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: Resistor network

  1. Jan 28, 2006 #1
    Can someone tell me where I'm going wrong here?
    I'm uploading a jpeg of the circuit, I'm supposed to find the equivalent resistance between A and B.

    To me, it looks like R5 and R6 are in parallel and forming Rp56. From there I'm assuming that Rp56 would be in parallel with R3 and then that whole top part (R5, R6, and R3) would be in series with R4.

    Can someone point out where I'm making my error? I'm coming up with a total resistance of 5k and the answer should be 4k.

    Attached Files:

  2. jcsd
  3. Jan 28, 2006 #2
    This is incorrect because the chain is more complex due to the different interconnecting wires. What you need to do is to apply Kirchoff's Law. Do you know this procedure ? You basically apply charge conservation and energy conservation on each subchain. So, the first thing to do is to detect each subchain (you have three such chaines in your case).

  4. Jan 28, 2006 #3
    To be in parallel, the two resistors have to have the same potentials at BOTH ends, which means both their ends touch each other. Here 5 and 6 only touch at one end. Shorten all the wires and redraw the circuit without wires and see which resistors touch at both ends. I did it and came up with 4k as the answer.
  5. Jan 29, 2006 #4
    I think I have it, at least I'm coming up with the correct answer now.

    Going back to the original diagram, R4 and R3 are in parallel giving a resistance of 2k which is in series with R5. This equivalent resistance is then in parallel with R6.

    Sound right? Thanks for the help guys.

    Oh, and thanks for not just spewing out the answer, it makes a lot more sense now.

  6. Jan 29, 2006 #5
    That's the way I got it.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook