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Homework Help: Urgent test In 58 Minutes

  1. Feb 14, 2008 #1
    Urgent...test In 58 Minutes!!!!

    1. The problem statement, all variables and given/known data

    I am having a hard time figuring out how to calculate the current in a circuit consisting of 2 batteries and numerous resistors. Unfortunautely the problem I am trying to do is in my book so I can't post a picture. But if someone can give me a general idea of how to approach these kinds of problems I would greatly appreaciate it!

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Feb 14, 2008 #2


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    Homework Helper

    Replace blocks of resistors in paralle with a single equivalent resistor.
    Remember that voltage drops accross each resistor in a circuit must add up to the battery voltage.
    current through all resistors in series must bee the same.
  4. Feb 14, 2008 #3
    have you learnt kirchoff's laws before? learning your concepts right before your exam is not good.
  5. Feb 14, 2008 #4


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    It's kind of difficult to help you if you haven't posted a specific problem. But you only need to use Kirchoff's voltage law and Kirchoff's current law here. Remember that the potential difference across a resistor is simply V = IR. Start by labeling currents in the circuit as I1, I2, I3 etc.

    Well, that's all I can say without any more input from you.

    EDIT: To mgb_phys advice I would add that you should always replace resistors in series with equivalent resistors. Kinda obvious I know.

    This is a little off-track but it seems like you're panicking over something which you probably know how to do outside of exams. Have a look through your tutorials to refresh your memory.
    Last edited: Feb 14, 2008
  6. Feb 14, 2008 #5
    I redrew the picture with 2 batteries 1 on each side and 2 resistors 1 on top and 1 bottom. Now that I calculated the current through the top resistor how do I work backwards to calculate the current through the each individual resistors that make up that equivalent resistor? Does that make sense?
  7. Feb 14, 2008 #6
    I ended up with having a 12 V bat on the left side of the circuit then a 24 Ohm Resistor on the top, a 3 V bat on the right and a 3 Ohm Resistor on the bottom. Also how do I know which bat to use to calculate the current?
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