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Capacitor and inductor reactance

Discussion in 'Electronics Homework Help' started by Zeeman2000, Mar 2, 2015.

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  1. Zeeman2000


    Mar 2, 2015
    Hello everyone,

    I am currently working through a self study book on electronics. I have starting a chapter which is an introduction to Alternating Current. The chapter discusses capacitor and inductor reactance using the following formulas:

    XL = 2pifL
    XC = 1/2pifC

    At the end of the chapter there is a self test which gives a value of a capacitor reactance and the value of a capacitor or inductor and asks to find the frequecy necessary to cause reactance.

    The equation for this was not dicussed im the chapter. Can someone explain the equation needed to find the answer?

    I tried the equation in reverse which worked for:


    6.28 * 100 * 10 = 6280 ohms

    6280 / 10 / 6.28 = 100Hz

    In the self test the values are:

    L = 50 μH, XL = 320 ohms, f =

    320 / 50 / 6.28 = 1.019108280254777

    Book answer was 1.02kHz

    Not sure how they are getting this answer. Any help much appreciatted.
  2. Laplace


    Apr 4, 2010
    Units in the formula are Ohm, Hertz, and Henry. 50 μH = 0.000050 H.
  3. Zeeman2000


    Mar 2, 2015
    Yes, 50 μH = 0.000050 H

    Turns out the question in the book was wrong. I have since checked the errata and it should have read 50mH not 50μH

    As even using 0.000050 H gave and answer in MHz
  4. BobK


    Jan 5, 2010
    Yep, at 50mH the answer in the book is right.

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