1. ECE131 BASIC ELECTRICAL & ELECTRONICS ENGG
Unit-2
ECE131
BASIC ELECTRICAL & ELECTRONICS ENGG

2. Chapter 12
Alternating Current

3. Objectives After completing this chapter, you will be able to:
Describe how an AC voltage is produced with an AC generator (alternator)
Define alternation, cycle, hertz, sine wave, period, and frequency
Identify the parts of an AC generator (alternator)

4. Objectives (cont’d.) Define peak, peak-to-peak, effective, and rms
Explain the relationship between time and frequency
Identify and describe three basic nonsinusoidal waveforms
Describe how non-sinusoidal waveforms consist of the fundamental frequency and harmonics
Understand why AC is used in today’s society
Describe how an AC distribution system works

5. Generating Alternating Current
Figure 12-1A. Basic AC generator (alternator).
Figure 12-1B-F. AC generator inducing a voltage output.

6. Generating Alternating Current (cont’d.)
Figure Each cycle consists of a positive and a negative alternation.

7. Generating Alternating Current (cont’d.)
Figure The sinusoidal waveform, the most basic of the AC waveforms.

8. Generating Alternating Current (cont’d.)
Figure Voltage is removed from the armature of an
AC generator through slip rings.

9. AC Values
Figure The peak value of a sine wave is the point on the AC waveform having the greatest amplitude. The peak value occurs
during both the positive and the negative alternations of the waveform.

10. AC Values (cont’d.)
Figure The peak-to-peak value can be determined by adding the peak values of the two alternations.

11. AC Values (cont’d.) Effective value of a sine wave: Erms = 0.707Ep
where: Erms = rms or effective voltage value
Ep = maximum voltage of one alternation
Irms = 0.707Ip
where: Irms = rms or effective current value
Ip = maximum current of one alternation

12. Sample Question
The rms value of a half wave rectified symmetrical square wave current of 2 A is given by
0.707 A.
1 A.
1.414 A.
1.732 A.
Ans: C

13. AC Values (cont’d.)
Relationship between frequency and period:
f = 1/t
t = 1/f
where: f = frequency
t = period
What is the frequency of a sine wave with a time period of 0.05s?
Ans: 20 Hz
What is the period of a 60 Hz sine wave ?
Ans: s = 16.7 ms

14. Nonsinusoidal Waveforms
Figure Triangular waveform.
Figure Square waveform.
Figure Sawtooth waveform.

15. Summary AC is the most commonly used type of electricity
AC consists of current flowing in one direction and then reversing
One cycle per second is defined as a hertz
The waveform produced by an AC generator is called a sine wave

16. Summary (cont’d.)
The rms value of a sine wave is equal to times the peak value
The relationship between frequency and period is: f = 1/t
Basic non-sinusoidal waveforms include square, triangular, and saw-tooth

17. Chapter 14
Resistive AC Circuits

18. Objectives After completing this chapter, you will be able to:
Describe the phase relationship between current and voltage in a resistive circuit
Apply Ohm’s law to AC resistive circuits
Solve for unknown quantities in series AC resistive circuits
Solve for unknown quantities in parallel AC resistive circuits
Solve for power in AC resistive circuits

19. Basic AC Resistive Circuits
Figure A basic AC circuit consists of an
AC source, conductors, and a resistive load.

20. Basic AC Resistive Circuits (cont’d.)
Figure The voltage and current are in phase in a pure resistive circuit.

21. Series AC Circuits
Figure Simple series AC circuit.

22. Figure 14-4. The in-phase relationship of the voltage drops,
applied voltage, and current in a series AC circuit.

24. Parallel AC Circuits
Figure A simple parallel AC circuit.

25. Figure 14-6. The in-phase relationship of the applied voltage,
total current, and individual branch currents in a parallel AC circuit.

