# 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.