ac fundamentals sinusoidal representation rms peak resonance polyphase systems star delta three phase power - Question Bank

1. Which parameter determines the resonant frequency in an LC circuit?
A) Resistance
B) Inductance and Capacitance
C) Voltage
D) Current
2. If a star-connected load is unbalanced, what is the likely consequence for the neutral wire?
A) It will carry zero current
B) It will carry a current equal to the average of the phase currents
C) It will carry a significant current, potentially causing voltage instability
D) It will carry a current that is the vector sum of the phase currents
3. What is the primary purpose of using polyphase systems in power generation and distribution?
A) To increase voltage levels
B) To reduce harmonic distortion
C) For efficient power transmission and operation of motors
D) To simplify circuit analysis
4. In a three-phase induction motor, the rotating magnetic field is produced by:
A) A single-phase AC supply
B) A DC supply
C) A three-phase AC supply
D) The rotor current
5. What is the crest factor for a sinusoidal waveform?
A) 1.11
B) 1.414
C) 0.707
D) 2
6. The crest factor of a sinusoidal waveform is the ratio of:
A) RMS value to average value
B) Peak value to RMS value
C) Average value to RMS value
D) Peak value to average value
7. What is the form factor for a sinusoidal waveform?
A) 1.11
B) 1.414
C) 0.707
D) 2
8. For a sinusoidal waveform, the form factor is defined as the ratio of:
A) Peak value to RMS value
B) RMS value to average value
C) Average value to peak value
D) Peak value to average value
9. What is the bandwidth (BW) of a resonant circuit?
A) The frequency at which resonance occurs
B) The range of frequencies over which the power is at least half the maximum power
C) The product of resistance and capacitance
D) The inverse of the time constant
10. A circuit has a resistance of 10 Ω and an inductive reactance of 10 Ω. What is its impedance at 50 Hz?
A) 10 Ω
B) 14.14 Ω
C) 20 Ω
D) 0 Ω
11. What happens to the total power delivered by a three-phase system if the voltage is reduced by half, keeping the current and power factor constant?
A) It remains the same
B) It is reduced by half
C) It is reduced by a factor of four
D) It is doubled
12. If a three-phase motor is connected to a star-connected supply, and the line voltage is 400 V, what is the voltage across each phase winding?
A) 400 V
B) 230 V
C) 692 V
D) 133 V
13. What is the purpose of a neutral wire in a star-connected three-phase system?
A) To carry the sum of the phase currents under balanced conditions
B) To provide a return path for unbalanced currents and maintain voltage stability
C) To increase the line voltage
D) To reduce the phase current
14. In a three-phase system, the neutral wire is typically present in which connection type?
A) Delta
B) Star
C) Both Star and Delta
D) Neither Star nor Delta
15. A balanced three-phase load connected in star has a phase voltage of 230 V. What is the line voltage?
A) 230 V
B) 132.8 V
C) 398.4 V
D) 400 V
16. A balanced three-phase load connected in delta draws a line current of 20 A. What is the current through each phase of the load?
A) 20 A
B) 11.55 A
C) 34.64 A
D) 6.67 A
17. What is the quality factor (Q) of a resonant circuit?
A) Ratio of resistance to reactance
B) Ratio of stored energy to energy dissipated per cycle
C) Ratio of voltage to current
D) Ratio of frequency to bandwidth
18. At resonance in a parallel RLC circuit, the impedance is:
A) Minimum
B) Maximum
C) Zero
D) Equal to resistance
19. In a parallel RLC circuit, resonance occurs when:
A) Inductive reactance equals resistance
B) Capacitive reactance equals resistance
C) Inductive reactance equals capacitive reactance
D) The impedance is at its minimum
20. What is the angular frequency (ω) of an AC supply with a frequency of 50 Hz?
A) 50 rad/s
B) 100 rad/s
C) 157 rad/s
D) 314 rad/s
21. If the RMS current in a circuit is 5 A, what is the peak current?
A) 5 A
B) 3.54 A
C) 7.07 A
D) 10 A
22. An AC current is given by I(t) = 10 sin(ωt + π/4) A. What is the peak current?
A) 10 A
B) 5 A
C) 7.07 A
D) 14.14 A
23. An AC voltage is given by V(t) = 311 sin(377t) V. What is the RMS voltage?
A) 311 V
B) 220 V
C) 440 V
D) 155.5 V
24. A lagging power factor indicates that the current:
A) Leads the voltage
B) Lags the voltage
C) Is in phase with the voltage
D) Is 180 degrees out of phase with the voltage
25. The power factor (cos θ) in an AC circuit represents the ratio of:
A) Reactive power to apparent power
B) Real power to apparent power
C) Apparent power to real power
D) Real power to reactive power
26. What is the unit of reactive power in an AC circuit?
A) Watt (W)
B) Volt-Ampere (VA)
C) Volt-Ampere Reactive (VAR)
D) Farad (F)
27. What is the unit of real power in an AC circuit?
A) Volt-Ampere (VA)
B) Watt (W)
C) Volt-Ampere Reactive (VAR)
D) Ohm (Ω)
28. Which of the following is a form of apparent power in an AC circuit?
A) Watt (W)
B) Volt-Ampere Reactive (VAR)
C) Volt-Ampere (VA)
D) Joule (J)