26. Sample Question

27. Power in AC Circuits
Figure The relationship of power, current, and voltage in a resistive AC circuit.

29. Summary
A basic AC circuit consists of an AC source, conductors, and a resistive load
The voltage and current are in phase in a pure resistive circuit
The effective value of AC current or voltage produces the same results as the equivalent DC voltage or current
Ohm’s law can be used with all effective values
AC voltage or current values are assumed to be the effective values if not otherwise specified

30. Capacitive AC Circuits
Chapter 15
Capacitive AC Circuits

31. Objectives After completing this chapter, you will be able to:
Describe the phase relationship between current and voltage in a capacitive AC circuit
Determine the capacitive reactance in an AC capacitive circuit
Describe how resistor-capacitor networks can be used for filtering, coupling, and phase shifting
Explain how low-pass and high-pass RC filters operate

32. Capacitors in AC Circuits
Capacitive reactance
Opposition a capacitor offers to the applied AC voltage
Represented by Xc
Measured in ohms
Figure Note the out-of-phase relationship between the current and
the voltage in a capacitive AC circuit. The current leads the applied voltage.

33. Capacitors in AC Circuits (cont’d.)
Formula for capacitive reactance:
Where: π = pi, the constant 3.14
f = frequency in hertz
C = capacitance in farads

34. Question 1 Which of the following capacitors is polarized? ceramic
mica
plastic-film
electrolytic
Ans: D

35. Question 2
A sine wave voltage is applied across a capacitor. When the frequency of the voltage is decreased, the current
ceases
remains constant
increases
decreases
Ans: D

37. Applications of Capacitive Circuits
Figure RC low-pass filter.

38. Figure 15-3. Frequency response of an RC low-pass filter.

39. Applications of Capacitive Circuits (cont’d.)
Figure RC high-pass filter.

40. Figure 15-5. Frequency response of an RC high-pass filter.

41. Applications of Capacitive Circuits (cont’d.)
Figure RC decoupling network.

42. Applications of Capacitive Circuits (cont’d.)
Figure RC coupling network.

43. Sample Question 4
A capacitor and a resistor are connected in series to a sine wave generator. The frequency is set so that the capacitive reactance is equal to the resistance and, thus, an equal amount of voltage appears across each component. If the frequency is increased
VC> VR
VR and VC = 0
VR = VC
VR > VC
Ans: D

44. Applications of Capacitive Circuits (cont’d.)
Figure Leading output phase-shift network.
The output voltage leads the input voltage.

45. Applications of Capacitive Circuits (cont’d.)
Figure Lagging output phase-shift network.
The voltage across the capacitor lags the applied voltage.

46. Applications of Capacitive Circuits (cont’d.)
Figure Cascaded RC phase-shift networks.

47. Summary
When an AC voltage is applied to a capacitor, it gives the appearance of current flow
The capacitor charging and discharging represents current flow
The current leads the applied voltage by 90 degrees in a capacitive circuit
Capacitive reactance is the opposition a capacitor offers to the applied voltage
Capacitive reactance is a function of the frequency of the applied AC voltage and the capacitance:
RC networks are used for filtering, coupling, and phase shifting

48. Chapter 16
Inductive AC Circuits

49. Objectives After completing this chapter, you will be able to:
Describe the phase relationship between current and voltage in an inductive AC circuit
Determine the inductive reactance in an AC circuit
Explain impedance and its effect on inductive circuits
Describe how an inductor-resistor network can be used for filtering and phase shifting
Explain how low-pass and high-pass inductive circuits operate

50. Inductors in AC Circuits
Figure The applied voltage and the induced voltage are
180 degrees out of phase with each other in an inductive circuit.

51. Inductors in AC Circuits (cont’d.)
Figure The current lags the applied voltage in an AC inductive circuit.

52. Inductors in AC Circuits (cont’d.)
Inductive reactance
Opposition to current flow offered by an inductor in an AC circuit
Expressed by the symbol XL
Measured in ohms
where: π = pi or 3.14
f = frequency in hertz
L = inductance in Henries

53. Inductors in AC Circuits (cont’d.)
Impedance
Total opposition to current flow by both inductor and resistor
Vector sum of the inductive reactance and the resistance in the circuit

54. Sample Question
When the frequency of the source voltage decreases, the impedance of a parallel RC circuit
increases
decreases to zero
does not change
decreases
Ans: A

55. Applications of Inductive Circuits
Figure RL filters.

56. LCR Circuits
Parallel R-L-C Circuit
Series R-L-C Circuits