Important MCQ of Electrical Engineering


1. Two infinite parallel conductors carry parallel currents 10A each. Find the magnitude and
direction of the force between the conductors per meter length if the distance between them is
20cm.
a. 10-3N
b. 10-4N
c. 103N
d. 104N
2. Calculate the magnetising force and flux density at a distance of 5cm from a long straight
circular conductor carrying a current of 250A and placed in air.
a. 795.6 AT/m, 10-3 Wb/m2
b. 79.56 AT/m, 10-3 Wb/m2
c. 795.6 AT/m, 10-2 Wb/m2
d. 795.6 AT/m, 10-3 Wb/m
3. A wire 5m long is bent into a circle. If the current flowing through the wire is 200 A, find the
magnetising force at the centre of the circle.
a. 125.6 AT/m
b. 105.6 AT/m
c. 125.6 AT/m2
d. 105.6 AT/m2
4. Which of the following magnetic materials can be easily magnetized in both directions?
a. Soft magnetic materials
b. Hard magnetic materials
c. High hysteresis loss materials
d. Low hysteresis loss materials
5. A sine wave of 15 kHz is changing at a faster rate than a sine wave with a frequency of
a. 12 kHz
b. 18 kHz
c. 25 kHz
d. 1.3 MHz
6. A sinusoidal current has an rms value of 14 mA. The peak-to-peak value is
a. 45.12 mA
b. 39.6 mA
c. 16 mA
d. 22.6 mA
7. Sine wave A has a positive-going zero crossing at 45°. Sine wave B has a positive-going zero
crossing at 60°. Which of the following statements is true?
a. Wave A leads wave B by 15°
b. Wave A lags wave B by 105°.
c. Wave A lags wave B by 15°.
d. Wave A leads wave B by 105°.
8. A phasor represents
a. the magnitude of a quantity
b. the magnitude and a quantity direction
c. the phase angle
d. the width of a quantity
9. The phasor current through a 200 ohm resistor assuming a voltage of 200Arms at an angle of
zero degree applied across it is
a. 1Arms at an angle of zero degree
b. 1Arms at an angle of 45 degree
c. 1Arms at an angle of 90 degree
d. 1Arms at an angle of 180 degree
10. A vector quantity has
a. Only magnitude
b. Only direction
c. Both (a) and (b)
d. None of these
11. The number of instantaneous values between zero and the peak value is
a. Zero
b. One
c. Eleven
d. Infinity
12. If the rms voltage drop across a 15 k resistor is 16 V, the peak current through the resistor is
a. 1.5 mA
b. 15 mA
c. 1 mA
d. 10 mA
13. If Power factor = Cos θ = 1, it means that _____________.
a. Input = Output
b. PIN = POUT
c. The circuit is resistive only
d. The angle (θ) between Voltage and Current is Zero.
14. Using P=VI Cos φ Formula, We Can Find_______.
a. Power of Single phase Circuit.
b. Voltage of Single Phase Circuit
c. Current of Single phase Circuit.
