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Electric Potential

  1. May 18, 2009 #1

    Air

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    1. The problem statement, all variables and given/known data
    Particles of the charges q1=+5e (at origin) and q2=-15e are fixed in place with a separation of d=0.24m. With V=0 at infinity, what are the finite (a) positive and (b) negative values of x at which the net electric potential on the x axis is zero?


    2. Relevant equations
    E=Kq/r


    3. The problem I encounter
    I can get the answer but I don't understand the position considered. Where do I consider my x value to be? Why don't we consider x to be greater than d? Why do we only consider for 0<x<d or x<d?
     
  2. jcsd
  3. May 18, 2009 #2
    x is the point where the electric fields from the charges cancel each other out. There are only two such points. You can consider x>d if you like but you won't find a point where the fields cancel each other because the field of q2 is always stronger in that region.
     
  4. May 18, 2009 #3

    Air

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    But we are considering potential. Do we understand through electric field then use the equation of potential?
     
  5. May 18, 2009 #4
    Well, the only difference in the formula for the field is the power of r so qualitatively it's the same. In the region x>d the magnitude of q2 potential is always greater than that of q1. I just thought fields are more intuitive and illustrate better why there are only two points.
     
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