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MCQOPTIONS
This section includes 378 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. |
A DC shunt generator supplies a load of 7.5 kW at 200 V. If the armature resistance is 0.6 Ω and field resistance is 80 Ω, the induced emf will be |
| A. | 224 V |
| B. | 218 V |
| C. | 212 V |
| D. | 204 V |
| Answer» B. 218 V | |
| 2. |
A DC generator delivers a 30-A current to a load at 120 V by consuming 4500 J/s of mechanical energy. Determine the efficiency of the generator. |
| A. | 90% |
| B. | 85% |
| C. | 75% |
| D. | 80% |
| Answer» E. | |
| 3. |
Field coils of DC generator are usually made up of |
| A. | mica |
| B. | copper |
| C. | cast iron |
| D. | carbon |
| Answer» C. cast iron | |
| 4. |
In lap winding, the number of parallel paths are always: |
| A. | Same as the number of poles |
| B. | Half the number of poles |
| C. | Double the number of poles |
| D. | Two |
| Answer» B. Half the number of poles | |
| 5. |
In DC machines, the distance between two adjacent poles can be defined as: |
| A. | pole size |
| B. | armature length |
| C. | pole-pitch |
| D. | coil length |
| Answer» D. coil length | |
| 6. |
In dc machines, the field – flux axis and armature – mmf axis are respectively placed along |
| A. | direct axis and indirect axis |
| B. | direct axis and interpolar axis |
| C. | quadrature axis and direct axis |
| D. | quadrature axis and interpolar axis |
| Answer» C. quadrature axis and direct axis | |
| 7. |
In a 6-pole DC machine, with lap winding, the number of parallel paths in the armature will be: |
| A. | 3 |
| B. | 6 |
| C. | 4 |
| D. | 2 |
| Answer» C. 4 | |
| 8. |
A series motor of resistance 1 Ω between terminals runs at 800 rpm at 200 V with a current of 15 A. Determine the speed at which it will run when connected in series with a 5 Ω resistance and taking the same current at the same supply voltage |
| A. | 1254 rpm |
| B. | 476 rpm |
| C. | 1079.6 rpm |
| D. | 409.3 rpm |
| Answer» C. 1079.6 rpm | |
| 9. |
Match List-I (types of DC Generators with List-II (Applications) and select the correct answer using the given options.List-IList-IIA. Series Generator1. Arc weldingB. Shunt Generator2. Supply of distant loadsC. Cumulative Compounded3. BoosterD. Differentially Compounded4. battery Charging |
| A. | A-1, B-4, C-3, D-2 |
| B. | A-3, B-4, C-2, D-1 |
| C. | A-3, B-4, C-1, D-2 |
| D. | A-4, B-3, C-2, D-1 |
| Answer» C. A-3, B-4, C-1, D-2 | |
| 10. |
Determine the generated EMF of the given generator if the armature resistance is 0.1 Ω. |
| A. | 225.75 V |
| B. | 230.00 V |
| C. | 185.50 V |
| D. | 275.46 V |
| Answer» E. | |
| 11. |
In an electric machine F2 (rotor mmf) = 920 AT. F1 (stator emf) = 400 AT, alpha = 125° and the resultant air gap flux per pole is 0.107 Wb. Find out permeance per pole.Note: AT (Ampere Turn) is a unit. |
| A. | 1.408 × 10-4 Wb/AT |
| B. | 8.408 × 10-4 Wb/AT |
| C. | 2.480 × 10-4 Wb/AT |
| D. | 2.408 × 10-4 Wb/AT |
| Answer» B. 8.408 × 10-4 Wb/AT | |
| 12. |
A dc generator delivers 30 A at 120 V and it is driven by mechanical energy at the rate of 4000 J/s determine the percentage efficiency of the generator. |
| A. | 92% |
| B. | 88% |
| C. | 90% |
| D. | 86% |
| Answer» D. 86% | |
| 13. |
A separately excited DC generator has a no-load voltage of 127 V, Ra = 0.02 Ω and Rsh = 15Ω Find the armature current when the generator terminal voltage is 120 V on load. |
| A. | 350 A |
