63. Charged bodies. Electrification by friction

Electromagnetic forces play a huge role in nature because all bodies are built from electrically charged particles. The most important components of the atom - the nucleus and electrons - have electrical charges.

A large body, as it is easy to imagine, is electrically charged if it contains an excess of elementary particles with the same charge sign. Negative charge of a body is caused by excess of electrons in comparison with protons, and positive - by their lack.

Most bodies in the normal state are electrically neutral: the number of electrons in them is equal to the number of protons. Neutral is the atom of any substance. The number of electrons in the shell of an atom is equal to the number of protons in the nucleus. Positively and negatively charged particles are connected with each other, forming neutral systems. It is not difficult to understand why most bodies are electrically neutral, charged bodies attract oppositely charged particles.

To get electrically charged macroscopic bodies, i.e. to electrify them, a part of the negative charge must be separated from the associated positive charge. The easiest way to do this is to use friction. If you brush several times on dry hair, then a small part of the most mobile charged particles - electrons - will go from hair to comb and will charge it negatively. Hair will then be positively charged. Appearance of the charge on the comb is very easy to detect, it will start to attract a light piece of paper.

When friction electrifies, the most important thing is not friction itself. What matters is the close contact between different substances.
In this contact, a small part of the electrons of the substance, for which the bond between the electrons and the piece of substance is relatively weak, are transferred to another substance. The displacement of electrons in this case does not exceed the dimensions of the interatomic distances of \(10^{-8} cm\). But if the bodies are now moved apart, they will both be charged.

Since the surfaces of bodies are never perfectly smooth, the close contact between the electrons necessary for the transition of electrons is only established on small areas of surfaces.
Friction of bodies against each other increases the number of areas with close contact and thus increases the total charge flowing from one body to another.

Electrification occurs when any body comes into contact with one another. But the best way to observe it is by friction of so-called insulators, i.e. bodies that do not conduct electricity. These bodies have charges that remain where they appeared during electrification. In conductors ( for example, in metal), the charge generated in a certain area can move to any other area. Therefore, when the pieces are separated, at the last moment all the excess electrons of one metal will move to another through the contact points that are separated last. After all, it is impossible to separate the pieces so that the contact is broken at the same time in all areas.