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Homework Help: Finding Current in a Circuit with 3 Switches

  1. Mar 25, 2010 #1
    1. The problem statement, all variables and given/known data

    A circuit containing three switches, labeled S1, S2, and S3.
    Find the current at a for all possible combinations of switch settings.
    Put = 170 V, R1 = 30.0 , and R2 = 10.0 .
    Assume that the battery has no resistance.

    (S1, S2, and S3 all open)
    (S1 closed, S2 and S3 open)
    (S2 closed, S1 and S3 open)
    (S3 closed, S1 and S2 open)
    (S1 open, S2 and S3 closed)
    (S2 open, S1 and S3 closed)
    (S3 open, S1 and S2 closed)
    (S1, S2, and S3 all closed)

    Figure Shown here: http://www.webassign.net/hrw/28_37.gif" [Broken]
    2. Relevant equations


    3. The attempt at a solution
    I'm confused on what it means when a circuit is open or closed, so I don't know how that affects the current.

    Also, I don't know how to account for the 2 resistances.

    Please help! :)
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Mar 25, 2010 #2
    The switches are open or closed. You just have to draw 8 versions of the circuit, with the closed switches replaced by a wire, and the open switches, and everything that's in series with them removed from the circuit.

    You could draw a tree with the original cicuit at the root, and then 2 circuits as branches, one of them with S3 closed and one of them with S3 open. Simplify those circuits by replacing series and parallel resistances. Then split both branches in a branch with S2 closed and s2 open. replace series and parallel resistances again, etc.
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