MCQOPTIONS
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MCQOPTIONS
This section includes 57 Mcqs, each offering curated multiple-choice questions to sharpen your Electrical Engineering knowledge and support exam preparation. Choose a topic below to get started.
| 1. |
The degree of mechanical vibrations produced by the laminations of a transformer depends on |
| A. | tightness of clamping |
| B. | gauge of laminations |
| C. | size of laminations |
| D. | all of the above |
| Answer» E. | |
| 2. |
The no-load current drawn by transformer is usually what per cent of the full-load current ? |
| A. | 0.2 to 0.5 per cent |
| B. | 2 to 5 per cent |
| C. | 12 to 15 per cent |
| D. | 20 to 30 per cent |
| Answer» C. 12 to 15 per cent | |
| 3. |
Auto-transformer makes effective saving on copper and copper losses, whenits transformation ratio is |
| A. | approximately equal to one |
| B. | less than one |
| C. | great than one |
| D. | none of the above |
| Answer» B. less than one | |
| 4. |
In a step-down transformer, there is a change of 15 A in the load current. This results in change of supply current of |
| A. | less than 15 A |
| B. | more than 15 A |
| C. | 15 A |
| D. | none of the above |
| Answer» B. more than 15 A | |
| 5. |
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» B. rheostatic control | |
| 6. |
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» E. | |
| 7. |
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» D. Stator | |
| 8. |
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» E. | |
| 9. |
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» E. | |
| 10. |
Which of the following load normally needs starting torque more than therated torque? |
| A. | Blowers |
| B. | Conveyors |
| C. | Air compressors |
| D. | Centrifugal pumps |
| Answer» C. Air compressors | |
| 11. |
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» D. 10% of the previous value | |
| 12. |
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» D. Differentially compounded motor | |
| 13. |
Reduction in core losses and increase in permeability are obtained with transformer employing |
| A. | core built-up of laminations of cold rolled grain oriented steel |
| B. | core built-up of laminations of hot rolled sheet |
| C. | either of the above |
| D. | none of the above |
| Answer» B. core built-up of laminations of hot rolled sheet | |
| 14. |
Which of the following statements regarding an idel single-phase transformerhaving a turn ratio of 1 : 2 and drawing a current of 10 A from 200 V A.C. supply is incorrect ? |
| A. | Its secondary current is 5 A |
| B. | Its secondary voltage is 400 V |
| C. | Its rating is 2 kVA |
| D. | Its secondary current is 20 A |
| Answer» E. | |
| 15. |
In a given transformer for a given applied voltage, losses which remainconstant irrespective of load changes are |
| A. | hysteresis and eddy current losses |
| B. | friction and windage losses |
| C. | copper losses |
| D. | none of the above |
| Answer» B. friction and windage losses | |
| 16. |
Which of the following is the main advantage of an auto-transformer over a two winding transformer ? |
| A. | Hysteresis losses are reduced |
| B. | Saving in winding material |
| C. | Copper losses are negligible |
| D. | Eddy losses are totally eliminated |
| Answer» C. Copper losses are negligible | |
| 17. |
The secondary of a current transformer is always short-circuited underoperating conditions because it |
| A. | avoids core saturation and high voltage induction |
| B. | is safe to human beings |
| C. | protects the primary circuit |
| D. | none of the above |
| Answer» B. is safe to human beings | |
| 18. |
Which of the following acts as a protection against high voltage surges due to lightning and switching ? |
| A. | Horn gaps |
| B. | Thermal overload relays |
| C. | Breather |
| D. | Conservator |
| Answer» B. Thermal overload relays | |
| 19. |
Which of the following protection is normally not provided on smalldistribution transformers ? |
| A. | Overfluxing protection |
| B. | Buchholz relay |
| C. | Overcurrent protection |
| D. | All of the above |
| Answer» C. Overcurrent protection | |
| 20. |
The efficiency of two identical transformers under load conditionscan be determined by |
| A. | short-circuit test |
| B. | back-to-back test |
| C. | open circuit test |
| D. | any of the above |
| Answer» C. open circuit test | |
| 21. |
Which of the following insulating materials can withstand the highest temperature safely ? |
| A. | Cellulose |
| B. | Asbestos |
| C. | Mica |
| D. | Glass fibre |
| Answer» D. Glass fibre | |
| 22. |
The changes in volume of transformer cooling oil due to variation of atmospheric temperature during day and night is taken care of by which part of transformer |
| A. | Conservator |
| B. | Breather |
| C. | Bushings |
| D. | Buchholz relay |
| Answer» B. Breather | |
| 23. |
For the parallel operation of single phase transformers it is necessary that they should have |
| A. | same efficiency |
| B. | same polarity |
| C. | same kVA rating |
| D. | same number of turns on the secondary side. |
| Answer» C. same kVA rating | |
| 24. |
Which of the following property is not necessarily desirable in the material for transformer core ? |
| A. | Mechanical strength |
| B. | Low hysteresis loss |
| C. | High thermal conductivity |
| D. | High permeability |
| Answer» D. High permeability | |
| 25. |
Gas is usually not liberated due to dissociation of transformer oil unless the oil temperature exceeds |
| A. | 50 C |
| B. | 80 C |
| C. | 100 C |
| D. | 150 C |
| Answer» E. | |
| 26. |
Which of the following properties is not necessarily desirable for the material for transformer core ? |
| A. | Low hysteresis loss |
| B. | High permeability |
| C. | High thermal conductivity |
| D. | Adequate mechanicalstrength |
| Answer» D. Adequate mechanicalstrength | |
| 27. |
