 17. |
The material used for commutator brushes is mostly |
| A. | copper |
| B. | carbon |
| C. | mica |
| D. | cast iron |
| Answer» B. carbon | |
| 18. |
A 4 pole DC generator rotates at 1500 rpm. How many times in a second, will the emf induced in each armature conductor changes its direction? |
| A. | 750 |
| B. | 100 |
| C. | 500 |
| D. | 200 |
| Answer» B. 100 | |
| 19. |
Magnetic field of a DC generator is produced by what? |
| A. | permanent magnets |
| B. | electromagnets |
| C. | both option b & c |
| D. | none of the options |
| Answer» B. electromagnets | |
| 20. |
In a DC generator the emf generated by the armature is maximum when |
| A. | rate of change of flux is maximum |
| B. | rate of change of flux is minimum |
| C. | induced voltage is high |
| D. | shaft rotation is high |
| Answer» A. rate of change of flux is maximum | |
| 21. |
What is the actual arrangement of series wound generator? |
| A. | armature and field both are parallel |
| B. | armature and field both are connected |
| C. | increase the speed of shaft rotation |
| D. | armature and field both are in series with the load |
| Answer» D. armature and field both are in series with the load | |
| 22. |
What is the effect of armature reaction? |
| A. | armature flux weakens the main field flux |
| B. | armature flux distorts the main field flux |
| C. | both option b & a |
| D. | none of the options |
| Answer» C. both option b & a | |
| 23. |
In DC machine, brushes are always placed along |
| A. | magnetic neutral axis |
| B. | geometrical neutral axis |
| C. | armature axis |
| D. | load axis |
| Answer» A. magnetic neutral axis | |
| 24. |
What type of connection is made in between the interpole & the field winding? |
| A. | series |
| B. | parallel |
| C. | compound |
| D. | none of the options |
| Answer» B. parallel | |
| 25. |
In DC machine, lap winding is used in |
| A. | high current and low voltage applications |
| B. | high voltage and low current applications |
| C. | where constant speed is required |
| D. | where greater load is connected |
| Answer» A. high current and low voltage applications | |
| 26. |
The basic requirement of a dc armature winding is that it must be |
| A. | a closed one |
| B. | a lap winding |
| C. | a wave winding |
| D. | either b or c |
| Answer» A. a closed one | |
| 27. |
The sole purpose of a commutator in a dc generator is to |
| A. | increase output voltage |
| B. | reduce sparking at brushes |
| C. | provide smoother output |
| D. | convert the induced ac into dc |
| Answer» D. convert the induced ac into dc | |
| 28. |
In a dc generator, the generator, the generated emf is directly proportional to the |
| A. | field current |
| B. | pole flux |
| C. | number of armature parallel paths |
| D. | number of dummy coils |
| Answer» B. pole flux | |
| 29. |
Voltage equation of a dc motor is |
| A. | v = eb + iara |
| B. | eb = v + iara |
| C. | v = eb/iara |
| D. | v = eb + ia2ra |
| Answer» A. v = eb + iara | |
| 30. |
which of the following motor has the constant speed? |
| A. | series motor |
| B. | shunt motor |
| C. | cumulatively compound motor |
| D. | all of the above |
| Answer» B. shunt motor | |
| 31. |
The usual test to find the efficiency of the traction motor is |
| A. | field\s test |
| B. | retardation test |
| C. | hopkinson\s test |
| D. | swinburn\s test |
| Answer» A. field\s test | |
| 32. |
A DC series motor is best for driving |
| A. | lathes |
| B. | cranes and hoists |
| C. | shears and punches |
| D. | machine tools |
| Answer» B. cranes and hoists | |
| 33. |
In a DC series motor increasing the load current will |
| A. | decrease the speed |
| B. | increase the speed |
| C. | better commutation |
| D. | increase the back emf |
| Answer» A. decrease the speed | |
| 34. |
