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Homework Help: Voltage Drop Calculation

  1. Sep 15, 2010 #1
    1. The problem statement, all variables and given/known data
    Suppose you want to run some apparatus that is 75m from an electric outlet. Each of the wires connecting your apparatus to the 100V source has a resistance per unit length of 0.0055 ohms/m. If your apparatus draws 2.5 Amps, 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

    100=R x 2.5
    So R= 40 Ohms

    But don't know where to go from here!
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Sep 15, 2010 #2

    Delphi51

    User Avatar
    Homework Helper

    Careful with that formula! It must be applied consistently to one component. The 100 Volts appears across the combination of the wire and the apparatus. (You can treat the combination as one component "in a black box" and use 100 = R*2.5 to find the combined resistance of the wire and the apparatus. But that doesn't do you much good.)

    Better to begin by figuring out the resistance of the wire from the other information given (resistance per m of length). Then apply the formula to the wire only and find the voltage across the wire only, answering the first question.
     
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