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Homework Help: Question about vectors with electric field equations

  1. Jan 18, 2005 #1
    Using the equation E= (kq)/(R)^2 in the r direction. I am confused on when to make the vector negative in my equations. For instance if you had a charge on x=0 and x=5 (on the x axis) and then you want to find the field at point (1,1) or something like this.
  2. jcsd
  3. Jan 18, 2005 #2


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    Consider an electric charge "q" in the origin of the coordinate system.The electric field at at a point of coordinate vector [tex] \vec{r} [/tex] is

    [tex] \vec{E}=\frac{q}{4\pi\epsilon_{0}\epsilon_{r}|\vec{r}|^{2}}\frac{\vec{r}}{|\vec{r}|} [/tex]

    That's all.

  4. Jan 18, 2005 #3


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    The direction of the vector is the same as the direction from the source point to the field point - multiplied by the sign of the charge.
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