In this article, we shared the AC fundamentals objective questions and answers for electrical and electronics engineers.
AC Fundamentals Objective Questions
The below list provides all the multiple-choice questions related to AC fundamentals.
Answers are available at the bottom of the article.
1. In a parallel RC circuit, the current always ____the applied voltage.
| A) | Leads |
| B) | Lags |
| C) | None of these answers |
| D) | Remains in phase with |
2. The shunt element of the prototype high pass filter is
| A) | Inductive |
| B) | Resistive |
| C) | Combination of L and C |
| D) | Capacitive |
3. What inductance will give the same reactance as a capacitor of 2 μF when both are at 50 Hz?
| A) | 15 H |
| B) | 5 H |
| C) | 20 H |
| D) | 10 H |
4. Which of the following is not a non-linear element?
| A) | Heater coil |
| B) | Diode |
| C) | Electric arc with unlike electrodes |
| D) | Transistor |
5. The dual of a loop is
| A) | Mesh |
| B) | Twig |
| C) | Node pair |
| D) | Tree |
6. The series element of a band-stop filter is
| A) | Inductive |
| B) | The parallel combination of L and C |
| C) | Capacitive |
| D) | Series combination of L and C |
7. In the RLC circuit ontaining R = 4.5ω L = 0.06 H,C = 0.6 μF the power factor will be
| A) | Zero |
| B) | Lagging |
| C) | Unity |
| D) | Leading |
8. The r.m.s. value of a sine wave is 100A. Its peak value is
| A) | 150 A |
| B) | 282.8 A |
| C) | 70.7 A |
| D) | 141.4 A |
9. The dual of a link is
| A) | Tree branch |
| B) | Twig |
| C) | Node |
| D) | Loop |
10. Selectivities of different resonance circuits are compared in terms of their
| A) | Impedances |
| B) | Reactances |
| C) | Frequencies |
| D) | Band widths |
11. Power factor of the following circuit will be zero
| A) | Inductance |
| B) | Resistance |
| C) | Both Inductance and Capacitance |
| D) | Capacitance |
12. In an RLC series circuit if voltage V across the circuit is reduced to half the current I will change to
| A) | 5/8 I |
| B) | 3/4 I |
| C) | 2 I |
| D) | I/2 |
13. When an alternating current passes through an ohmic resistance the electrical power converted into heat is
| A) | True power |
| B) | Reactive power |
| C) | None of these answers |
| D) | Apparent power |
14. The period of a wave is
| A) | Time required to complete one cycle |
| B) | Expressed in amperes |
| C) | The same as the frequency |
| D) | None of these answers |
15. Ohm is the unit of all of the following except
| A) | Capacitance |
| B) | Inductive reactance |
| C) | Capacitive reactance |
| D) | Resistance |
16. The time constant of a series R-C circuit is given by
| A) | R/C |
| B) | R2C |
| C) | RC |
| D) | RC2 |
17. The voltage of the domestic supply is 220 V.
| A) | Peak value |
| B) | Average value |
| C) | Mean value |
| D) | r.m.s. value |
18. In an A.C. circuit I sin Φ is called
| A) | Any of these answers |
| B) | Wattless component |
| C) | None of these answers |
| D) | Active component |
19. The time period of a sine wave is 1/50 seconds. Its frequency is
| A) | 50 Hz |
| B) | 40 Hz |
| C) | 30 Hz |
| D) | 20 Hz |
20. In an A.C. circuit laminated iron is invariably used in order to
| A) | Make assembly cheap and easier |
| B) | Reduce circuit permeability |
| C) | Increase heat radiation |
| D) | Reduce eddy current loss |
21. The transient currents are associated with the
| A) | Changes in the stored energy in the inductors and capacitors |
| B) | Resistance of the circuit |
| C) | Applied voltage to the circuit |
| D) | The impedance of the current |
22. The ratio of active power to apparent power is known as the ____ factor.
| A) | Demand |
| B) | Power |
| C) | Form |
| D) | Load |
23. Which of the following waves has the highest value of peak factor?
| A) | Sine wave |
| B) | Half wave rectifier sine wave |
| C) | Square wave |
| D) | Triangular wave |
