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Negative sign in voltage equation

  1. Apr 2, 2014 #1
    hello
    as we know if we wanta find the resistance of a material we use this equation
    %7D.%5Cvec%7Bdl%7D%29%7D%7B%5Cint%20%5Cint%20%28%5Csigma%5Cvec%7BE%7D.%5Cvec%7Bds%7D%29%20%29%7D.gif
    but in electromagnetic course we know that voltage equation has negative sign that it is refer to positive charge thas positive sing and negative charge has negative sing .
    gif.latex?V_%7Bab%7D%3D-%5Cint_%7Bb%7D%5E%7Ba%7D%28%5Cvec%7BE%7D.%5Cvec%7Bdl%7D%29.gif
    why in resistance equation we ignore negative sign?
     
  2. jcsd
  3. Apr 2, 2014 #2

    ehild

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    The voltage in Ohm's Law means potential drop, negative potential difference. The potential decreases in the direction of the electric field, and the current flows in the direction of the electric field.

    ehild
     
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