1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Problem with Impedance

  1. Oct 22, 2008 #1
    1. The problem statement, all variables and given/known data

    A particular inductor has appreciable resis-
    tance. When the inductor is connected to a
    19.7 V battery, the current in the inductor is
    4.38 A. When it is connected to AC source
    with an rms output of 19.7 V and a frequency
    of 58 Hz, the current drops to 1.65 A.
    Find the impedance at 58 Hz.
    Answer in units of

    2. Relevant equations

    Z=sqrt(R^2 +(XL-XC)^2)



    3. The attempt at a solution

    XL=19.7 V / 4.38 A = 4.49772 ohms

    R = 19.7 V / 1.65 A = 11.9394 ohms

    Z= sqrt( 11.9394^2 + 4.49772^2) = 12.7585 ohms
  2. jcsd
  3. Oct 22, 2008 #2
    Re: impedance

    I am afraid you mixed them up.
    The higher current is when you have only resistance. (I1=V/R)
    The lower current is I2 = V/Z and not V/XL.
  4. Oct 22, 2008 #3
    Re: impedance

    Ok I understand my mistake now. Thank you for clearing that up for me!
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook