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Homework Help: Resistors in parallel and series

  1. Apr 20, 2013 #1
    1. The problem statement, all variables and given/known data

    If an ohmmeter is connected between points and in each of the circuits shown in the figure . For the circuit a) what will it read? For the circuit b) what will it read?


    2. Relevant equations

    Series and Parallel rules

    3. The attempt at a solution

    I need help just in part b. Now, when we combine the 30 and 45 resistors, the solution manual combines them in parallel and the equivillant is drawn on the bottom line. My question is WHERE DID THE WIRE IN THE MIDDLE GO? Did it miraculously dissapear?... I need tips in knowing how to determine parallel in series.. ??? Thanks for any help
  2. jcsd
  3. Apr 20, 2013 #2

    Doc Al

    User Avatar

    Staff: Mentor

    What middle wire? Unless the wires (and the connections) are labeled, we'll have a difficult time discussing them.

    In any case, if you can pick two points and redraw the wires such that the 30 and 45 resistors are in parallel between them (and you can), then you are justified in replacing them with the equivalent.
  4. Apr 20, 2013 #3
    I mean here the wire at which the 30 ohm resistor is placed. When drawn equivilantly with the 45 ohm resistor, they put them on the very bottom line and take off the wire which the 30 ohm resistor was originally placed at!
  5. Apr 20, 2013 #4

    Doc Al

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    Staff: Mentor

    Still not clear where the problem is.

    In your diagram, look at the rectangle that contains the two resistors. Label the corners a, b, c, d, starting with the upper left and going clockwise. Would you not agree that a,b, and c are essentially the same point? And thus between that point and point d, the two resistors are in parallel.
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