Homework Help: Question about vectors with electric field equations

1. Jan 18, 2005

LakeMountD

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. Jan 18, 2005

dextercioby

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

$$\vec{E}=\frac{q}{4\pi\epsilon_{0}\epsilon_{r}|\vec{r}|^{2}}\frac{\vec{r}}{|\vec{r}|}$$

That's all.

Daniel.

3. Jan 18, 2005

Tide

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.