Coulomb's law

Charles Augustin de Coulomb

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

This picture shows how Coulomb's Force act; similar charges pushing against each other and opposite charges attract each other

Let's think two electric charges exist in an empty space. If 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 magnetics 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, such as magnetics make a magnetic field. When both electric charges make their own field, as two fields will exist in one space at the same time, and they will make force to each other. The force they make to each other is called Coulomb's force or 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.

$F = {K_c}\frac{q_1q_2}{r^2}$

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

$q_1$ and $q_2$ are the scales of each electric charge. $r$ is the distance between the two electric charges. And $K_c$ has a certain value. It does not change relative to $q_1$ , $q_2$ or $r$. While ${K_c}$ remains constant, when multiples of $q_1$ and $q_2$ become bigger, the electrostatic force will also get bigger. When the distance $r$ become bigger, the electrostatic force will become smaller to ratio of $\frac{1}{r^2}$.
The exact size of $K_c$ is $\begin{align} k_c &= 8.987\ 551\ 787\ \times 10^9 \\ \end{align}$ $\approx 9 \times 10^9$N m² C^-2 (or m F^-1). This constant is called as Coulomb's Force Constant or Electrostatic Force Constant.

Inverse-square law

The relation between the force F and the distance $r$ follows the Inverse-square Law. Inverse-square law means that when the distance $r$ grows bigger, electrostatic force will become smaller by the ratio $\frac{1}{r^2}$. Gravitation, Electromagnetic radiation, Sound Intensity also follows this law.

Other pages

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

Other websites

• Coulomb's Law on Project PHYSNET.
• A maze game for teaching Coulomb's Law