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Resistors connected in parallel and series

  1. Mar 23, 2004 #1
    Hi there,

    I've another problem.... as you can see I'm new to all these... pls forgive!


    point A to B... across A and B there're 2 resistors R(1) and R(2) connected in parallel and R(3) in series to (R(1) and R(2))....

    1) assume R(1)=5ohm, R(3)=2ohm and find R(2) that will make R(AB)=R(3)...

    I thought there's a mistake in the question given that R(AB)= cannot be 2ohm....? correctly me if I', wrong....

    2) assume R(2)=4ohm, R(3)=2ohm and find the value of R(1) that will make R(AB)=R(1)...

    pls advise how do I go about it.

    thanks heaps!!
  2. jcsd
  3. Mar 23, 2004 #2


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    Homework Helper

    Re: resistor

    I agree with your assessment of # 1) based on what's given. For # 2), just use your series parallel stuff. Be careful with your order of combination.

    Step 1: post in the HW forum (for these kinds of q's). It's way the hell down at the bottom, though, so it is understandable that you haven't noticed it.
  4. Mar 23, 2004 #3


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    Science Advisor

    nothing wrong with question #1, and yes, homework section seems appropriate.

  5. Mar 23, 2004 #4
    [tex]R_{AB} = R_1||R_2 + R_3 = \frac{R_1R_2}{R_1 + R_2} + R_3[/tex]
    Both questions require you to solve one equation with one unknown.
  6. Mar 23, 2004 #5


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    Homework Helper

    After reading the two subsequent responses, I would like to change mine for #1). We were probably both thinking too physically, not idealistically enough (that's a hint: what resistance value cannot be obtained for an actual (non-superconducting) resistor?).
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