The electric field at a point in a region is given by $\vec{E} = \alpha \frac{\vec{r}}{|\vec{r}|^3}$, where $\alpha$ is a constant and $r$ is the distance of the point from the origin. The magnitude of potential of the point is : (A) $\frac{\alpha}{r}$ (B) $\frac{\alpha r^2}{2}$ (C) $\frac{\alpha}{2r^2}$ (D) $-\frac{\alpha}{r}$