| B. | 150 A |
| C. | 220 A |
| D. | 10 A |
| Answer» B. 150 A | |
| 14. |
Dummy coil in a d.c. generator is provided to reduce ________ |
| A. | mechanical unbalance |
| B. | hysteresis losses |
| C. | armature reaction |
| D. | tendency of reversal |
| Answer» B. hysteresis losses | |
| 15. |
Equalizer bus is necessary for the parallel operation of the: |
| A. | Series generator only |
| B. | series and over compound generators |
| C. | series and under compound generators |
| D. | Over compounded generator only |
| Answer» C. series and under compound generators | |
| 16. |
A 4 pole generator with 16 coils has two layer lap winding. The pole pitch is ________. |
| A. | 8 |
| B. | 32 |
| C. | 16 |
| D. | 4 |
| Answer» B. 32 | |
| 17. |
If the total number of slots in a D.C machine is 25 and the total number of poles is 5, then what is the coil span of the machine? |
| A. | 5 |
| B. | 30 |
| C. | 20 |
| D. | 125 |
| Answer» B. 30 | |
| 18. |
A wave winding must go at least ______ around the armature before it closes back where it started. |
| A. | four times |
| B. | thrice |
| C. | twice |
| D. | once |
| Answer» D. once | |
| 19. |
How can a load be shifted from one DC shunt generator to another running in parallel? |
| A. | Adjust their field rheostat |
| B. | Insert a resistance in the armature circuit |
| C. | Adjust the speed of the prime mover |
| D. | Use an equaliser connection |
| Answer» B. Insert a resistance in the armature circuit | |
| 20. |
In a 4 pole, 25 kW, 200 V wave wound DC shunt generator, the current in each parallel path will be _______. |
| A. | 62.5 A |
| B. | 125 A |
| C. | 31.25 A |
| D. | 250 A |
| Answer» B. 125 A | |
| 21. |
In a DC machine, let ϕ be the flux per pole, ωm be the armature speed in rad / s, Nc be the number of coil turns in the armature and P be the number of poles. What will be the average coil EMF in that machine? |
| A. | \({E_a} = \dfrac{{\phi {\omega _m}{N_c}}}{P}\) |
| B. | \({E_a} = \dfrac{{\phi {\omega _m}{N_c}P}}{{60}}\) |
| C. | Ea = ϕωmNcP |
| D. | \({E_a} = \dfrac{{\phi {\omega _m}{N_c}P}}{\pi }\) |
| Answer» E. | |
| 22. |
Force on a Conductors is |
| A. | Unidirectional |
| B. | Bidirectional |
| C. | Either of these |
| D. | None of these |
| Answer» B. Bidirectional | |
| 23. |
In case if a dc machine, the value of load current at maximum efficiency is: |
| A. | IL = √(constant losses / armature resistance) |
| B. | IL = √(variable losses / armature resistance) |
| C. | IL = √(variable loss + constant losses / armature resistance) |
| D. | IL = √(constant losses / Ra + Rf) |
| Answer» B. IL = √(variable losses / armature resistance) | |
| 24. |
If we observe the output waveform of DC generator on CRO, it will be like a _____. |
| A. | sinusoidal wave |
| B. | square wave |
| C. | constant voltage line |
| D. | pulsating unidirectional waveform |
| Answer» D. pulsating unidirectional waveform | |
| 25. |
In DC generators, wave windings are preferred for |
| A. | high current, low voltage |
| B. | high current, high voltage |
| C. | low current, high voltage |
| D. | low current, low voltage |
| Answer» D. low current, low voltage | |
| 26. |
In a 4 pole, 20 kW, 200 V wave wound DC shunt generator, the current in each parallel path will be _______. |
| A. | 100 A |
| B. | 25 A |
| C. | 10 A |
| D. | 50 A |
| Answer» E. | |
| 27. |
A dc generator is operating at constant speed and constant field excitation. If it is supplying maximum power at a voltage of 220 V then the generated emf |
