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Homework Help: Circuits: Direction of Current

  1. Apr 19, 2010 #1
    1. The problem statement, all variables and given/known data

    The question gives me a diagram and is asking me to find the direction of the current through a resistor. I understand that current always flows from positive to negative terminal of the power source but the thing is, I'm given 3 batteries and a resistor (which I don't know how to figure out). The diagram goes like this (I'll have to describe in words):

    Picture a square circuit; I will describe clockwise starting from bottom of the square. On the bottom of the circuit, there is a battery of 4V with the positive end on the left side of the page and negative on the right side. On the left side of the square, there is another battery of 2V with negative on the bottom and positive on the top. There is a resistor on the top of the square. On the right side of the square, there is a battery of 9V with positive end on top and negative end on bottom.

    2. Relevant equations


    3. The attempt at a solution

    Apparently, the current through the resistor is from right to left. I don't understand how I would figure it out because we have positive to positive ends of the resistor!
  2. jcsd
  3. Apr 19, 2010 #2
    When you have voltage sources (like batteries) in series you figure out the voltage by starting at one end and going though all the batteries and adding it all up. If you go from a negative terminal to a positive terminal through a battery you add the voltage. If you go through a battery from positive to negative then you subtract the battery's voltage.

    If you connect the + terminals of a 10 volt and 11 volt battery together then between the free - terminals you will measure 1 volt.
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