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Current Divider Rule

  1. Jul 29, 2007 #1
    Hello everyone.
    im amit, newbie in this forums, hopefully im posting my question in the correct one.
    anyways, i was trying to solve this qustion from last semester considering the attached image as a circut
    with voltage source of 30V

    the task was to find the current over the resistor position diagonally R=20 Ohm

    My assumption was with a total equivalent current of 2A is flowing over the 5 Ohm resistor , then to be divided between 10/20 Ohm resistors and then again between 10/20 ... what gives to result of 2/3A which is .... wrong.

    result is 0.5A , but why ??? does it matter in which direction i concider the current flow ? how can I know which is the right direction if so ?

    thanks alot, exam coming by the end of the week
    cya around. amit.

    Attached Files:

  2. jcsd
  3. Jul 29, 2007 #2
    You are correct with that 2A flows from the source through the 5 Ohm resistor. Now look at the equivalent resistance on both branches. Both paths have a 20 Ohm resistance (20 Ohm on left and 20||20 + 10 = 20 Ohm). So the current is divided equally to 1A each. So now that 1A flows through the 10 Ohm resistor and gets to the point where the diagonal 20 Ohm connects with the vertical 20 Ohm. Both paths have equal resistance so the current evenly splits again to 0.5A each.

    The direction does not matter. In general when you solve for current and get a minus sign that just means your initial guess at the direction was wrong. The current flows the opposite way instead.
  4. Jul 29, 2007 #3
    Allllright .. i think i got it now

    from what i got from your answer one should always consider the total resistance when one calculate those sorts of problem, i tried to guess it each time with a specific resistor with a specific resistance and didnt consider other resistors might be connected and influencive.

    now i know


    Amit, Germany.
  5. Jul 31, 2007 #4
    Hope it helps. This stuff becomes easier as you get more experience doing these types of problems.
  6. Jul 31, 2007 #5
    Thanks man, hopefully i can just forget about it after this friday, if ill pass the exam i failed last semester togather with this semester's course exam (Electical Engineering 1+2)

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