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Homework Help: Minimum output e.m.f. of the power source

  1. Sep 30, 2015 #1
    1. The problem statement, all variables and given/known data

    2. Relevant equations
    For resistors connected in parallel, 1/R =1/R1 + 1/R2 +...

    3. The attempt at a solution
    I first calculated the resistance of the the cable which consists of two wires,
    1/R= 1/0.0050 + 1/0.0050
    R = 2.5x10^-3 x 800
    = 2 Ω
    Then I calculate the voltage across the cable, V=0.060x2= 0.12V
    So the total p.d would be 0.12V+16.0V=16.12V, and I chose A, but the correct answer is C. Why?
    Please help, thanks
  2. jcsd
  3. Sep 30, 2015 #2


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    Science Advisor

    One of the wires in the cable carries current toward the relay and one carries the current back toward the power supply, right? If you drew that as a circuit diagram, would that makes those wires parallel or series?
  4. Sep 30, 2015 #3
    Oh right! It's series. I misread the question. I've figured out the answer already. Thank you!
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