Which of the following tests will be suitable for testing two similar D.C. series motors of large capacity ? |
| A. | Swinburne'stest |
| B. | Hopkinson'stest |
| C. | Field test |
| D. | Brake test |
| Answer» D. Brake test | |
| 28. |
A 220 V D.C. generator is run at full speed without any excitation. The open circuit voltage will be |
| A. | zero |
| B. | about 2 V |
| C. | about 50 V |
| D. | 220V |
| Answer» C. about 50 V | |
| 29. |
The terminal voltage of a D.C. shunt generator drops on load because of all of the following reasons except |
| A. | armature reaction |
| B. | armature resistance drop |
| C. | field weakening due to armature reaction and armature |
| D. | commut ation |
| Answer» E. | |
| 30. |
Which of the following motors is most suitable for signalling devices and many kinds of timers ? |
| A. | D.C. shunt motor |
| B. | D.C. series motor |
| C. | Induction motor |
| D. | Reluctance motor |
| Answer» E. | |
| 31. |
D.C. generators are connected to the busbars or disconnected from them only under the floating condition |
| A. | to avoid sudden loading of the primemover |
| B. | to avoid mechanicaljerk to the shaft |
| C. | to avoid burning of switch contacts |
| D. | all above |
| Answer» E. | |
| 32. |
In any rotating machine that part which houses the conductors and in which e.m.f. induced is to be utilised is called |
| A. | rotor |
| B. | stator |
| C. | field |
| D. | armature |
| Answer» E. | |
| 33. |
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» D. All of the above | |
| 34. |
If B is the flux density, I the length of conductor and v the velocity of conductor, then induced e.m.f. is given by |
| A. | Blv |
| B. | Blv2 |
| C. | Bl2v |
| D. | Bl2v2 |
| Answer» B. Blv2 | |
| 35. |
Which of the following components of a D.C, generator plays vital role for providing direct current of a D.C. generator ? |
| A. | Dummy coils |
| B. | Commutator |
| C. | Eye bolt |
| D. | Equilizer rings |
| Answer» C. Eye bolt | |
| 36. |
The voltage drop for which of the following types of brush can be expected to be least? |
| A. | Graphite brushes |
| B. | Carbon brushes |
| C. | Metal graphite brushes |
| D. | None of the above |
| Answer» D. None of the above | |
| 37. |
In a D.C. generator the number of mechanical degrees and electrical degrees will be the same when |
| A. | r.p.m. is more than 300 |
| B. | r.p.m. is less than 300 |
| C. | number of poles is 4 |
| D. | number of poles is 2 |
| Answer» E. | |
| 38. |
Which of the following could be lamina-proximately the thickness of laminations of a D.C. machine ? |
| A. | 0.005 mm |
| B. | 0.05 mm |
| C. | 0.5 m |
| D. | 5 m |
| Answer» D. 5 m | |
| 39. |
To achieve sparkless commutation brushes of a D.C. generator are rockedm ahead soas to bring them |
| A. | just ahead of magnetic neutral axis |
| B. | in magnetic neutral axis |
| C. | just behind the magnetic neutral axis |
| D. | none |
| Answer» B. in magnetic neutral axis | |
| 40. |
Which of the following generating machine will offer constant voltage on all loads ? |
| A. | Self-excited generator |
| B. | Separately excited generator |
| C. | Level compounded generator . |
| D. | All of the above |
| Answer» D. All of the above | |
| 41. |
Two generators are running in parallel. One of the generators may run as motor for which of the following reasons ? |
| A. | The direction of that generator is reversed |
| B. | The speed of that generator is increased |
| C. | The field of that generator is weakened |
| D. | That generator takes large share of loads |
| Answer» E. | |
| 42. |
Which of the following method of speed control of D.C. machine will offer minimum efficiency ? |
| A. | Voltage control method |
| B. | Field control method |
| C. | Armature control method |
| D. | All above methods |
| Answer» D. All above methods | |
| 43. |
Which of the following generators will be preferred if they are required to be run in parallel ? |
| A. | Shunt generators |
| B. | Series generators |
| C. | Compound generators |
| D. | None of the above |
| Answer» B. Series generators | |
| 44. |
The essential condition for parallel operation of two D.C. generators is that they have ' |
| A. | same kW rating |
| B. | the same operation r.p.m. |
| C. | the same drooping voltage charac-teristics |
| D. | same percentage regulation |
| Answer» D. same percentage regulation | |
| 45. |
For both lap and wave windings, there are as many commutator bars as the numberof |
| A. | slots |
| B. | armature conductors |
| C. | winding elements |
| D. | poles |
| Answer» D. poles | |
| 46. |
Buses, trains, trolleys, hoists, cranes require high starting torque and therefore make use of |
| A. | D.C. series motor |
| B. | D.C. shunt motor |
| C. | induction motor |
| D. | all of above motors |
| Answer» B. D.C. shunt motor | |
| 47. |
As there is no back e.m.f. at the instant of starting a D.C. motor, in order to prevent a heavy current from flowing though the armature circuit |
| A. | a resistance is connected in series with armature |
| B. | a resistance is connected parallel to the armature |
| C. | armature is temporarily open circuited |
| D. | a high value resistor is connected across the fieldwinding |
| Answer» B. a resistance is connected parallel to the armature | |
| 48. |
As a result of armature reaction, the reduction in the total mutual air gap flux in aD.C. generator is approximately |
| A. | 40 percent |
| B. | 25 percent |
| C. | 10 percent |
| D. | 5 percent |
| Answer» E. | |
| 49. |
The number of armature parallel paths in a two-pole D.C. generator having duplexlap winding is |
| A. | 2 |
| B. | 4 |
| C. | 6 |
| D. | 8 |
| Answer» C. 6 | |
| 50. |
Following D.C. generator will be in a position to build up without any residual magnetism in the poles |
| A. | series generator |
| B. | shunt generator |
| C. | compound generator |
| D. | self-excited generator |
| Answer» E. | |