29. What is the total power (P_total) consumed in a balanced three-phase system?
A) P_total = 3 * V_ph * I_ph * cos(θ)
B) P_total = sqrt(3) * V_L * I_L * cos(θ)
C) P_total = V_L * I_L * cos(θ)
D) P_total = 3 * V_L * I_L * cos(θ)
30. In a delta-connected system, what is the relationship between line current (I_L) and phase current (I_ph)?
A) I_L = I_ph
B) I_L = I_ph / sqrt(3)
C) I_L = I_ph * sqrt(3)
D) I_L = 2 * I_ph
31. In a delta-connected system, what is the relationship between line voltage (V_L) and phase voltage (V_ph)?
A) V_L = V_ph
B) V_L = V_ph / sqrt(3)
C) V_L = V_ph * sqrt(3)
D) V_L = 2 * V_ph
32. In a star-connected system, what is the relationship between line current (I_L) and phase current (I_ph)?
A) I_L = I_ph
B) I_L = I_ph / sqrt(3)
C) I_L = I_ph * sqrt(3)
D) I_L = 2 * I_ph
33. In a star-connected system, what is the relationship between line voltage (V_L) and phase voltage (V_ph)?
A) V_L = V_ph
B) V_L = V_ph / sqrt(3)
C) V_L = V_ph * sqrt(3)
D) V_L = 2 * V_ph
34. What is a 'delta' connection in a three-phase system?
A) One end of each phase winding is connected to a common neutral point
B) All three phase windings are connected in series
C) The windings are connected end-to-end to form a closed loop or triangle
D) The windings are connected in parallel
35. What is a 'star' connection in a three-phase system?
A) All three phase windings are connected in series
B) One end of each phase winding is connected to a common neutral point
C) All three phase windings are connected in parallel
D) The windings are connected in a triangular configuration
36. In a balanced three-phase system, what is the phase difference between the voltages of any two phases?
A) 0 degrees
B) 60 degrees
C) 90 degrees
D) 120 degrees
37. What is the main advantage of a three-phase power system over a single-phase system?
A) Simpler transformer design
B) Lower transmission losses for the same amount of power
C) Requires less conductor material for the same power transmission
D) Easier voltage regulation
38. A polyphase system typically refers to systems with how many phases?
A) One
B) Two
C) Three or more
D) Exactly two
39. What happens to the current at resonance in a series RLC circuit, assuming constant voltage?
A) It is at its minimum value
B) It is at its maximum value
C) It becomes zero
D) It becomes reactive
40. What is the resonant frequency (f_r) formula for a series RLC circuit?
A) f_r = 1 / (2πRC)
B) f_r = 1 / (2πRL)
C) f_r = 1 / (2π√(LC))
D) f_r = R / (2π√(LC))
41. At resonance in a series RLC circuit, what is the impedance of the circuit?
A) Maximum possible value
B) Minimum possible value (equal to resistance)
C) Infinite value
D) Zero value
42. What is the condition for resonance in a series RLC circuit?
A) Capacitive reactance equals resistance
B) Inductive reactance equals resistance
C) Capacitive reactance equals inductive reactance
D) Resistance equals the sum of inductive and capacitive reactances
43. In an AC circuit, what is 'phase angle'?
A) The RMS value of the voltage
B) The difference in time or position between two oscillating waveforms of the same frequency
C) The total power consumed by the circuit
D) The frequency of the AC supply
44. The frequency of AC power in North America is typically 60 Hz. What does this frequency represent?
A) The number of cycles per second
B) The time period of one cycle
C) The number of voltage reversals per minute
D) The phase difference between conductors
45. What is the 'peak-to-peak' voltage of a sinusoidal AC waveform?
A) The RMS value
B) The maximum instantaneous value
C) The difference between the maximum positive and maximum negative instantaneous values
D) The average value over half a cycle
46. If the peak voltage of a sinusoidal AC supply is 170 V, what is its RMS voltage?
A) 120 V
B) 170 V
C) 240 V
D) 85 V
47. For a sinusoidal voltage V(t) = V_m sin(ωt), what is the relationship between the RMS value (V_rms) and the peak value (V_m)?
A) V_rms = V_m
B) V_rms = V_m / 2
C) V_rms = V_m / sqrt(2)
D) V_rms = V_m * sqrt(2)
48. What is the RMS (Root Mean Square) value of a sinusoidal AC waveform?
A) The average value over a full cycle
B) The maximum instantaneous value
C) The equivalent DC value that would produce the same heating effect
D) The peak-to-peak value
49. In the sinusoidal representation of an AC voltage, what does the term 'amplitude' refer to?
A) The average value over a full cycle
B) The maximum instantaneous value reached by the waveform
C) The frequency of oscillation
D) The time taken for one complete cycle
50. What is the primary characteristic of a sinusoidal alternating current (AC) waveform?
A) Constant voltage magnitude
B) Varying frequency
C) Smooth, continuous oscillation over time
D) Abrupt changes in direction
All Question Banks
E-Book ac fundamentals sinusoidal representation rms peak resonance polyphase systems star delta three phase power One Line Questions ac fundamentals sinusoidal representation rms peak resonance polyphase systems star delta three phase power Online Test ac fundamentals sinusoidal representation rms peak resonance polyphase systems star delta three phase power