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Homework Help: Finding the current through each of the resistors

  1. Sep 7, 2011 #1
    1. The problem statement, all variables and given/known data
    I need help with this problem. I would appreciate it if you could explain how you got your answer.

    In the diagram below, what are the currents in each of the resistors? Show how you arrived at your answer.

    [PLAIN]http://img801.imageshack.us/img801/6237/unledoer.png [Broken]

    2. Relevant equations

    V=IR? I'm not sure if this is a parallel circuit. I'm guessing if it were Is = Vs/R1 +Vs/R2 + Vs/R3

    3. The attempt at a solution

    I really don't know where to start.
    Last edited by a moderator: May 5, 2017
  2. jcsd
  3. Sep 7, 2011 #2


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    Staff: Mentor

    If current is able to flow (remember, it goes from the +ve terminal of the battery to the battery's -ve terminal) through any resistor without going through any other element, then that resistor is in a parallel circuit. Trace out the complete path current must take through R10. Does any of the current through R10 pass through any other resistor to reach the -ve terminal of the battery?

    Another way of looking at it: could you remove from the circuit some resistors (i.e., use an eraser to erase them from your pencil drawing) without affecting the current through R10? If so, then R10 must be in its own parallel circuit.
    Last edited: Sep 7, 2011
  4. Sep 7, 2011 #3
    Thanks!!! I got it.
  5. Sep 8, 2011 #4


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    Staff: Mentor

    A different approach would be to take a red marking pen, and from the + terminal of the battery colour the wires red right up to each element. Every point on that red line is at the same voltage as the + terminal of the battery. Similarly, use a blue pen for wires from the - terminal.

    You can then see how every resistor has one of its ends sitting at the battery's + voltage, and the other end at the - voltage. So, having shown that the battery voltage is being applied directly across each resistor, you can calculate their individual currents.
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