Key Equations

18.2 Coulomb's law

Coulomb’s law

$$F=\frac{k{q}_1{q}_2}{r^2}$$

18.3 Electric Field

electric field	$\overrightarrow{E}=\frac{\overrightarrow{F}}{q_{\text{test}}}$
magnitude of electric field of point charge	$$E=\frac{k\left|Q\right|}{r^2}$$

18.4 Electric Potential

change in electric potential energy for a charge that moves in a constant electric field	$\Delta U_{\text{E}}=-qE\left(x_{\text{f}}-x_{\text{i}}\right)$
electric potential energy of a charge a distance r from a point charge or sphere of uniform charge	$U_{\text{E}}=\frac{kQq}{r}$
definition of electric potential	$V=\frac{U_{\text{E}}}{q}$
change in electric potential for a charge that moves in a constant electric field	$\Delta V=-E\left(x_{\text{f}}-x_{\text{i}}\right)$
electric potential of a charge a distance r from a point charge or sphere of uniform charge	$V=\frac{kQ}{r}$

18.5 Capacitors and Dielectrics

capacitance	$C=\frac{Q}{V}$
energy stored in a capacitor	$U_E=\frac{1}{2}C{V}^2$
capacitance of a parallel-plate capacitor	$C=\kappa {\epsilon }_0\frac{A}{d}$