# Electricity and Magnetism

# PHYS 102

Electricity and magnetism are related to the existence and motion of electric charges.

$e = 1.6 \times {10}^{-19} C$

$k = 9 \times {10}^9 N/C^2$

$\vec F_{1 \text{ on } 2} = \frac{k q_1 q_2}{r^2} \hat{r}$

$\vec F_{1 \text{ on } 2} = -\vec F_{2 \text{ on } 1}$

$\vec F_P = \sum_i \vec F_{i \text{ on }P} = \int_{q_0}^{q_f} \frac{k q_P}{r^2} \cdot dq \hat{r}$

**Law of conservation of charge**: the amount of charge in a region cannot change except by charges flowing across the boundary of the region.

A flow of charges is called **current**.

- conductor
- insulator
- (semiconductor)
- (superconductor)

Both insulators and conductors can be charged. When charges are placed on conductors, they repel each other and spread out to minimize electrostatic potential energy.

The electric field of a point charge $q$ is $\vec E = \frac{kq}{r^2} \hat{r}$. $\hat{r}$ points from the point charge to the point of interest, and is placed at the point of interest. Electric fields exist regardless of the presence of a second charge.

$F_{1 \text{ on } 2} = q_2 \vec E_{1 \text{ at } q_2}$