homework help

Discussion in 'Homework Help' started by NeoKu, Mar 11, 2013.

  1. NeoKu

    Thread Starter New Member

    Mar 11, 2013
    1
    0
    i am confused on what to do on the rest. can someone please help
     
  2. panic mode

    Senior Member

    Oct 10, 2011
    1,318
    304
    well, i would start from scratch.

    first your image is mirrored (easily fixed) then it is not exactly readable (bigger problem).

    your equivalent circuit is not correct and therefore it's no surprise that results don't match either.

    i suggest to start by marking all nodes of the circuit and then make equivalent (though "rectangular") representation.

    hint: top side of the battery (thin long line) is a positive terminal. how many resistors are connected to it in original circuit? does that match your circuit?

    hint2: do the same for the negative side of the battery, how many resistors are connected to it in each of the circuits? your equivalent circuit shows that negative side connects to R3 but it should also connect to R2.

    hint3: when computing equivalent circuit parameters (such as resistance) try to break it down. you made a mistake in calculation by trying to combine three resistors into Ra.

    if a node has only two components connected to it (and the other side of those components are in different nodes), then those two components are in series.

    when drawing equivalent circuit, it is a good idea to mark nodes in a same way as in original circuit. then you can verify your creation by comparing what is between any two nodes. they must be the same.

    next step is to mark all currents. for example you can use same index (current through R1 is I1, current through R2 is I2, current through R3 is I3 etc.).

    if computing equivalent resistance of portions of the circuit, it is important to make sure that order is correct. you need to choose name for new component that is simplification (equivalent) of two or more components. for example if there was series circuit of R7 and R8
    we could write

    R78 = R7 + R8

    suppose this was in parallel with R5
    R578=R5 || R78

    or you can use node names (Rab, Rac, etc.)
    whatever you choose is up to you but this small-step approach is what i meant in hint3 (until you gain experience, stick to combining two resistors into one, don't go to three resistors in one step).
     
  3. WBahn

    Moderator

    Mar 31, 2012
    17,715
    4,788
    When you go to post a scan or a pic, be sure to look at it yourself and try to put yourself in the place of the stranger that has to get all of their information from the picture plus whatever you put in your post.

    Despite the mirroring, I have a very hard time figuring out what you have written in the margin (left margin in the picture as posted). You want to make your work as easy as possible for someone to follow, whether it's us or the grader.
     
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