Phase difference

Chapter Phase difference

Teach Yourself Electricity and Electronics Third Edition Book
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Summary of Contents

Teach Yourself Electricity and Electronics Third Edition Book

  • Phase differenceTwo ac waves might have exactly the same frequency, but they can still have differenteffects because they are “out of sync” with each other. This is especially true when acwaves are added together to produce a third, or composite, signal.If two ac waves have the same frequency and the same magnitude, but differ inphase by 180 degrees (a half cycle), they will cancel each other out, and the net signalwill be zero. If the two waves are in phase, the resulting signal will have the same fre-quency, but twice the amplitude of either signal alone.If two ac waves have the same frequency but different magnitudes, and differ inphase by 180 degrees, the resulting composite signal will have the same frequency asthe originals, and a magnitude equal to the difference between the two. If two suchwaves are exactly in phase, the composite will have the same frequency as the originals,and a magnitude equal to the sum of the two.If the waves have the same frequency but differ in phase by some odd amount suchas 75 degrees or 310 degrees, the resulting signal will have the same frequency, but willnot have the same waveshape as either of the original signals. The variety of such casesis infinite.Household utility current, as you get it from wall outlets, consists of a 60-Hz sinewave with just one phase component. But the energy is transmitted over long distancesin three phases, each differing by 120 degrees or 1/3 cycle. This is what is meant bythree-phase ac. Each of the three ac waves carries 1/3 of the total power in a utilitytransmission line.Amplitude of alternating currentAmplitude is sometimes called magnitude, level, or intensity. Depending on the quan-tity being measured, the magnitude of an ac wave might be given in amperes (for cur-rent), volts (for voltage), or watts (for power).Instantaneous amplitudeThe instantaneous amplitude of an ac wave is the amplitude at some precise momentin time. This constantly changes. The manner in which it varies depends on the wave-form. You have already seen renditions of common ac waveforms in this chapter. In-stantaneous amplitudes are represented by individual points on the wave curves.Peak amplitudeThe peak amplitude of an ac wave is the maximum extent, either positive or negative,that the instantaneous amplitude attains.In many waves, the positive and negative peak amplitudes are the same. But some-times they differ. Figure 9-9 is an example of a wave in which the positive peak ampli-tude is the same as the negative peak amplitude. Figure 9-10 is an illustration of a wavethat has different positive and negative peak amplitudes.Amplitude of alternating current173