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Inductive and capacitive reactance

  1. May 3, 2017 #1
    Why is it that capacitive reactance is subtracted from inductive reactance and not the other way around when determining the overall reactance?
  2. jcsd
  3. May 3, 2017 #2
    What is the formula for capacitive reactance?

    With a j in the denominator, the term becomes negative when you bring it to the numerator.

  4. May 4, 2017 #3


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    Staff: Mentor

    Reactances in series add. Inductive reactance has a + associated with it, and capacitive reactance has a – associated with it. They keep these signs when you add them, and the result can end up being a net + or a net – depending on the magnitudes.
  5. May 4, 2017 #4

    jim hardy

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    Science Advisor
    Gold Member

    Have you been yet introduced to phasor notation?

    The answer to your question is "By Convention"
    and it's related to the physical facts that
    current leads voltage in capacitors
    current lags voltage in inductors .

    So a long long time ago the heavy thinkers {Steinmetz i think it was and Tesla picked right up on it)
    decided that capacitance would get the minus sign and inductance the positive sign . Consistency kept their algebra simple. We never changed.

    Be rigorous in your arithmetic and form good math habits. It'll pay off.

    old jim
    Last edited: May 4, 2017
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