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Coulomb's law

What is the definition of Coulomb's law?
The force between two charged particles is perfectly proportional to the product of their charges and inversely proportional to the square of the distance between them. The direction of the interaction between the charges is determined by the straight line that runs through both charges. Two charges with equal values repel each other, whereas charges with opposite values attract each other.

Coulomb's law defines the value of the electrostatic force that acts between two charges. In its basic form, Coulomb's law is applied to point charges but can also be applied to two uniformly charged spheres.
This law was published in 1785, after many meticulous attempts at measurement. Couloub carried out his research on so-called ‘torsion balance’. This was a similar instrument to the one used several years later to measure gravitational forces.

The formula for Coulomb's Law:


where Fc = electrostatic force
k = electrostatic constant
q1 = electric charge of the first object
q2 = electric charge of the second object
r = the distance between charges or between centres of evenly charged spheres

What is the value of the electrostatic force?

Despite the fact that it is imperceptible on a daily basis, the electrostatic force is large. There are much greater forces between the particles, the electron and the proton than their gravitational forces. However, in the real world, the situation is exactly the opposite. It is much easier to perceive the gravitational force than the electrostatic force – mainly because the observed charges are usually balanced and have one charge equal to zero. The forces which interact between protons and electrons, on the other hand, act in a microscopic way which is inaccessible to the human eye.
It is known that the force increases with the value of the charges and the decrease in distance between them.

Coulomb's force is a vector quantity.
Coulomb discovered that charge essentially has two natures: positive and negative. Whether they attract or repel each other depends on which charges we are dealing with. It is still known today that objects with the same charge as another object – either positive or negative – will repel each other. Objects with different charges, on the other hand, will attract each other. The force studied by Coulomb, therefore, acts in two directions. But what happens if there are more than two objects? In which direction would the force then act? To this end, when presenting the formula for the electrostatic force, the discoverer of the law included an additional component to the equation, which is an indicator of the position of a specific, different charge.

History before the discovery of Coulomb's law.
Even in the old days, it was already known that by rubbing amber against fur, the amber gained the ability to attract smaller objects. Through many types of research on this phenomenon, it was possible to accumulate bigger and bigger charges and transfer them from one object to another by touch. All previous knowledge was limited to a series of experiments on ordinary objects until the discovery made by Charles Coulomb.
Inside a glass vessel, he suspended a needle on a thin thread. At one end, he placed a brass sphere and a counterweight at the other. This was to keep the needle in balance. Then he placed a second, charged sphere in the vessel. When the two spheres came into contact, the charges divided between them and they began to repel each other. By measuring the angle of the needle under different experimental conditions, he was able to describe the interaction between the charges of the force. This led him to formulate a law.

Thanks to Charles Coulomb's discovery, the world gained a great deal of knowledge about the various possible applications of electrostatic forces. These forces are used in many industries. The simplest example is electromagnets, which are used in many branches of the economy. Today, it is hard to imagine the world without this invention and it is thanks to this invention (among others) that French physicist Charles Coulomb, wrote down his ‘golden’ notes in the history of physics forever.


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