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education/physics/PHYS2220/Electric Charge.md
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- The smallest discrete quantity of charge is $\frac{1}{3}e$. - The smallest discrete quantity of charge is $\frac{1}{3}e$.
- In an isolated system, the net charge will always remain constant. - In an isolated system, the net charge will always remain constant.
# Electric Force # Coulomb's Law
- Two charges will exert a force on each other along the line joining them. - Two charges will exert a force on each other along the line joining them.
- The magnitude of this force is proportional to the *product of the charges* and inversely proportional to the to the $\sqrt{dist}$. - The magnitude of this force is proportional to the *product of the charges* and inversely proportional to the to the $\sqrt{dist}$.
- The equation to determine the force between two charges is as follows: - The equation to determine the force between two charges is as follows:
$$ \vec{F_{12} = \vec{r}k\frac{q_1q_2}{r^2}} $$ $$ \vec{F}_{12} = \vec{r}k\frac{q_1q_2}{r^2} $$
- $\vec{r}$ is a unit vector pointing from charge 1 to charge 2 - $\vec{r}$ is a unit vector pointing from charge 1 to charge 2
- $k$ is Couloumb's constant, or $8.99 * 10^9 \frac{Nm^2}{C^2}$ - $k$ is Coulomb's constant, or $8.99 * 10^9 \frac{Nm^2}{C^2}$
- $q_1$ and $q_2$ - $q_1$ and $q_2$ are the charges
- $r$ is the distance between those charges
- The resulting force will push away if $q_1q_2$ is *positive*, and attract if $q_1q_2$ is negative. This is where the rule "opposites attract, like repels" comes from
- Coulomb's law only holds exactly true for *point charges* i.e a proton