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Series/Parallel Circuit Help

  1. Jan 11, 2009 #1
    Wats up fellow forumers. I just signed up for physics forum, looks like an awsome forum that I will be as active as I can in. In class I got these circuit questions for review and I just don't know if I know how to figure them out. They are series/parallel brightness questions. It says to order them from brightest to least bright, ex. (A=B>C>D=E). I know that parallel are less resistence than series.

    1. The problem statement, all variables and given/known data
    Here is a link to the circuits re-drawn in Paint

    2. Relevant equations
    Parallel Resistance < Series Resistance

    3. The attempt at a solution
    Here is what I think they are ( but I guess I am wrong at pretty much all of them)
    5.E=B>C=D>A (I didn't really know how to do this one at all, pure guess)

    If you could just tell me which ones are wrong and right. And with the ones that are wrong, could you please give me an explanation of why mine is wrong and yours is right. The explanation doesn't have to be long, just get the point over.

    Any questions, comments, suggestions just post. I will be looking over this very often as I need this info with-in a few days ^^.

  2. jcsd
  3. Jan 13, 2009 #2
    Welcome to physicsforums! Let's start with the first circuit, shall we?
    Assuming all bulbs have the same resistance, then...

    Should be C>A=B=>D=E

    You got the fact that C > D=E correct, but consider this. The overall circuit has one total current. When it meets the first branch AB, it splits into 2 equal currents, and meets up again at the end of the branch. When the current hits the following branch, it splits into 2 currents again, but more so across the C bulb. Current is lazy and prefers the path of least resistance, and bulb C has less resistance than D+E. So more current goes through the bulb C, more than half of the total current, which makes the bulb brighter than A and B.

    Are you comfortable with that explanation? I wanna make sure you get that before I move on to the other parts.
  4. Jan 13, 2009 #3
    Yeh I get that, could someone please check the rest, it's due tomarrow. >.<
    And yes they are all the same resistance
    Last edited: Jan 13, 2009
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