d. Power Factor of Single Phase Circuit
e. All of the above
f. None of the above
15. Reciprocal of Power Factor = _________?
a. Q Factor
b. Demand Factor
c. Diversity Factor
d. Utilization Factor
16. The relationship between Impedance (Z) and Admittance(Y) is ___________ ?
a. Z=1/Y
b. Z=1+Y
c. Z=1-Y
d. Z=Y2
17. When an ac power is applied to a reactive load, then the voltage is
a. In phase with the current
b. 90 degree out of phase with the current
c. 180 degree out of phase with the current
d. 270 degree out of phase with the current
18. If the number of turns, area and current of an ac circuit is doubled then the new inductance
will be
a. Equal to the former
b. Twice of the former
c. Four times the former
d. Half of the former
19. When a sine wave has a frequency of 100 Hz in 12 s it goes through
a. 12 cycles
b. 1/100 cycle
c. 1,200 cycles
d. 120 cycles
20. For a series RLC circuit energized with sinusoidal voltage source of frequency 4 rad/s, the
applied voltage lags the current by an angle of tan-1
2. With L = 1H and C = 0.05 F, the value
of R is
a. 4. 0 Ω
b. 2.0 Ω
c. 1.0 Ω
d. 0.5 Ω
21. A two terminal black box contains a series combination of resistor and unknown two terminal
linear devices. As soon as the battery is connected to the black box the current is found to be
zero. The device is
a. Inductor
b. Capacitor
c. Resistor
d. Cannot be identified
22. When a sinusoidal voltage is applied across RL series circuit having R = XL , the phase angle
will be
a. 900
b. 450
lag
c. 450
lead
d. 900
lead
23. Unit of reactive power is
a. VA
b. Watt
c. VAR
d. Ohm
24. For an AC circuit, if v(t) = 160 sin (wt+ 10) and i (t) = 5 sin (wt – 20), then reactive power
absorbed by the circuit is
a. 100 VARs
b. 200 VARs
c. 300 VARs
d. 400 VARs
25. The voltage phasor of a circuit is 10∟150 V and the current phasor is 2∟-450 A. The active
and reactive powers in the circuit are
a. 10 W and 17.32 VAR
b. 5 W and 8.66 VAR
c. 20 W and 60 VAR
d. 20√2 W and 10√2 VAR
26. In an RLC circuit, supplied from an AC source, the reactive power is proportional to the
a. Average energy stored in the electric field
b. Average energy stored in the magnetic field
c. Sum of the energy stored in the electric field and that stored in the magnetic field
d. Difference between the average energy stored in the electric field and that stored in the
magnetic field
27. The quantity 12+9j represents the resistive and reactive components of the current drawn by
an AC circuit. The phase angle between the applied voltage and current is
a. 41.40
b. 53.130
c. 36.870
d. 48.60
28. Real part of admittance is ………. And the imaginary part is ……….
a. Impedance, resistance
b. Resistance, impedance
c. Susceptance, inductance
d. Conductance, susceptance
29. In an AC circuit if voltage V = a + jb and the current I = c + jd, then the power is given by
a. ac + ad
b. ac + bd
c. bc – ad
d. bc + ad
30. The net electrical charge in an isolated system remains constant. This is known as
a. Law of conservation of charge
b. Coulomb`s first law
c. Coulomb`s second law
d. Law of conservation of energy
31. Peak to peak value of a sine wave is
a. Equal to the maximum or phase value of sine wave
b. Twice the maximum or phase value of sine wave
c. Half of the maximum or phase value of sine wave
d. Four times the maximum or phase value of sine wave
32. Power Factor (Cos θ) =_________?
a. kW/kVA
b. R/Z
c. The Cosine of angle between Current and voltage
d. All of the above
33. If Current and Voltage are 90 Degree Out of Phase, Then The Power (P) will be__________.
a. Infinite
b. Maximum
c. Normal
d. Minimum
e. Zero
34. In pure inductive circuit, the power is __________?
a. Infinite
b. Maximum
c. Normal
d. Minimum
e. Zero
35. In case of Capacitive circuit, Capacitance (C) is ___________ Proportional to the Capacitive
reactance (XC).
a. Directly
b. Inversely
c. No Effect
36. In pure capacitive circuit, the power is __________?
a. Infinite
b. Maximum
c. Normal
d. Minimum
e. Zero
37. Calculate all voltages, currents, and total power (Eline , Iline , Ephase(source) , Iphase(source),
Ephase(load), Iphase(load) ,Ptotal ) in this balanced Delta-Delta system where the source is having
a line voltage of 230 V and the load is having a impedance of 50 ohm
Ans : 230 V; 7.967 A; 230 V; 4.6 A; 230 V; 4.6 A; 3.174 kW
38. Calculate all voltages, currents, and total power (Eline , Iline , Ephase(source) , Iphase(source),
Ephase(load), Iphase(load) ,Ptotal ) in this balanced Star-Delta system where the source is having a
phase voltage of 230 V and the load is having a impedance of 580 ohm
Ans : 207.8 V; 0.621 A; 120 V; 0.621 A; 207.8 V; 0.358 A; 223.4 W
39. A current is said to be alternating when its
a. Magnitude and direction remains constant with time
b. Magnitude and direction changes with time
c. Magnitude only changes with time
d. Direction only changes with time
40. The most important advantage of using electrical energy in the form of AC is
a. The construction cost of AC generator per kW is lower than that of DC generator.
