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Reactance vs. Resistance

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  • Administrator

I am often asked the difference between reactance and resistance. Thought I'd put something here.

Resistance and reactance are both measures of the opposition to the flow of electric current, but they act in different ways and in response to different types of current.

1. Resistance (R): This is a measure of the opposition to the flow of direct current (DC) or alternating current (AC) through a conductor. It arises due to collisions between charge carriers (typically electrons) and the atoms of the conductor. Resistance dissipates energy in the form of heat. The unit of resistance is the ohm (Ω).

2. Reactance (X): This is a measure of the opposition to the flow of AC current caused by capacitance or inductance. Unlike resistance, reactance does not dissipate energy as heat but instead stores it temporarily and returns it to the circuit. It causes a shift in the phase between current and voltage.

   - Capacitive reactance (Xc): This is due to the capacitance in a circuit. It decreases with increasing frequency.
   - Inductive reactance (Xl): This is due to the inductance in a circuit. It increases with increasing frequency.
Reactance and resistance together make up impedance (Z), which is the total opposition to AC current. Impedance is a complex number that takes into account both the magnitude and phase shift caused by the reactance and resistance. The relationship can be expressed as Z = R + jX, where j is the imaginary unit.

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  • Elmer

Reactance is a measure of the opposition to changes in current flow. If the current flow does not change, that is, a steady current, there is no reactive opposition. (Hence, it "reacts" to changes.)


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