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Homework Help: Equivalent impedance

  1. Dec 9, 2007 #1
    hello I have a problem in calculating the equivalent impedance of a simple AC circuit, where the impedances are:

    Z1 = 5+i20
    Z2 = 5+i20
    Z3 = 10-i2,5
    Z4 = -i10
    Z5 = 5

    and I need to find:

    Z_eq = Z3 // [(Z1 // Z4) + (Z2 // Z5)]

    where the + indicates 2 components in serie and the // indicates 2 components in parallel.

    My calculations always bring me to

    but my book says Z_eq=28,33.

    Which is the correct eqv impedance?

    Thank you
    PS-I used the formula Za//Zb = (Za*Zb)/(Za+Zb)
    to calculate equivalent impedances of two components in parallel, and the sum for components in serie.
  2. jcsd
  3. Dec 10, 2007 #2

    The Electrician

    User Avatar
    Gold Member

    Well, there's a mistake somewhere.

    If I use the values you gave for Z1 to Z5, I get the same result you did.

    However, if you set Z3 = 5 + i20, then you will get the result in the book.
  4. Dec 10, 2007 #3
    Ok then there probably is a mistake in the book because Z3 is in fact equal to 10-i2,5 as I calculated and as the book reports. Lost some time on this stupid mistake...

    Thank you very much for taking the time to verify this! :)

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