The DC motor, which can provide zero speed regulation at full load without any controller is |
| A. | series |
| B. | shunt |
| C. | cumulative compound |
| D. | differential compound |
| Answer» B. shunt | |
| 35. |
In 8 - pole wave connected motor armature, the number of parallel paths are |
| A. | 8 |
| B. | 4 |
| C. | 2 |
| D. | 1 |
| Answer» C. 2 | |
| 36. |
The speed of a dc motor can be controlled by varying |
| A. | its flux per pole |
| B. | resistance of armature circuit |
| C. | applied voltage |
| D. | all of the above |
| Answer» D. all of the above | |
| 37. |
The d.c. series motor should always be started with load because |
| A. | at no load, it will rotate at dangerously high speed. |
| B. | it will fail to start. |
| C. | it will not develop high starting torque. |
| D. | all are true. |
| Answer» A. at no load, it will rotate at dangerously high speed. | |
| 38. |
In a d.c. machine, the armature mmf is |
| A. | stationary w.r.t. armature. |
| B. | rotating w.r.t. field. |
| C. | stationary w.r.t. field. |
| D. | rotating w.r.t. brushes. |
| Answer» C. stationary w.r.t. field. | |
| 39. |
In a DC motor, unidirectional torque is produced with the help of |
| A. | brushes |
| B. | commutator |
| C. | end-plates |
| D. | both a and b |
| Answer» D. both a and b | |
| 40. |
The counter emf of dc motor |
| A. | often exceeds the supply voltage |
| B. | aids the applied voltage |
| C. | helps in energy conversion |
| D. | regulates its armature voltage |
| Answer» C. helps in energy conversion | |
| 41. |
The Eb/V ratio of a dc motor is an indication of its |
| A. | efficiency |
| B. | speed regulation |
| C. | starting torque |
| D. | running torque |
| Answer» A. efficiency | |
| 42. |
The induced emf in the armature conductors of a dc motor is |
| A. | sinusoidal |
| B. | trapezoidal |
| C. | rectangular |
| D. | alternating |
| Answer» A. sinusoidal | |
| 43. |
A dc motor can be looked upon as dc generator with the power flow |
| A. | reduced |
| B. | reversed |
| C. | increased |
| D. | modified |
| Answer» B. reversed | |
| 44. |
The Ta/Ia graph of a dc series motor is a |
| A. | parabola from no load to overload |
| B. | straight line throughout |
| C. | parabola throughout |
| D. | parabola upto full load and a straight line at overloads |
| Answer» D. parabola upto full load and a straight line at overloads | |
| 45. |
When load is removed, .......motor will run at the highest speed. |
| A. | shunt |
| B. | cumulative - compound |
| C. | differential compound |
| D. | series |
| Answer» D. series | |
| 46. |
In Fleming's right-hand rule, the thumb point towards |
| A. | direction of flux |
| B. | direction of induced e.m.f. |
| C. | direction of motion of conductor, if fore finger points along the lines of flux |
| D. | direction of motion of the conductor\ if fore finger point in the direction of generated e.m.f. |
| Answer» C. direction of motion of conductor, if fore finger points along the lines of flux | |
| 47. |
. The armature of a dc machine is made of____. |
| A. | silicon steel |
| B. | wrought iron |
| C. | cast steel |
| D. | soft iron |
| Answer» A. silicon steel | |
| 48. |
The yoke of a d.c. machine is made of ____. |
| A. | silicon steel |
| B. | soft iron |
| C. | aluminum |
| D. | cast steel |
| Answer» D. cast steel | |
| 49. |
. The coupling field electrical and mechanical systems of dc machine is____. |
| A. | electric field |
| B. | magnetic field |
| C. | both electric and magnetic fields |
| D. | mechanical field |
| Answer» B. magnetic field | |
| 50. |
The real working part of a dc machine is the ___. |
| A. | commutator |
| B. | field winding |
| C. | armature winding |
| D. | none of the above |
| Answer» C. armature winding | |
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