# Resistance Vs Reactance Definition

I am trying to understand the practical distinction between resistance and reactance. As I understand from all what I read the resistance is responsible for the current flow and the reactance is responsible for the rate of change of current (phase shift). Am I right for what I write or my wording isn't right?

Z=R+jX R=Resistance jX=Reactance or it isn't called like this or only "X" term is called reactance and with "j" together is called in different name?

As I understand from all what I read the resistance is responsible for the current flow and the reactance is responsible for the rate of change of current (phase shift). Am I right for what I write or my wording isn't right?

This doesn't make a lot of sense. Current can still flow through a reactive component, and if you apply AC voltage across a resistance, the current through it does have some non-zero rate of change. Maybe just reading through the Wikipedia page for impedance will clear up a lot of things.

A key distinction is that if you apply AC voltage across a resistor, the current waveform will be in phase with (i.e. proportional to) voltage. If you apply AC voltage across a purely reactive element with reactance $$\X\$$, the current waveform will lag (if $$\X > 0\$$) or lead (if $$\X < 0\$$) the voltage waveform. An impedance that isn't purely resistive or reactive will produce a phase shift somewhere in between.

Z=R+jX R=Resistance jX=Reactance or it isn't called like this or only "X" term is called reactance and with "j" together is called in different name?

I believe normally only $$\X\$$ is referred to as reactance, but some sources may differ on that. You could call $$\jX\$$ the reactive component of the impedance.

Both resistance and reactance are forms of impedance, in that they impede the flow of current. However, a major difference between resistance and reactance relates to power and energy. (Power is the rate at which energy is transformed.)

Resistance causes power to be dissipated as heat. A Reactive component does not dissipate power (ideally) but stores potential energy in an electric or magnetic field (or in some cases both). This potential energy can be later "released" back into a circuit.

Z=R+jX R=Resistance jX=Reactance or it isn't called like this or only "X" term is called reactance and with "j" together is called in different name?

I have seen both X and jX referred to as the reactance.

If the reactance is zero then and the phase shift is zero.

Yes. (Slight exception, one can create a circuit without reactance that has a 180 degree phase shift.)

what causes the phase shift.

The terminal voltage across an ideal inductor is proportional to the rate at which the current changes.

$$V = LI'$$

The current through an ideal capacitor is proportional to the rate at which the terminal voltage changes.

$$I = CV'$$

Suppose a current I = sin(wt) is applied to an inductor. Then the voltage across the inductor will be

$$V = LI' = L\text{sin}'(wt) = w L \text{cos}(wt)$$

Suppose a voltage V = sin(wt) is applied to a capacitor. Then the current through the capacitor will be

$$I = CV' = C\text{sin}'(wt) = w C \text{cos}(wt)$$

So the current and voltage for both a capacitor and an inductor are 90 degrees out of phase (although in different directions).

This is the origin of the phase difference the appears when reactive components are excited with sine waves.

• Thanks for your reply. One question. If the reactance is zero then and the phase shift is zero. So the reactance except of didn't dissipate power in heat (ideally) how creates phase shift (I mean with what procedure/mechanism) or phase shift isn't caused from reactance itself? Also, if you please could you tell me your opinion in my second query "Z=R+jX R=Resistance jX=Reactance or it isn't called like this or only "X" term is called reactance and with "j" together is called in different name?"? Commented May 28 at 0:03
• "So the reactance except of didn't dissipate power in heat (ideally) how creates phase shift (I mean with what procedure/mechanism) or phase shift isn't caused from reactance itself?" I'm sorry, but I don't understand this question. Commented May 28 at 0:24
• I mean that the resistance limits the flow of the electrons and the current decreases. I am trying to find a similar exmple of what causes the phase shift. How this phase shift happens from physics side? Thanks again for your reply. Commented May 28 at 0:40
• @DarkKnight If you want the physics then perhaps you should start by understanding resistance and conductance. I don't mean from an electronics standpoint. I mean from a physicist's standpoint, which is very different. If you can collect that idea, then I'd suggest moving on to Feynman's Lecture series, Volume II, perhaps beginning around or near chapter 16/17 on induction and inductors. This is where you begin to gather up the physics side of phase. Also consider reading from Heaviside and Steinmetz. (Or even Maxwell in 1868 On Mr. Grove's "Experiment in Magneto-electric Induction".) Commented May 28 at 6:05