ac fundamentals sinusoidal representation rms peak resonance polyphase systems star delta three phase power - One Line Questions

1. In a balanced three-phase system, what is the phase difference between the voltages of any two phases? — 120 degrees
2. What is the form factor for a sinusoidal waveform? — 1.11
3. What is the crest factor for a sinusoidal waveform? — 1.414
4. An AC current is given by I(t) = 10 sin(ωt + π/4) A. What is the peak current? — 10 A
5. A circuit has a resistance of 10 Ω and an inductive reactance of 10 Ω. What is its impedance at 50 Hz? — 14.14 Ω
6. If the peak voltage of a sinusoidal AC supply is 170 V, what is its RMS voltage? — 120 V
7. 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? — 11.55 A
8. A balanced three-phase load connected in star has a phase voltage of 230 V. What is the line voltage? — 398.4 V
9. An AC voltage is given by V(t) = 311 sin(377t) V. What is the RMS voltage? — 220 V
10. 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? — 230 V
11. If the RMS current in a circuit is 5 A, what is the peak current? — 7.07 A
12. What is the angular frequency (ω) of an AC supply with a frequency of 50 Hz? — 314 rad/s
13. In a three-phase induction motor, the rotating magnetic field is produced by: — A three-phase AC supply
14. What is a 'star' connection in a three-phase system? — One end of each phase winding is connected to a common neutral point
15. What is the condition for resonance in a series RLC circuit? — Capacitive reactance equals inductive reactance
16. What is the primary characteristic of a sinusoidal alternating current (AC) waveform? — Smooth, continuous oscillation over time
17. In a three-phase system, the neutral wire is typically present in which connection type? — Star
18. What is the resonant frequency (f_r) formula for a series RLC circuit? — f_r = 1 / (2π√(LC))
19. In a star-connected system, what is the relationship between line current (I_L) and phase current (I_ph)? — I_L = I_ph
20. In a delta-connected system, what is the relationship between line current (I_L) and phase current (I_ph)? — I_L = I_ph * sqrt(3)
21. In a parallel RLC circuit, resonance occurs when: — Inductive reactance equals capacitive reactance
22. What happens to the current at resonance in a series RLC circuit, assuming constant voltage? — It is at its maximum value
23. 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? — It is reduced by a factor of four
24. If a star-connected load is unbalanced, what is the likely consequence for the neutral wire? — It will carry a significant current, potentially causing voltage instability
25. A lagging power factor indicates that the current: — Lags the voltage
26. At resonance in a series RLC circuit, what is the impedance of the circuit? — Minimum possible value (equal to resistance)
27. At resonance in a parallel RLC circuit, the impedance is: — Maximum
28. A polyphase system typically refers to systems with how many phases? — Three or more
29. What is a 'delta' connection in a three-phase system? — The windings are connected end-to-end to form a closed loop or triangle
30. What is the total power (P_total) consumed in a balanced three-phase system? — P_total = sqrt(3) * V_L * I_L * cos(θ)
31. For a sinusoidal waveform, the form factor is defined as the ratio of: — RMS value to average value
32. What is the quality factor (Q) of a resonant circuit? — Ratio of stored energy to energy dissipated per cycle
33. The power factor (cos θ) in an AC circuit represents the ratio of: — Real power to apparent power
34. Which parameter determines the resonant frequency in an LC circuit? — Inductance and Capacitance
35. The crest factor of a sinusoidal waveform is the ratio of: — Peak value to RMS value
36. What is the main advantage of a three-phase power system over a single-phase system? — Requires less conductor material for the same power transmission
37. In the sinusoidal representation of an AC voltage, what does the term 'amplitude' refer to? — The maximum instantaneous value reached by the waveform
38. What is the RMS (Root Mean Square) value of a sinusoidal AC waveform? — The equivalent DC value that would produce the same heating effect
39. What is the bandwidth (BW) of a resonant circuit? — The range of frequencies over which the power is at least half the maximum power
40. The frequency of AC power in North America is typically 60 Hz. What does this frequency represent? — The number of cycles per second
41. What is the 'peak-to-peak' voltage of a sinusoidal AC waveform? — The difference between the maximum positive and maximum negative instantaneous values
42. In an AC circuit, what is 'phase angle'? — The difference in time or position between two oscillating waveforms of the same frequency
43. What is the purpose of a neutral wire in a star-connected three-phase system? — To provide a return path for unbalanced currents and maintain voltage stability
44. What is the primary purpose of using polyphase systems in power generation and distribution? — For efficient power transmission and operation of motors
45. In a star-connected system, what is the relationship between line voltage (V_L) and phase voltage (V_ph)? — V_L = V_ph * sqrt(3)
46. In a delta-connected system, what is the relationship between line voltage (V_L) and phase voltage (V_ph)? — V_L = V_ph
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)? — V_rms = V_m / sqrt(2)
48. What is the unit of real power in an AC circuit? — Watt (W)
49. Which of the following is a form of apparent power in an AC circuit? — Volt-Ampere (VA)
50. What is the unit of reactive power in an AC circuit? — Volt-Ampere Reactive (VAR)
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