# Difference between revisions of "Coulomb law"

Coulomb law is fundamental scientific concept about interaction of electric charges.

The special conserving quantity is postulated, called electric charge.

Potential energy of interaction of two charges $q_1$ and $d_2$ localised in regions small compared to the distance $r$ between them, is postulated to be

$\displaystyle U=k \frac{q_1 q_2}{r}$

where $k$ is fundamental constant determined by unit of measurement of the electric charge.

In the system SI, unit of charge is Coulomb, and

$\displaystyle k=\frac{1}{4 \pi \varepsilon_0} \approx 8.9875517873681764\times 10^9 \mathrm{Newton\, Meter^2\, Coulomb}^{-2}$

## Do physicians know physics?

Since century 20, the popular questions for students of medical institutes was: How many physicians know physics?

The similar question refer to Mathematica with respect to the example below:

Needs["PhysicalConstants"]
VacuumPermittivity
N[VacuumPermittivity]
ElectronCharge
ElectronCharge^2/(4 Pi VacuumPermittivity  )
`

The last line produces output $\mathrm{ (2.30708\times 10^{-28} Coulomb^2~ Meter~ Volt)/(Ampere~ Second) }$

$\mathrm{ 2.30708\times 10^{-28}~ Joule~ Meter }$