| A. | Is 110 V |
| B. | Is 220 V |
| C. | Is 440 V |
| D. | Depends upon the armature resistance |
| Answer» D. Depends upon the armature resistance | |
| 28. |
__________ type of DC generator does not need equalisers for satisfactory parallel operation. |
| A. | Over-compound |
| B. | Series |
| C. | Flat-compound |
| D. | Under-compound |
| Answer» E. | |
| 29. |
A 250 V DC generator is run at rated speed with no excitation. The open circuit voltage will be: |
| A. | Zero |
| B. | Very small, say about 2 or 3 V |
| C. | About 100 V |
| D. | 250 V |
| Answer» C. About 100 V | |
| 30. |
A DC shunt motor is running at 1000 rpm when supplied from a 240 V DC. Neglecting losses and magnetic saturation, the speed of the motor when connected to 180 V DC source will be |
| A. | 1000 rpm |
| B. | 750 rpm |
| C. | 1350 rpm |
| D. | 1200 rpm |
| Answer» B. 750 rpm | |
| 31. |
For a Lap wound generator, the number of parallel paths in armature is taken to be: |
| A. | 4 |
| B. | 2 |
| C. | number of poles / 2 |
| D. | number of poles |
| Answer» E. | |
| 32. |
For a d.c. shunt generator to self excite, the conditions to be satisfied are that there must be some residual magnetism in the field magnet, it must be in the proper direction and the shunt field resistant must be |
| A. | Above the critical field resistance |
| B. | Equal to the critical field resistance |
| C. | Less than the armature resistance |
| D. | Less than the critical field resistance |
| Answer» E. | |
| 33. |
In a d.c. series motor, the torque developed is 20 Nm at 10 A. If the load current is doubled and flux is unsaturated, then new torque will be: |
| A. | 60 Nm |
| B. | 45 Nm |
| C. | 80 Nm |
| D. | 100 Nm |
| Answer» D. 100 Nm | |
| 34. |
A shunt generator has an induced e.m.f. of 224 V. When supplying a load, the terminal voltage falls to 204 V. The armature and shunt field resistances are 0.05 Ω and 20 Ω, respectively. The load current, neglecting the armature reaction, is |
| A. | 376.0 A |
| B. | 389.8 A |
| C. | 400.0 A |
| D. | 410.2 A |
| Answer» C. 400.0 A | |
| 35. |
A 120 V DC shunt motor takes 2 A at no laod. It takes 7 A on full load while running at 1200 rpm. Given Ra = 0.8 Ω and Rsh = 240 Ω, find no load speed in rpm. |
| A. | 4212.28 rpm |
| B. | 1282.82 rpm |
| C. | 1824.82 rpm |
| D. | 1241.82 rpm |
| Answer» E. | |
| 36. |
In a dc generator, the process of reversal of current in an armature coil as it crosses magnetic neutral axis is called: |
| A. | commutation |
| B. | demagnetisation |
| C. | armature reaction |
| D. | cross magnetisation |
| Answer» B. demagnetisation | |
| 37. |
A DC generator efficiency is maximum when: |
| A. | Constant loss - variable loss = 1 |
| B. | Variable loss - Constant loss = 1 |
| C. | Variable loss - Constant loss = 0 |
| D. | Variable loss + Constant loss = 1 |
| Answer» D. Variable loss + Constant loss = 1 | |
| 38. |
In armature winding. the distance between the segments to which the ends of coils are connected is? |
| A. | resultant pitch |
| B. | front pitch |
| C. | commutator pitch |
| D. | back pitch |
| Answer» D. back pitch | |
| 39. |
A 4-ploe generator has a wave-wound armature with 750 conductors, and it delivers 100 A on full load. Calculate the armature demagnetizing and cross-magnetizing A-T/pole, if the brush lead is 8°. |
| A. | Demagnetizing A-T/pole = 800; cross-magnetizing A – T/pole = 3700 |
