Finding unknowns in a Series/Parallel Circuit

Discussion in 'Homework Help' started by MrGR, Jan 27, 2008.

  1. MrGR

    Thread Starter New Member

    Jan 26, 2008
    We have studied series and parallel circuits in our class. We have been given an extra credit problem that consists of a series-parallel circuit that we are to find the unknowns. I have attached a copy of the problem. I am not looking for answers, just some guidance as to how I can attack it. Any help is greatly appreciated
  2. thingmaker3

    Retired Moderator

    May 16, 2005
    The first thing I would do is to re-draw the circuit. I would try draw it in a way to make obvious which resistors tie to battery + and - and are therefore in parallel.

    I would then solve any series resistances as equivalent resistance. Next I'd do the same for the parallel resistances.
  3. MrGR

    Thread Starter New Member

    Jan 26, 2008
    Thank you for your suggestion, thingmaker3. I'm not sure why, but I am really struggling with getting this simplified. It's embarrasing because I know that this isn't a real complex circuit. I know how to use Ohm's Law, KCV, and KCL. If someone could help me with simplifying the circuit I would appreciate it.
  4. S_lannan

    Active Member

    Jun 20, 2007
    when tackling something like this i look for groups of known things that can help find an unknown thing.

    eg - we know the value of r1 and r2.
    we know that kvl states that Vsupply = vr1 + vr2

    so if we simplify that series loop by adding r1+r2 we can find the current going
    through that branch by using ohms law

    I = Vsupply / (r1+r2). ----> I = 10/1100 ------> I=9.09mA

    now that we know the current going through those two resistors we can
    figure out how much voltage drops across them.

    Hope that demo helps...
  5. MrGR

    Thread Starter New Member

    Jan 26, 2008
    I have worked through this problem the best that I know how. I would greatly appreciate it if someone would look over my worksheet and check my logic. I would like to thank everyone in advance for their help and encouragement.
  6. JoeJester

    AAC Fanatic!

    Apr 26, 2005

    You did make some errors.

    Attached is my calculations.