Coulomb's law
| Electromagnetism |
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| Electricity · Magnetism · Magnetic permeability |
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]\displaystyle{ 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]\displaystyle{ q_1,q_2 }[/math],[math]\displaystyle{ \frac{1}{r^2} }[/math].
[math]\displaystyle{ q_1 }[/math] and [math]\displaystyle{ q_2 }[/math] are the scales of each electric charge. [math]\displaystyle{ r }[/math] is the distance between the two electric charges. And [math]\displaystyle{ K_c }[/math] has a certain value. It does not change relative to [math]\displaystyle{ q_1 }[/math], [math]\displaystyle{ q_2 }[/math] or [math]\displaystyle{ r }[/math]. While [math]\displaystyle{ {K_c} }[/math] remains constant, when multiples of [math]\displaystyle{ q_1 }[/math] and [math]\displaystyle{ q_2 }[/math] become bigger, the electrostatic force will also get bigger. When the distance [math]\displaystyle{ r }[/math] becomes bigger, the electrostatic force will become smaller by the ratio of [math]\displaystyle{ \frac{1}{r^2} }[/math].
The exact size of [math]\displaystyle{ K_c }[/math] is
[math]\displaystyle{
\begin{align}
k_c &= 8.987\ 551\ 787\ \times 10^9 \\
\end{align}
}[/math]
[math]\displaystyle{ \approx 9 \times 10^9 }[/math]N m2 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]\displaystyle{ r }[/math]) follows the Inverse-square Law. Inverse-square law means that when the distance [math]\displaystyle{ r }[/math] grows bigger, the force gets weaker by the ratio [math]\displaystyle{ \frac{1}{r^2} }[/math]. Gravitation, Electromagnetic radiation, and sound loudness also follow this law.
Coulomb's Law Media
The magnitude of the electrostatic force F between two point charges q1 and q2 is directly proportional to the product of the magnitudes of charges and inversely proportional to the square of the distance between them. Like charges repel each other, and opposite charges attract each other.
Coulomb's torsion balance
If two charges have the same sign, the electrostatic force between them is repulsive; if they have different sign, the force between them is attractive.
The most basic Feynman diagram for QED interaction between two fermions
Experiment to verify Coulomb's 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
Other websites
- Coulomb's Law on Project PHYSNET.
- A maze game for teaching Coulomb's Law Archived 2009-05-05 at the Wayback Machine