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Steve Nosko wrote:
"Apparently, because of the way the big bang occurred, when we put a voltage across a resistor current flows in a manner that we discovered follows the equation called Ohm`s law." Big bang? Ohm wasn`t around then. He lived 1787 to 1854. Ohm discovered that current in an electrical resistance is proportional to voltage. Resistance is the type of impedance (opposition to electrical current) in which current is locked in step to the applied voltage. The item called a resistor is the type of resistance that converts electrical energy to heat energy. Not all resistances are resistors. Some resistances don`t convert electrical energy directly into heat. In these non-dissipative resistances, current drop is in-phase with the applied volts, or voltage dropped across the resistance is in-phase with current through the resistance, but it does not cause energy loss. An example of lossless resistance is the Zo or surge impedance of a transmission line. Zo is caused by the distributed inductance and capacitance of the line, but current in the line is in-phase with the voltage across the line. Zo is the voltage to current ratio of the waves traveling in either direction on the transmission line. Zo = volts/amps, yet converts no energy to heat in the lossless line. Another example of lossless resistance is "radiation resistance". This is the desired antenna load, so it is hardly a loss. Loss in the wire, earth, and insulators of the antenna are resistive loads which produce heat but don`t help the signal. An ohm is the unit of resistance. It is defined at 0-degrees C, of a uniform column of mercury 106.300 cm long and weighing 14.451 grams. One ohm is the resistance which drops one voltt when a current of one amp is passed through it. Reactances are also defined by their volts to amps ratios (ohms). The big difference is that reactance does no work and produces no heat. Opposition to electrical current comes from delay required to store ard retrieve energy to and from fields in and around the reactances. Current lags the applied voltage in an inductance. At time = 0, no current flows into an inductance, but rises exponentially from the instant of initial energization. Current leads the applied voltage into a capacitance. At time = 0, full current flows into a capacitance but voltage across the capacitance is zero and rises exponentially from the instant of initial energization. In an a-c circuit, the current through an inductance lags the voltage by 90-degrees. In a a-c circuit, the current through a capacitance leads the voltage by 90-degrees. Phase shifts are produced by energy storage in reactance. There is no phase shift in a resistance. No electrical energy is stored in a resistor, but its matter does have a thermal capacity. Once its atoms are agitated by heat their inertia is evident in the resistance`s temperature. It takes time to cool. Steve wrote: "Things get all messed up." As old Carson Robinson sang: "Life gets tedious, Don`t it?" Steve gave the formulas for capacitive and inductive reactances. They have always seemed convenient to me. Steve says: "---we call this new kind of (corrupted) resistance "Impedance"." No. Impedance is the general name for opposition to electricity. Resistance is the specialized name for the case in which the impedance alone causes no delay and stores no electrical energy. All electrical impedance is defined by its voltage to current ratio, and is the total opposition (resistance and reactance) a circuit offers to the flow of electricity. For d-c, reactance doesn`t count. For a-c, total opposition consists of the vector (phasor) sum of resistance and reactance in a circuit. Impedance is measured in ohms and its reciprocal is called admittance. The symbol for impedance is Z. The symbol for admittance is Y. Steve also writes: "Poof! BUT converts it into radio frequency energy (RF) also called an electromagnetic field or wave." Yes. A radio wave is r-f energy which has escaped the confines of wires and doesn`t come back. Whenever wires in open space carry high-frequency current, some energy gets away as a radiated field, having a strength that varies inversely with the distance. Best regards, Richard Harrison, KB5WZI |
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