24. In a pure resistive circuit
| A) | Current can lead or lag the voltage by 90° |
| B) | Current lags behind the voltage by 90° |
| C) | Current is in phase with the voltage |
| D) | Current leads the voltage by 90° |
25. The frequency of domestic power supply in India is
| A) | 100 Hz |
| B) | 200 Hz |
| C) | 50 Hz |
| D) | 60 Hz |
26. The peak value of a sine wave is 200 V. Its average value is
| A) | 127.4V |
| B) | 200 V |
| C) | 282.8V |
| D) | 141.4V |
27. Capacitive reactance is more when
| A) | Capacitance is less and frequency of supply is less |
| B) | Capacitance is less and frequency of supply is more |
| C) | Capacitance is more and frequency of supply is less |
| D) | Capacitance is more and frequency of supply is more |
28. The power factor of a D.C. circuit is always
| A) | Unity |
| B) | Less than unity Capacitors for power factor correction are rated in Capacitors for power factor correction are rated in |
| C) | Greater than Unity |
| D) | Zero |
29. Higher the Q of a series circuit
| A) | Narrower its pass band |
| B) | Sharper its resonace |
| C) | Greater its band width |
| D) | Broader its resonance curve |
30. The negative maximum of a cosine wave occurs at
| A) | 90 |
| B) | 45 |
| C) | 180 |
| D) | 30 |
31. In a series resonant circuit, the impedance of the circuit is
| A) | Maximum |
| B) | Zero |
| C) | None of these answers |
| D) | Minimum |
32. The power taken by a 3-Φ load is given by the expression
| A) | √3 VL IL sinΦ |
| B) | √3 VL IL cosΦ |
| C) | 3 VL IL sinΦ |
| D) | 3 VL IL cosΦ |
33. The form factor of D.C. supply voltage is always
| A) | Zero |
| B) | 0.5 |
| C) | Infinite |
| D) | Unity |
34. The r.m.s. value and the mean value is the same in the case of
| A) | Triangular wave |
| B) | Square wave |
| C) | Sine wave |
| D) | Half wave rectified sine wave |
35. For a sine wave with peak value Imax the r.m.s. value is
| A) | 0.9 Imax |
| B) | 0.5 Imax |
| C) | 1.414 Imax |
| D) | 0.707 Imax |
36. Inductance affects the direct current flow
| A) | Only at the time of turning on |
| B) | At all the time of operation |
| C) | At the time of turning on and off |
| D) | Only at the time of turning off |
37. While drawing a vector diagram for a series circuit the reference vector is
| A) | Current |
| B) | Phase angle |
| C) | Power |
| D) | Voltage |
38. For a sine wave with a peak value Emax the average value is
| A) | 0.434 Emax |
| B) | 0.636 Emax |
| C) | 0.707 Emax |
| D) | 1.414 Emax |
39. Poor power factor results in all of the following EXCEPT.
| A) | Reduction in load handling capacity of electrical system |
| B) | Reduction in power losses |
| C) | Overloading of altemators |
| D) | Overloading of transformers |
40. A heater is rated as 230 V, 10 KW, AC. The value 230 V refers to
| A) | Peak voltage |
| B) | Average voltage |
| C) | r.m.s. voltage |
| D) | None of these answers |
41. The form factor is the ratio of
| A) | Peak value to r.m.s. value |
| B) | Average value to r.m.s. value |
| C) | None of these answers |
| D) | r.m.s. value to average value |
42. For the same peak value of voltage which waveform will have the least r.m.s. value?
| A) | Full wave rectified sine wave |
| B) | Triangular wave |
| C) | Square wave |
| D) | Sine wave |
43. Skin effect occurs when a conductor carries the current at ____ frequencies.
| A) | Medium |
| B) | Very low |
| C) | Low |
| D) | High |
44. Form factor is the ratio of
| A) | Average value/peak value |
| B) | Average value/r.m.s. value |
| C) | r.m.s. value/peak value |
| D) | r.m.s. value/average value |
45. The power is measured in terms of decibels in the case of
| A) | Auto-transformers |
| B) | Current transformers |
| C) | Transformers |
| D) | Electronic equipment |
46. A sine wave of voltage varies from zero to a maximum of 200 V. How much is the voltage at the instant of 30° of the cycle?