| B. | Demagnetizing A-T/pole = 3700; cross-magnetizing A-T/pole = 800 |
| C. | Demagnetizing a-T/pole = 80; cross-magnetizing A-T/pole = 370 |
| D. | Demagnetizing A –T/pole = 370; cross-magnetizing A-T/pole = 800 |
| Answer» B. Demagnetizing A-T/pole = 3700; cross-magnetizing A-T/pole = 800 | |
| 40. |
In a DC generator, when the magnetic neutral axis coincides with the geometrical neutral axis? |
| A. | There is no load on the generator |
| B. | The generator runs at full load |
| C. | The generator runs on over load |
| D. | The generator runs on designed speed |
| Answer» B. The generator runs at full load | |
| 41. |
If the field circuit resistance of a d.c. generator exceed its critical value, then the generator: |
| A. | Fails to build up |
| B. | Builds up a very high voltage |
| C. | Exceeds its current capacity |
| D. | Produces power beyond its rating |
| Answer» B. Builds up a very high voltage | |
| 42. |
In a DC generator, let P be the number of poles, Φ be the flux per pole, Z be the number of armature conductors and A be the number of parallel paths in armature. If the generator runs at N rpm, then the generated emf per parallel path is: |
| A. | \( \frac{{ZP\phi N}}{{\pi A}}\) V |
| B. | \( \frac{{ZP\phi N}}{{120\;A}}\) V |
| C. | \( \frac{{2\pi ZP\phi N}}{{60\;A}}\)V |
| D. | \(\frac{{ZP\phi N}}{{60\;A}}\) V |
| Answer» E. | |
| 43. |
A DC shunt motor running on full load takes 50 A. If the supply voltage and field current is reduced to half, what will be the armature current if motor delivers constant power output ? (Assume armature resistance is negligible) |
| A. | 100 A |
| B. | 200 A |
| C. | 50 A |
| D. | 25 A |
| Answer» B. 200 A | |
| 44. |
A separately excited DC motor has an armature resistance of 0.5 Ω. It runs from a 250 V DC supply drawing an armature current of 20 A at 1500 rpm. The torque developed for an armature current of 10 A for the same field current will be: |
| A. | 15.28 Nm |
| B. | 15.92 Nm |
| C. | 15.6 Nm |
| D. | 16.55 Nm |
| Answer» B. 15.92 Nm | |
| 45. |
A DC series motor takes 40 A at 220 V and runs at 800 rpm. If the armature and field resistance are 0.2 Ω and 0.1 Ω respectively, find the torque developed in the armature. |
| A. | 99.3 Nm |
| B. | 9.93 Nm |
| C. | 93 Nm |
| D. | 89 Nm |
| Answer» B. 9.93 Nm | |
| 46. |
If a DC compound machine connected as a generator is run as a motor, the series field connections must be in _______, as the armature current ______. |
| A. | reverse direction; remains same |
| B. | reverse direction; reverses |
| C. | forward direction; reverses |
| D. | forward direction; remains same |
| Answer» C. forward direction; reverses | |
| 47. |
In DC generator, pole shoes are fastened to pole core by: |
| A. | Rivets |
| B. | Brazing |
| C. | Welding |
| D. | Countersunk screws |
| Answer» E. | |
| 48. |
Mechanical efficiency of a diesel engine is defined as ________. |
| A. | BHP ÷ IHP |
| B. | BHP × IHP |
| C. | IHP – BHP |
| D. | IHP ÷ BHP |
| Answer» B. BHP × IHP | |
| 49. |
DC motors are still preferred for use in: |
| A. | Electric excavators, steel mills and cranes |
| B. | Lathes and machine tools |
| C. | Flour mills and jaw crushers |
| D. | Paper industry |
| Answer» B. Lathes and machine tools | |
| 50. |
In a 6-pole DC machine, 90 mechanical degrees corresponds to how many electrical degrees? |
| A. | 270 |
| B. | 180 |
| C. | 30 |
| D. | 45 |
| Answer» B. 180 | |