# why new word reactance

Discussion in 'General Electronics Chat' started by raks_universe, May 3, 2009.

1. ### raks_universe Thread Starter Active Member

Mar 15, 2009
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Inductors "oppose" the applied current flow(Lenz law),then why we are not calling it as a resistance of inductor,and instead why we use a new word "reactance" for denoting it . Is reactance and resistance are same.(please notify the difference)

2. ### Papabravo Expert

Feb 24, 2006
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2,557
Resitance occurs in both DC and AC circuits. Reactance only occurs in AC circuits. It happens when voltage or current is a function of the time rate of change of the other.
Code ( (Unknown Language)):
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2. v = L * (di/dt)
3. i = C *(dv/dt)
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Reactance is always a function of frequency, resistance is not a function of frequency

http://en.wikipedia.org/wiki/Electrical_reactance

3. ### KL7AJ AAC Fanatic!

Nov 4, 2008
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Energy will be LOST in a resistance, but not in a reactance.

I might add that there ARE frequency dependent resistances, such as skin effect, but they are minor except at high radio frequencies.

Eric

4. ### mbohuntr Senior Member

Apr 6, 2009
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I agree, A resistor value is constant through a great range of frequencies, while an inductor as well as a capacitors reactance(resistance) will vary with frequency making them useful in filters for music and commication. The value must be calculated separately before being considered with resistance.

5. ### t_n_k AAC Fanatic!

Mar 6, 2009
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KL&AJ makes an important distinction.

Inductors and capacitors are able to store energy (in magnetic and electrostatic fields respectively) while resistors cannot store energy - they only dissipate energy as heat.

6. ### t_n_k AAC Fanatic!

Mar 6, 2009
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Apologies KL7AJ for the unintended name change!

7. ### Papabravo Expert

Feb 24, 2006
11,928
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Quite right and, at sufficiently high frequencies an inductor develops inter-winding capacitance and starts to look like a capacitor, while capacitors start to look like inductors. Plotting a Smith Chart on a network analyzer for an apparently "simple" component is a truly mind bending experience as the complex impedance loops around and around.

But that is way beyond the original question

8. ### raks_universe Thread Starter Active Member

Mar 15, 2009
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0
Did you mean the reactance as only a phase change against current?
If so,did they cause any power dissipation(pure) or not?