Rlc Circuit Question

Discussion in 'Homework Help' started by Mr Walker, Jul 10, 2008.

  1. Mr Walker

    Thread Starter New Member

    Aug 15, 2007
    When finding impedance Z. When should this equation be used.



  2. JuniorEE

    New Member

    Feb 26, 2008
    Well, I'm pretty sure the first part is just the conversion from regular resistance, capacitance, and inductance to the real +/- imaginary impedance. This link will help you understand it more:


    You'd want to use those equations when you're finding the Total Impedance in a circuit.

    The second equation I'm not entirely sure about. Where did you get the pictures from?
  3. silvrstring

    Active Member

    Mar 27, 2008
    At school, I always use the first two forms for impedence--rectangular form and polar form. There is no need for the subscripts, though; the values of the real and complex numbers, or the impedence and the phase angle, describe whether the circuit or component is inductive or capacitive.

    For the last part, I will include (cap.), or (ind.), after the ohmic reactance value if I am labeling the reactance of a circuit or component(s). The Z calculations you have still require the phase angle, though. We always include that when doing homework or taking tests.
  4. Mr Walker

    Thread Starter New Member

    Aug 15, 2007
    I originally thought you would find total impedance by doing the rectangular to polar conversion equation. But then I was taking a test for a job, and when I did the the the rectangular to polar equation the answer didn't match.

    I got the first picture from allaboutcircuits.


    and the second from

    http://www.tpub.com/neets/book2/4l.htm just something I found on the net.
  5. theamber

    AAC Fanatic!

    Jun 13, 2008
    The bottom formula es called the Phytagorean theorem and is used in conjunction with trigonometry to get the results in the upper part of your post. Conversion from Rectangular to Polar form.
    The phythatgorean theorem will get you the magnitud in polar form and the arctan in trigonometry will give you the angle. Then you can have rectangular numbers in polar form them you can do regular arithmetic with this polar numbers and calculate E,I,R,Z. as you will do in an DC circuit. A calculator with the ability to change rectangular to polar form will be usefull like the Texas Instruments TI89.
    So in polar form you get a number(magnitud) and and angle(direction).
    You need to study complex numbers and vectors to understand this.
    When calculatin AC circuits you need to use complex numbers form because of the phase diferences present in AC circuits.
    You must express a quantity in magnitud and angle when analyzing AC circuits.