Reactance does not consume power

Chapter Reactance does not consume power

Teach Yourself Electricity and Electronics Third Edition Book
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Teach Yourself Electricity and Electronics Third Edition Book

  • antenna, you might say you’re “feeding power” through the cable to the antenna. Every-body says this, even engineers and technicians. What’s moving along the cable is imag-inary power, not true power. True power always involves a change in form, such asfrom electrical current and voltage into radio waves.Some true power is dissipated as heat in the transmitter amplifiers and in the feedline (Fig. 17-3). The useful dissipation of true power occurs when the imaginary power,in the form of high-frequency current and voltage, gets to the antenna, where it ischanged into electromagnetic waves.308 Power and resonance in ac circuits17-3True and imaginary power in a radio antenna system.You will often hear expressions such as “forward power” and “reflected power,” or“power is fed from this amplifier to these speakers.” It is all right to talk like this, but itcan sometimes lead to wrong conclusions, especially concerning impedance and stand-ing waves. Then, you need to be keenly aware of the distinction among true, imaginaryand apparent power.Reactance does not consume powerA coil or capacitor cannot dissipate power. The only thing that such a component cando is store energy and then give it back to the circuit a fraction of a cycle later. In reallife, the dielectrics or wires in coils or capacitors dissipate some power as heat, but idealcomponents would not do this.A capacitor, as you have learned, stores energy as an electric field. An inductorstores energy as a magnetic field.