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Calculate resistance for this diagram

  1. Jan 20, 2008 #1
    1. The problem statement, all variables and given/known data

    Calculate the equivalent resistance. (Diagram attached)

    2. Relevant equations

    1/Rp=(1/R1)+(1/R2)

    3. The attempt at a solution

    1/25+1/5=1/Rp
    Rp=4.17 ohm

    is it correct?
     

    Attached Files:

  2. jcsd
  3. Jan 20, 2008 #2

    Doc Al

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    Staff: Mentor

    No. Are those resistors in parallel? Hint: What's the significance of the horizontal line in the middle of the diagram?
     
  4. Jan 20, 2008 #3
    No! They are not. There are 2 paths generated, one through both the resistors and the other through only the 5 ohm resistor. So I arrived at the result:
    (1/(5+20))+(1/5)=1/Rp
     
  5. Jan 20, 2008 #4

    Doc Al

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    Staff: Mentor

    Those resistors are not in parallel, but I don't know how you got that new result (which looks like an application of the resistors in parallel formula). Please attempt to answer my other question:

     
  6. Jan 20, 2008 #5
    well, it provides a no resistor path for current. So is the answer 5 ohm?
     
  7. Jan 20, 2008 #6

    Doc Al

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    Staff: Mentor

    Yes! You can treat the wire as being a 0 ohm resistor in parallel with the 20 ohm resistor. Use the formula for parallel resistors to find the equivalent resistance of those two = 0.
     
  8. Jan 20, 2008 #7
    But will you please tell me why wont the current divide at the first branch (as my teacher told me)?
     
  9. Jan 20, 2008 #8

    Doc Al

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    Staff: Mentor

    Since one of those branches has zero resistance, all of the current "chooses" that branch.
     
  10. Jan 20, 2008 #9
    Thanx!!!!!!!!!!
     
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