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=====Electric Charge and Electric Field=====
The charge of the electron is ''q<sub>e</sub> = &minus;e'', where the [[w:Elementary charge|fundamental charge]] is {{nowrap begin}}''e&asymp;1.6 x 10<sup>&minus;19</sup> C''{{nowrap end}}.  (''C&equiv;Coulombs'' is the SI unit of charge).
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*<math>F=k\frac{|q_1q_2|}{r^2}</math> is [[w:Coulomb's law|Coulomb's law]] for the force between two point charges ''q<sub>1</sub>'' and ''q<sub>2</sub>'' separated by a distance ''r''.  [[w:Coulomb's constant|Coulomb's constant]] is ''k &asymp;'' {{nowrap begin}}''8.99x10<sup>9</sup> N m<sup>2</sup> C<sup>&minus;2</sup>''.{{nowrap end}}
*<math>\vec F = q_t\vec E</math> if the force on a test charge ''q<sub>t</sub>'' due to the electric field <math>\vec E=\Sigma \vec E_j</math> at the location of the [[w:Test particle|test charge]].  The vector sum is over <math>n=1\rightarrow N</math> source charges, and the magnitude of each contribution to the field is <math>|\vec E_n| = kq_n/r_{nt}^2</math> where ''q<sub>n</sub>'' is the source charge and ''r<sub>nt</sub>'' is the distance from the source point to the test charge.<ref>For more information about this sum, see [[w:Special:Permalink/791000226#Superposition_principle]].</ref>
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<section begin=Electric Potential and Electric Field/>
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