The Coulomb Law

If you transfer an electric positive or negative charge to an uncharged electroscope, you will notice that the leaves of the electroscope will diverge to a smaller or larger angle.

Touch with an electrified rod to the rod of the electroscope and remember the angle at which the leaves will diverge. In order to give the discrepancy of the leaves of the electroscope to a larger angle, it is necessary to transfer the charge from a larger area of the charged rod to it. And, conversely, the leaves will converge, when you touch the rod of an electroscope with your hand.

Thus, we find that the electric charge on the bodies is more or less. Consequently, we can talk about such a concept as the magnitude of the charge, and therefore, about its measurement.

This became possible thanks to the discovery in the late 18th century. Law on the interaction of electric charges. This law was discovered by the French physicist Coulomb.

Coulomb's law was discovered experimentally: the scientist conducted experiments with torsion scales, by which he measured the force with which electrified objects interact.

The torsion balance consists of a light, non-conductive electric charge of a rocker suspended on a very thin metal thread in a glass vessel of cylindrical shape. At one end of the rod, a gilded ball of cork is fixed, and on the other - a counterweight. At its top end, the wire is attached to the center of the head, provided with a pointer and rotating on a scale having a division, which serves to determine the size of the twisting angle of the fixed wire.

The lid of the vessel has a hole through which another, exactly the same ball b, which is equal to the ball a in size, is fed to the insulator. The size of the angular distance between the gilded balls a and b is calculated by the divisions that are on the cylindrical vessel. To do this, turn the head of the balance to a certain angle, you can change the distance.

After both balls are charged and installed at any distance, the pendant could determine the force with which these balls interact by measuring the twist angle of the filament.

If the device is pre-graduated, then by measuring the rotation angle of the head, it is possible to find out with what force the electrified balls interact.

When changing the distance between the balls, Coulomb found that at constant charges the force with which they interact will be inversely proportional to the double distance between their centers.

The solution of the problem of measuring the magnitude of the charges on the balls was as follows: if the ball b is charged and, having taken out of the device, contact with another ball, then exactly half the charge will go to the other ball from the ball b. Thus, the charge will remain half that. Putting the ball b back into the device, Coulomb found that at the same distance between the balls, their interaction force is halved - directly proportional to the reduction in the charge.

Similarly, the charge of the moving ball a varied.

Thanks to these experiments, a law was discovered that later became known as the Coulomb law, its definition is the following: the force of interaction of two point charges is directly proportional to their magnitudes, inversely proportional to the square of the distance between charges and directed along the line that connects these charges.

The law of Coulomb Amonton is expressed by the formula:

F = k (q1q2 / r²),

Where q1 and q2 are the values of the point charges that interact, r is the distance between these charges, and k is the proportionality coefficient, which depends on which units of measurement the quantities will enter into the formula.

In this case, such charges are called point charges that are on bodies of any size and shape that are sufficiently small in comparison with the distances at which their interaction is considered.

Studies have shown that the force F is influenced by the environment, and the formula that expresses the Coulomb law applies only when interacting charged bodies in a vacuum.

Thanks to the Coulomb law, a unit of electrical discharge was installed. So, it means a charge acting in a vacuum on an identical charge, which is a distance of one centimeter, with a force of one dyne. This is an absolute electrostatic charge unit.