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!

Finding the parallel impedance in a circuit

  1. Aug 24, 2012 #1
    1. The problem statement, all variables and given/known data
    I need to find the total impedance in a circuit that has:
    j60 ohms, 30 ohms, -j60 ohms and 20 ohms in parallel


    2. Relevant equations
    Ztotal=1/(Z1+ Z2+ Zn)


    3. The attempt at a solution
    I've tried doing this, but what I think is the -j60 and the j60 should cancel therefore leaving only the 30 ohms and 20 ohms in parallel, which would equal 1/50, but the answer says it is 12 ohms.

    Attached is an image of the circuit and answer.
     

    Attached Files:

  2. jcsd
  3. Aug 24, 2012 #2

    gneill

    User Avatar

    Staff: Mentor

    So then, 1/30 + 1/20 = 1/50 ? Check your math.
     
  4. Aug 24, 2012 #3
    Parallel impedance is:

    Ztotal=[1/(Z1+ Z2+ Zn)]^-1

    Also remember when adding fractions you must have a common denominator.

    For example 1/a + 1/b = (a+b)/ab
     
  5. Aug 24, 2012 #4
    but how does that j5 get up there?
     
  6. Aug 24, 2012 #5
    To be honest i think that's a mistake. The negative and positive j components cancel out. That should say 5/20 not j5/j20 even though those two ratios are equivalent.

    If you're having trouble adding fractions try this page:
    http://www.webmath.com/addfract.html
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Finding the parallel impedance in a circuit
Loading...