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Homework Help: Find and calculate current in a circuit

  1. Mar 3, 2010 #1
    1. The problem statement, all variables and given/known data
    Consider the following configuration.
    2yy341e.gif
    Given:
    EMF1=6 V
    EMF2 = 3 V
    R1 = 600 Ohm
    R3 = 100 Ohm

    1. Calculate the current i1.
    2. Calculate the current i3.


    2. Relevant equations
    V=IR
    Kirchoff's circuit laws:
    1. Sum of current into any node is zero.
    2. Sum of voltages around any loop is zero.


    3. The attempt at a solution
    I know that the potential at point A is 6 V because of the battery. I can't figure out how to calculate i1. I think I somehow have to use Kirchoff's rule, but I just don't know how. I tried to set up a voltage equation: EMF1 -i1R1 - i3R3 = 0. I don't know if that's right but it still has two unknowns. For i3, it seems like I have to know what i1 is to calculate it. Any help is appreciated!
     
  2. jcsd
  3. Mar 3, 2010 #2

    rl.bhat

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    Homework Helper

    This voltage equation: EMF1 -i1R1 - i3R3 = 0. is correct.
    Write down similar equation for EMF2. Put i3 = i1 + i2 and solve the equations to find i1 and i2.
     
  4. Mar 3, 2010 #3
    How would I know which resistor i2 corresponds to?
     
  5. Mar 3, 2010 #4

    rl.bhat

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    Homework Helper

    EMF2 - (i1 + i2)R3 = 0.
     
  6. Mar 3, 2010 #5
    Ah, that makes sense. So I set those two voltage equations equal to each other and solved for i1. Then I plugged i1 into the EMF2 voltage equation and solved for i2. I finally added i1 and i2 together to get i3. Thanks so much!
     
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