[[Electric Force, Field, and Potential]]
# Summary
* Charge is quantized, integer multiple of $e=1.6x10^{-19}$.
* $q=\pm ne$
* Coulomb's law: $F=k\frac{p_1p_2}{n^2}$; directly proportional to charge, inversely proportional to distance.
* Same signs repel, opposite signs attract.
* Electric force is stronger than gravity for tiny particles, gravity controls large scale because big objects are usually neutral.
* Electric permittivity measures how much a material polarizes in a field. Conductors let charge move freely, insulators don't.
* Only need to calculate force for 4 or less interacting charges unless situation is highly symmetrical.