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Minimum output e.m.f. of the power source

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

    2. Relevant equations
    V=IR
    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

    jbriggs444

    User Avatar
    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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