b. Conductor of smaller x-section is required in case of AC in comparison to DC for
carrying the same current
c. Less insulation is required in case of AC
d. Transformation of voltage is possible in case of AC only
41. The form factor for sinusoidal alternating current is
a. 1
b. 0
c. 1.11
d. 1.15
42. The RMS value of a sine wave is 100 A. Its peak value is
a. 70.7
b. 141
c. 150
d. 282.8
43. Two sinusoidal emfs are given as e1 = A sin (wt + π/4) and e2 = B sin (wt – π/6). The phase
difference between the two quantities in degrees is
a. 75
b. 105
c. 60
d. 15
44. The RMS value of the voltage u(t) = 3 + 4 cos (3t)
a. √17 V
b. 5 V
c. 7 V
d. ( 3 + 2√2 ) V
45. The RMS value of the resultant current in a wire which carries a DC current of 10 A and a
resulting sinusoidal alternating current of of peak value 20 A is
a. 14.1 A
b. 17.3 A
c. 22.4 A
d. 30.0 A
46. If two sinusoids of the same frequency but of different amplitudes and phase differences
are added, the resultant is a
a. Sinusoid of the same frequency
b. Sinusoid of double the original frequency
c. Sinusoid of half the original frequency
d. Non Sinusoid
47. Which of the following statements pertains to resistors only?
a. They oppose sudden changes in voltages
b. They can act as energy storage devices
c. They can dissipate desirable amount of power
d. None of the above
48. A boiler at home is switched on to the AC mains supplying power at 230 V, 50 Hz. The
frequency of instantaneous power is consumed
a. 0 Hz
b. 50 Hz
c. 100 Hz
d. 150 Hz
49. Pure inductive circuit
a. Consume some power on average
b. Does not consume power
c. Takes power from the line during some part of the cycle and then returns back during
other part of cycle
d. None of these
50. Purely inductive circuit takes power from the AC mains when
a. Both applied voltage and current increase
b. Both applied voltage and current decrease
c. Applied voltage decreases but current increases
d. Applied voltage increases but current decreases
51. Unit of inductive reactance is
a. Henry
b. milli-henry
c. wb
d. Ohm
52. A 10mH inductor carries a sinusoidal current of 1 A RMS at a frequency of 50 Hz. The
average power dissipated by the inductor is
a. 0 W
b. 0.25 W
c. 1 W
d. 0.5 W
53. A pure capacitance connected across 50 Hz, 230 V supply consumes 0.04 W. This
consumption is attributed to
a. Ohmic loss due to ohmic resistance of plates
b. Loss of energy in the dielectric
c. Capacitive reactance in ohms
d. Both (1) and (2)
54. A circuit component that opposes the change in the circuit voltage is
a. Resistance
b. Capacitance
c. Inductance
d. All of the above
55. The reactance offered by a capacitor to AC of frequency 50 Hz is 10 Ω. If the frequency is
increased to 100 Hz reactance becomes
a. 20 Ω
b. 5 Ω
c. 2.5 Ω
d. 40 Ω
56. A two terminal black box contains a series combination of a resistor and unknown twoterminal linear device. As soon as the battery is connected to the black box the current is
found to be zero. The device is
a. An inductor
b. A capacitor
c. A resistor
d. An unknown
57. The pf of a practical inductor is
a. Unity
b. Zero
c. Lagging
d. Leading
58. The power- factor of an ordinary electric bulb is
a. Zero
b. Unity
c. Slightly more than unity
d. Slightly less than unity
59. The power factor of an AC circuit is equal to
a. Cosine of the phase angle
b. Sine of the phase angle
c. Unity of a resistive circuit
d. Unity of a reactive circuit
60. The power factor of the AC circuit lies between
a. 0 and 1
b. -1 and 1
c. 0 and -1
d. None of these