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Voltage drop across connecting wires?

  1. Oct 24, 2016 #1
    1. The problem statement, all variables and given/known data
    Suppose you want to run some apparatus that is 95 m from an electric outlet. Each of the wires connecting your apparatus to the 120 V source has a resistance per unit length of 0.0065 Ω/m. If your apparatus draws 2.9 A, what will be the voltage drop across the connecting wires and what voltage will be applied to your apparatus?

    2. Relevant equations
    V=IR

    3. The attempt at a solution
    For voltage drop:
    Rwire=.0065(95)=.6175Ω
    V=IR=2.9*.6175=1.79*2(to apparatus and back)=3.58V which was wrong.

    I got the answer to what voltage will be applied to your apparatus which was:
    Rapparatus=V/I=120/2.9=411.379Ω
    Rtotal=Rapp+Rwire=41.379+.6175=41.996Ω
    Itot=V/Rtot=12-/42=2.85A
    V=ItotRwire=2.85*.6175=1.764V
    120V-1.764V=118.23V
     
  2. jcsd
  3. Oct 24, 2016 #2

    SammyS

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    They may be looking for the voltage drop across each wire individually.
     
  4. Oct 24, 2016 #3
    Yup, you're right. It's V=(2.9)(.6175)=1.79V
     
  5. Oct 25, 2016 #4

    gneill

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    Staff: Mentor

    The problem statement is ambiguous about whether the 2.9 A for the apparatus is meant to be its rated current at 120 V, or if it's the actual current drawn when in operation at the end of the 95 m cable. The latter seems to be the case if the voltage drop on the cables is correctly calculated using that current value. Knowing the source voltage and the cable voltage drop, KVL will tell you what's left for the load...
     
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