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Section 2

Section 2. AC Circuits. Chapter 12. Alternating Current. Objectives After completing this chapter, the student should be able to: Describe how an AC voltage is produced with an AC generator. Define alternation, cycle, hertz, sine wave, period, and frequency.

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Section 2

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  1. Section 2 AC Circuits

  2. Chapter 12 Alternating Current

  3. Objectives • After completing this chapter, the student should be able to: • Describe how an AC voltage is produced with an AC generator. • Define alternation, cycle, hertz, sine wave, period, and frequency. • Identify the parts of an AC generator. • Define peak, peak-to-peak, effective, and rms.

  4. Explain the relationship between time and frequency. • Identify and describe three basic nonsinusoidal waveforms. • Describe how nonsinusoidal waveforms consist of the fundamental frequency and harmonics. • Understand why AC is used in today’s society. • Describe how an AC distribution system works. • Identify and use the math associated with AC.

  5. Nikola Tesla • The father of Alternating Current (AC).

  6. AC generator produces an alternating voltage using the principles of electromagnetic induction.

  7. ( B ) No voltage is induced when the conductor is moved parallel to the lines of force.

  8. ( C ) As the loop is rotated, it passes through more lines of force, and the maximum voltage is induced when the loop is at right angles to the lines of force.

  9. ( D ) As the loop continues to rotate, fewer lines of force are cut and the induced voltage decreases.

  10. ( E ) Again, the maximum voltage is induced when the loop is at right angles to the lines of force.

  11. ( F ) As the loop returns to its original position, the induced voltage returns to zero.

  12. Cycle • Each time the AC generator completes one revolution. • Its output voltage is referred to as one cycle of output voltage. • It produces one cycle of output current in a complete circuit.

  13. The two halves of a cycle are called alternations. • Two complete alternations make up a cycle. • One cycle per second is called a hertz (Hz).

  14. Armature • The rotating loop of wire. • Sinusoidal waveform • Also called a sine wave. • The waveform produced by an AC generator. • Can be produced by mechanical and electronic methods. • Identical to the trigonometric sine function.

  15. AC values • Each point on a sine wave has two numbers associated with it. • The degree of rotation. • The angle to which the armature has turned. • The amplitude. • The maximum departure of the value of an alternating current or wave from the average value.

  16. Peak value • The absolute value of the point on the waveform with the greatest amplitude.

  17. Peak-to-peak value • The vertical distance between two peaks.

  18. Effective value • The amount that produces the same degree of heat in a given resistance as an equal amount of direct current. • Can be determined by the root-mean-square (rms) process. • Also called the rms value. • Erms = 0.707Ep.

  19. Period • The time required to complete one cycle of a sine wave. • Measured in seconds. • The letter t is used to represent period.

  20. Frequency • The number of cycles that occur in a specific period of time. • Expressed in terms of cycles per second. • Unit of frequency is called a hertz. • One hertz equals one cycle per second.

  21. Nonsinusoidal waveforms • Generated by specifically designed electronic circuits. • Represent either current or voltage.

  22. Square waveform

  23. Triangular waveform

  24. Sawtooth waveform

  25. Square waveform • Useful as an electronic signal because its characteristics are easily changed. • Triangular Waveform • Used primarily as electronic signals. • Sawtooth Waveform • Used to sweep the electron beam across the screen, creating an image, as in television sets.

  26. Fundamental frequency • Represents the repetition rate of the waveform. • Harmonics • Higher frequency sine waves that are exact multiples of the fundamental frequency. • Odd harmonics are odd multiples of the fundamental frequency. • Even harmonics are even multiples of the fundamental frequency.

  27. Square waveforms • The fundamental frequency and all odd harmonics. • Triangular waveforms • The fundamental frequency and all odd harmonics, 180 degrees out of phase.

  28. Sawtooth waveforms • Composed of odd and even harmonics, with the even harmonics 180 degrees out of phase with the odd harmonics.

  29. In Summary • AC is the most commonly used type of electricity. • Cycle • Alternations • Hertz • Sinusoidal waveform or sine wave • Peak value of a sine wave

  30. Effective value of AC • Determine effective value by rms process. • The rms value of a sine wave • Period (t) • Frequency (f) • The relationship between frequency and period is: f = 1/t

  31. Nonsinusoidal Waveforms • Square waves • Triangular waveforms • Sawtooth waveforms

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