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Difference Between Resistance and Impedance

resistanceResistance vs Impedance

When you say impedance in electricity, it is often used to described as the measure of the opposition to an alternating current (AC). It is basically resistance but the concept is extended to AC circuits. In AC circuits, amplitudes of both voltage and current, the phases, are shifting and relative. Impedance, in its simplest form, happens with Direct Current (DC); in that case, it is no different from resistance. Resistance is something that “oppose or resist” the flow of current. It prevents the electrons from passing through and usually takes the form of leak energy which is usually heat.

Impedance is much more complicated than resistance, taking into consideration that it relates to AC. Resistance will only have to deal with non-shifting phases of voltage and current which makes it simple. The same thing cannot be said of impedance as it is determined by another value, which is based on phase shifts, aside from resistance. That extra aspect is the reactance.

Reactance, which is either inductive or capacitive, is a circuit element’s opposition to an alternating current. Knowing the reactance in addition to the resistance,one will be able to determine the impedance. This is to say that when one has to determine impedance, they will require an overall or a more extensive figure of the circuit.

Both resistance and impedance are expressed in unit ohms. Mathematically, however, they are denoted differently. Impedance is often denoted with symbol (Z) while resistance is often in (R). Many people, including engineers and electronic enthusiasts use the terms loosely. They often use the terms interchangeably especially in forms where instead of the more appropriate term “resistance”, they will use “impedance”. For instance, simple circuits practically without reactance are still referred with the term “impedance”. Nevertheless, technically speaking, it is still correct. It is always assumed that impedance is just another word for resistance.

Strictly, it should be understood that the effect of resistance is constant regardless of the frequency. On the other hand, mixing the effects of capacitance and inductance will always result in impedance. It basically means that impedance varies frequency values.


1. Impedance is a the measure of opposition to an alternating current (AC) while resistance usually refers to direct current (DC).
2. Resistance is simple while Impedance will consider reactance in addition to resistance to determine it.
3. Resistance is pure ohmic impedance (absence phase shift).
4. Impedance is denoted by (Z) while Resistance is denoted by (R).
5. Impedance may often take into consideration the overall circuit while resistance may not.

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1 Comment

  1. Well written. Many at times people take this two as the same thing. Your article describes the difference clearly for everyone.

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