1. Not finding help here? Sign up for a free 30min 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!

Equivalent impedance

  1. Nov 23, 2011 #1
    I need help calculating the magnitude of the impedance for a RLC circuit shown below. See the attached schematic.

    I found the impedance magnitude of a similar circuit here:
    Impedance Formulas

    ...see the 4th circuit from the bottom (let's call its impedance Z_a).

    Unfortunately, I do not know how to include the series resistance Rx into this formula.
    The problem I am having is whether to use the formula:
    Z = Rx + Z_a
    ...or
    Z = (Rx^2 + ???)^0.5

    Also, I am not sure whether the value of the Rx will alter the phase angle between current and voltage of this circuit?
     

    Attached Files:

    • ZZZ.png
      ZZZ.png
      File size:
      1.1 KB
      Views:
      55
  2. jcsd
  3. Nov 23, 2011 #2
    First lump R and L into an equivalent series impedance, call it Z1, that will be a complex number: Z1 = R+jwL

    So now you have an impedance Z1 in parallel with C.

    Next, lump the equivalent series impedance found above with the capacitor in parallel into a new equivalent impedance Z2, remembering that the complex impedance of a capacitor is 1/(jwC): Z2 = (Z1 * (1/(jwC)))/(Z1 + 1/(jwc))

    The last lumping is to combine Rx and Z2 as series impedances: Rx + Z2. It will help to get Z2 in terms of a real and complex part (manipulate the thing algebraically) so that you can just add Rx to the real part of Z2.

    Now you can simplify this complex impedance to get a real and a complex term. Now you have the real and imaginary parts of the total circuit, and you use the magnitude formula sqrt(real^2 + img^2) to get the magnitude.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Equivalent impedance
  1. Are these equivalent? (Replies: 5)

  2. Equivalent impedance (Replies: 2)

  3. Equivalent Impedance (Replies: 6)

Loading...