Re: is resistance equal to reactance?

Resistance and Reactance are similar, in that they have the same 
units (ohms) and control the flow of charge, but not exactly alike. 
Resistance is found in nearly all materials and in both AC and DC 
circuits. Reactance is a property of specific components and devices, 
is only seen in AC circuits and depends on their physical 
construction.

The resistance of conducting materials is influenced by the length, 
cross-sectional area and the temperature. It is often compared to a 
friction force that resists charge moving. The resistance, R, in a DC 
circuit can be calculated by Ohm’s Law, R=V/I. This also holds true in 
an AC circuit where there is little or no inductance or capacitance. In 
such a case the current and the voltage would be in phase. That is to 
say the peak voltage and the peak current will occur at the same time 
and they will also go to zero at the same time. In fact, if it can be 
shown that this is not true, this is evidence that there is some 
capacitance and/or inductance in the circuit.

Inductance occurs when there is a coiling of the wire to produce a 
magnetic field. The changing current creates variations in the 
magnetic field. These variations induce a reverse electric potential in 
that same coil and act to limit the current (sort of like resistance 
would do). This effect is called reactance, XL. The X stands for the 
Reactance and the L identifies the coil as an inductor, L. It is of 
interest that this effect is not in phase with the applied voltage but 
leads it by 90° or ¼ cycle. Low frequencies have less effect and 
reduce reactance … high frequencies create lots of reactance in the 
same device.

Capacitance occurs when the conducting path is interrupted by an 
insulating gap. In a DC circuit, this would prevent any current and 
would look like an infinite resistance. However, since AC currents 
don’t continue forever, there may still be some limited temporary 
movement. Capacitors are constructed with large surface areas to 
confine a small but measurable amount of charge to accumulate 
without passing through to the other side. As the AC voltage reverses 
polarity, the process reverses. Therefore, charge can go back and 
forth in the wires, and into and out of the capacitor with some limited 
effect. Hence, the capacitor allows an AC current but with some limits 
(sort of like resistance). Again the current does not peak at the same 
time as the pushing voltage but lags 90° behind or ¼ cycle. Low 
frequencies have more effect and increase reactance … high 
frequencies create little reactance in the same device.

More information, diagrams, and examples can be found at the 
following web sites:
www.electronics-tutorials.com/basics/reactance.htm
www.ibiblio.org/obp/electricCircuits/AC/AC_4.html
www.ibiblio.org/obp/electricCircuits/AC/AC_5.html

For more information, Go to Google and enter either reactance or 
impedance.