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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    1,796
    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

    Google and Wiki are your friends -- use them!
    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

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