Multiple choice questions (MCQ) on Electrical engineering

Multiple choice questions (MCQ) on Electrical engineering

1. A charge of 240 C is transferred in 2 minutes. The current flowing is:

a. 120 A                b. 480 A            c. 2 A               d. 8 A


2. One kWh of electrical energy equals

a.       3600 J              b. 860 kcal        c. 3600 W         d. 4186 J


3. A 10Ω resistor is connected in parallel with a 15Ω resistor and the combination in series with a 12Ω resistor. The equivalent resistance of the circuit is

a.       37Ω                  b. 18Ω              c. 27Ω              d. 4Ω


4. The total flux in the core of an electrical machine is 20mWb and its flux density is 1T. The cross-sectional area of the core is:

a.       0.05 m2             b. 50 m2            c. 20 m2            d. 0.02 m2


5. The root mean square value of resultant current in a wire carries simultaneously a direct current of 10A, and a sinusoidal alternating current of peak value of 10 A.

a.       14.4                  b. 7.07              c. 11.4              d. 12.2


6. One 200 V, 100 W bulb is connected in series with primary of a 200 V, 10 kVA transformer. If its secondary is left open circuited then the bulb would have

a.       Full brightness                                      b. poor brightness

c.   a little less than full brightness               d. more than full brightness


7. A network with b branches, n nodes, and I independent loops will satisfy which of the following equations

a.       b=l-n+1             b. b=n-l+1         c. b=l+n-1         d. b=l-n-1


8. The losses occurring in a transformer when it is operating at its maximum efficiency are 2000 W. The total copper losses at this load are

a.       2000 W             b. 1000 W         c. 1500 W         d. 800 W


9. A salient pole machine is used for

a.       Low speed applications in Hydro plants             b. High speed applications in Hydro plants

c.    Low speed applications in thermal plants           d. High speed applications in thermal plants


10. If a three phase, 8-pole, 50 Hz induction motor runs at a speed of 735 rpm then the slip is

a.       0.02                  b. 0.03              c. 0.04              d. 0.05


11. What is the form factor of pure sine wave?

a. 1.11              b. 1.414            c. 1.57              d. 0.909


12. In an oil filled transformer, oil is provided for

a. Cooling         b. insulation      c. lubrication                 d. Both cooling and lubrication


13. The numbers of parallel paths in wave wound armature having 4-poles are

a. 2                   b. 4                  c. 6                   d. 8


14. In a Y-Y system, a line voltage of 220V produces a phase voltage of:

a. 381 V            b. 311 V            c. 220 V            d. 127 V


15. When a magnetic flux of 10Wb links with a circuit of 20 turns in 2 s, then the induced emf is

a. 1V                b. 4V                c. 100V             d. 400V


16. The number of PN junctions in a thyristor (SCR) is/are

a. 1                   b. 2                  c. 3                   d. 4


17. A circuit in which the output voltage remains constant irrespective of the value of load resistance uses

a. Silicon diode             b. Zener diode              c. n-p-n transistor          d. p-n-p transistor


18. A fuse is inserted in

a. neutral           b. earth continuity          c. phase           d. both phase and neutral


19. A repulsion motor is equipped with

a. commutator               b. slip rings                   c. a repeller                   d. both (2) & (3)


20. A transformer has negative voltage regulation when its load factor is

a. zero                          b. unity                         c. leading                      d. lagging


21. A 25 MVA, 11Kv alternator is supplying full load at a power factor of 0.75 lagging. Determine the increase in earning capacity when it is operated at improved power factor of 0.96 lagging.

a. 4.56MW        b. 5.90MW        c. 5.25MW        d. 5.02MW


22. Eddy currents always tend

a. To flow in the direction of magnetic flux                  b. To flow in planes perpendicular to magnetic flux

c. Can flow any direction                                          d. None of these


23. Kirchhoff’s law is applicable to

a. Electric circuits                              b. Electronic circuits

c. Junctions in a network                    d. Closed loop in a network


24. The materials having low retentivity are suitable for

a. Temporary magnets               b. Weak magnets          c. Strong magnets         d. Permanent magnets


25. In a p-channel MOSFET the substrate

a. Is p-type       b. Is n-type       c. May be p-type or n-type         d. None of these


26. Constant voltage source is

a. Active and bilateral                b. Passive and bilateral

c. Active and unilateral               d. Passive and unilateral


27. The maximum efficiency of a half wave rectifier circuit can be

a. 37.2%           b. 40.6%           c. 53.9%           d. 81.2%


28. In a D.C. machine the armature m.m.f. is always directed along the

a. Polar axis      b. Brush axis     c. Interpolar axis            d. None of these


29. While drawing phasor diagram for series circuit, the reference phasor is

a. Voltage         b. Current          c. Power           d. Resistance


30. The open circuit test on transformer is performed to obtain

a. Leakage impedances             b. Ohmic losses                        c. Hysteresis losses      d. Core losses


31. In symbols of PNP transistors, and NPN transistors the arrow on the emitter shows the direction of

a. Holes, electrons        b. Electrons, holes        c. Holes, holes              d. Electrons, electrons


32. A commutator in a dc machine can convert

a. a.c. to d.c.                b. d.c. to a.c.                c. Pulsating to d.c.                    d. Both (1) and (2)


33. 1 kWh is equal to

a. 735.5 W        b. 36*105 W       c. 36*105 J        d. 36*107 J


34. The Principle of statically induced emf is utilized in

a. Motor                        b. Generator                  c. Transformer               d. Battery


35. The forbidden energy gap for germanium is

a. 0.3eV            b. 3.5eV            c. 0.7eV           d. 1.12eV


36. If the copper loss of a transformer at 7/8th full load is 4900 W, then its full load copper would be

a. 5600 W         b. 6400 W         c. 373 W           d. 429 W


37. In a transistor, most of the heating occurs at

a. Emitter junction         b. Collector junction                  c. Anywhere                  d. None of these


38. The power factor of an ordinary lamp is

a. Zero              b. Unity             c. Slightly more than unity          d. Slightly less than unity


39. The field on an induction motor rotor rotates with reference to stator at

a. Slip speed                b. Rotor speed        c. Very low speed               d. Synchronous speed


40. The motor used in house hold food mixer is__________motor.

a. shaded pole              b. reluctance               c. universal          d. hysteresis