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# Coulomb's law

Electromagnetism |
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Electricity · Magnetism |

**Coulomb's law** is a function developed in the 1780s by physicist Charles-Augustin de Coulomb. It explains how strong the force will be between two electrostatic charges. Electrostatic means electric charges without any motion.

## Direction

Let's think of two electric charges existing in an empty space. If the two charges are opposite, (+) and (-) charges for example, they will attract each other. And if two charges are both the same, both (+) or both (-) for example, they will push each other. This is similar to how magnets act, as N and S attract each other, and as N and N, S and S push each other.

This is because electric charges make an electric field. If two fields exist in the same space at the same time, then the two fields exert (~ put) force on each other. The force they make on each other is called 'Coulomb's force' or the **electrostatic force**. Coulomb's law explains how big the force will be.

## Scale

Coulomb's law explains the scale between two electric charges. The scale of electrostatic force follows the function below.

- [math]F = {K_c}\frac{q_1q_2}{r^2}[/math]

Coulomb's law explains that the force scale F is relative to ratio of [math]q_1,q_2[/math],[math]\frac{1}{r^2}[/math].

[math]q_1[/math] and [math]q_2[/math] are the scales of each electric charge. [math]r[/math] is the distance between the two electric charges. And [math]K_c[/math] has a certain value. It does not change relative to [math]q_1[/math], [math]q_2[/math] or [math]r[/math]. While [math]{K_c}[/math] remains constant, when multiples of [math]q_1[/math] and [math]q_2[/math] become bigger, the **electrostatic force** will also get bigger. When the distance [math]r[/math] becomes bigger, the electrostatic force will become smaller by the ratio of [math]\frac{1}{r^2}[/math].

The exact size of [math]K_c[/math] is
[math]
\begin{align}
k_c &= 8.987\ 551\ 787\ \times 10^9 \\
\end{align}
[/math]
[math] \approx 9 \times 10^9[/math]N m^{2} C^{−2} (or m F^{−1}). This constant is called **Coulomb's force constant** or the electrostatic force constant.

## Inverse-square law

The relation between the force of pushing or pulling (F) and the distance between the particles ([math]r[/math]) follows the Inverse-square Law. Inverse-square law means that when the distance [math]r[/math] grows bigger, the force gets weaker by the ratio [math]\frac{1}{r^2}[/math]. Gravitation, Electromagnetic radiation, and sound loudness also follow this law.

## Related pages

- Coulomb, the SI unit of electric charge named after Charles-Augustin de Coulomb
- Inverse-square law, the physical law that shows the relation between distance and Intensity.
- Electrostatic
- Magnetic