| A) | 173.2 V |
| B) | 100V |
| C) | 82.8V |
| D) | 50V |
47. The power consumed in a circuit element will be least when the phase difference between the current and voltage
| A) | 60° |
| B) | 90° |
| C) | 180° |
| D) | 0° |
48. The power factor of a series R-L-C circuit at its half-power points is
| A) | Unity |
| B) | Lagging |
| C) | Lagging or leading |
| D) | Leading |
49. For the full-wave rectified sine wave the r.m.s. value is
| A) | Zero |
| B) | 0.318 Imax |
| C) | 0.707 Imax |
| D) | 0.636 Imax |
50. In a purely inductive circuit
| A) | None of these answers |
| B) | Actual power is zero |
| C) | Reactive power is zero |
| D) | Apparent power is zero |
51. The r.m.s. value of pure cosine function is
| A) | 0.707 of peak value |
| B) | Same as peak value |
| C) | Zero |
| D) | 0.5 of peak value |
52. Which of the following statement is incorrect?
| A) | Current source is a passive element |
| B) | Conductance is a passive element |
| C) | Resistance is a passive element |
| D) | Voltage source is an active element |
53. The reflection co-efficient of the simplest standing wave is
| A) | 1 |
| B) | Infinity |
| C) | Zero |
| D) | +1 |
54. At very low frequencies a series RC circuit behaves as almost purely____
| A) | Resistive |
| B) | Capacitive |
| C) | Inductive |
| D) | None of these answers |
55. The double energy transient occurs in the
| A) | Purely inductive circuit |
| B) | R-L circuit |
| C) | R-C circuit |
| D) | R-L-C circuit |
56. If resistance is 20 ω and inductance is 2H in an RL series circuit, then the time constant of this circuit will be
| A) | 10 S |
| B) | 0.001 S |
| C) | 100 S |
| D) | 0.1 S |
57. The r.m.s. value of a sinusoidal A.C. current is equal to its value at an angle of____ degrees
| A) | 30 |
| B) | 90 |
| C) | 45 |
| D) | 60 |
58. The unit of frequency of an A.C. signal is
| A) | Cycle-sec |
| B) | Hertz |
| C) | Hertz/sec |
| D) | Cycle |
59. The capacitors for power factor correction are rated in terms of
| A) | VA |
| B) | Voltage |
| C) | kW |
| D) | kVAR |
60. In a series resonant circuit, the impedance of the circuit is
| A) | Minimum |
| B) | Maximum |
| C) | Infinite |
| D) | Zero |
61. At____ frequencies the parallel R-L circuit behaves as purely resistive.
| A) | Low |
| B) | High |
| C) | Very high |
| D) | Very low |
62. Two sinusoidal quantities are said to be phase quadrature when their phase difference is
| A) | 90° |
| B) | 45° |
| C) | 30° |
| D) | 0 |
63. How much r.m.s. current does a 300 W. 200V bulb take from the 200 V, 50 Hz power line?
| A) | 3A |
| B) | 2A |
| C) | 0.5A |
| D) | 1.5 A |
64. The power factor of the incandescent bulb is
| A) | 0.8 lagging |
| B) | Zero |
| C) | Unity |
| D) | 0.8 leading |
65. Form factor for a sine wave is
| A) | 1.414 |
| B) | 0.637 |
| C) | 0.707 |
| D) | 1.11 |
66. In a circuit containing R, L, and C, power loss can take place
| A) | All of these answers |
| B) | R only |
| C) | C only |
| D) | L only |
67. For the same peak value, which of the following wave has the least mean value?
| A) | Half wave rectified sine wave |
| B) | Sine wave |
| C) | Triangular wave |
| D) | Square wave |
68. Power factor of an electric bulb is
| A) | Zero |
| B) | Unity |
| C) | Leading |
| D) | Lagging |
69. The r.m.s. value of a half-wave rectified current is 100 A. Its value for full-wave rectification would be ____ amperes.
| A) | 200 |
| B) | 200/π |
| C) | 40/π |
| D) | 141.4 |
70. The product of apparent power and cosine of the phase angle between circuit voltage and current is
| A) | Reactive power |
| B) | Instantaneous power |
| C) | Volt-amperes |
| D) | True power |
71. A parallel resonant circuit can be used
| A) | As a high impedance |
| B) | To reject a small band of frequencies |
| C) | To amplify certain frequencies |
| D) | Both As a high impedance and To reject a small band of frequencies |
72. A coil with large distributed capacitance has a
| A) | High resonant frequency |
| B) | Low resistance |
| C) | Low quality factor |
| D) | Low resonant frequency |
73. Power factor of an inductive circuit is usually improved by connecting the capacitor to it in
| A) | Series |
| B) | Either Parallel or Series |
| C) | None of these answers |
| D) | Parallel |
74. A network is said to be non-linear if it does not satisfy
| A) | Associative condition |
| B) | Homogeneity condition |
| C) | Both Homogeneity condition and Superposition condition |
| D) | Superposition condition |
75. In the A.C. circuit the power curve is a sine wave having
| A) | None of these answers |
| B) | Half the frequency of the voltage |
| C) | Double the frequency of the voltage |
| D) | Same frequency as that of voltage |
76. The best place to install a capacitor is
| A) | Far away from the inductive load |
| B) | Any where |
| C) | Very near to inductive load |
| D) | Across the terminals of the inductive load |
77. All the rules and laws of D.C. circuit also supply to A.C. circuit containing
| A) | Resistance only |
| B) | All of these answers |
| C) | Capacitance only |
| D) | Inductance only |
78. Which of the following circuit component opposes the change in the circuit voltage
| A) | Capacitance |
| B) | Inductance |
| C) | Conductance |
| D) | Resistance |
79. Power factor of the following circuit will be unity
| A) | Resistance |
| B) | Both Inductance and Capacitance |
| C) | Capacitance |
| D) | Inductance |
80. In an A.C. circuit, a low value of kVAR compared with kW indicates
| A) | High power factor |
| B) | Low efficiency |
| C) | Maximum Load current |
| D) | Unity power factor |
81. A resonance curve for a series circuit is a plot of frequency versus
| A) | Current |
| B) | Voltage |
| C) | Reactance |
| D) | Impedance |
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