diff --git a/docs/physics/electrostatics/5-moving-charges.md b/docs/physics/electrostatics/5-moving-charges.md new file mode 100644 index 0000000..9376772 --- /dev/null +++ b/docs/physics/electrostatics/5-moving-charges.md @@ -0,0 +1,13 @@ +# Chapter 5 - Electrodynamics with Moving Charges + +## Section 5.1 - Currents in Steady-State Regine + +We want to work in a steady-state system. Thus, we restrict ourselves to currents that do not change in time. + +With math, we see that $\div \vb{J}(\vb{r}) = -\frac{\partial \rho(\vb{r})}{\partial t}$. Since we are only considering a steady-state system, $\div \vb{J}_e = \div \vb{J}_m = 0$. + +**Definition**. The *conductance* of a material is $G = \frac{1}{R}$, where $R$ is the resistance of a material. + +For a wire of uniform cross-sectional area, we see that $G = \sigma \frac{A}{L}$, where $A$ is the cross-sectional area, $L$ is the length of the wire, and $\sigma$ is the conductivity of a wire. Inverted, we see that $R$ = $\rho \frac{L}{A}$, where $\rho = \frac{1}{\sigma}$ is the resistivity of the wire. + +**Definition**. *Ohm's Law* can be written as $I = G V$, or inverted, $V = IR$. In a wire, we see that current density $\vb{} = \frac{I}{A} = \sigma \frac{V}{L} = \sigma \vb{E}$ \ No newline at end of file