Coulomb's Law
$$ \vec{F}_Q = \frac{1}{4\pi\epsilon_0} \frac{q Q}{\rsep^2}\hatrsep $$
$\vec{r}'$
: source position of $q$
$\vec{r}$
: test position of $Q$
$\vecrsep$
= $\vec{r}-\vec{r}'$
Source charge $q$
+3
units
Test charge $Q$
+3
units
Positive charge
Negative charge
Separation vector $\vecrsep$
Unit vector $\hatrsep$
Distance $\rsep=|\vecrsep|$
Forces $\vec{F}_Q,\vec{F}_q$
Position vectors $\vec{r}',\vec{r}$
Like repel
Opposites attract
Double distance
Bigger charges