Electric Potential: Find x for Zero Net Electric Potential

  • #1



Homework Statement

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?

Homework Equations


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
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.
  • #3
But we are considering potential. Do we understand through electric field then use the equation of potential?
  • #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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