When electrifying, friction occurs. Electrification of tel. Two kinds of charges. Electric charge conservation law. Properties of electrified bodies

Even in ancient times it was known that if you rub amber on wool, it begins to attract light objects to itself. Later, the same property was found in other substances (glass, ebonite, etc.). This phenomenon is called electrification, and bodies capable of attracting other objects to themselves after rubbing are electrified. The phenomenon of electrification was explained on the basis of the hypothesis of the existence of charges that an electrified body acquires.

Simple experiments on the electrification of various bodies illustrate the following provisions.

• There are two types of charges: positive (+) and negative (-). A positive charge arises when glass is rubbed against leather or silk, and a negative $ - $ when amber (or ebonite) is rubbed against wool.
• Charges (or charged bodies) interact with each other. Like charges repel, unlike $ - $ attracts.

The state of electrification can be transferred from one body to another, which is associated with the transfer of electrical charge. In this case, a larger or smaller charge can be transferred to the body, that is, the charge has a magnitude. During electrification by friction, both bodies acquire a charge, one $ - $ positive, and the other $ - $ negative. It should be emphasized that the absolute values \u200b\u200bof the charges of bodies electrified by friction are equal, which is confirmed by numerous experiments.

It became possible to explain why bodies are electrified (i.e. charged) during friction after the discovery of the electron and the study of the structure of the atom. As you know, all substances consist of atoms, which, in turn, consist of elementary particles $ - $ negatively charged electrons, positively charged protons and neutral particles $ - $ neutrons. Electrons and protons are carriers of elementary (minimum) electric charges. Protons and neutrons (nucleons) make up the positively charged nucleus of the atom, around which negatively charged electrons revolve, the number of which is equal to the number of protons, so that the atom as a whole is electrically neutral. Under normal conditions, bodies consisting of atoms (or molecules) are electrically neutral. However, in the process of friction, part of the electrons that have left their atoms can move from one body to another. In this case, the movement of electrons does not exceed interatomic distances. But if, after friction, the bodies are disconnected, then they will be charged: the body that gave up some of its electrons will be positively charged, and the body that acquired them $ - $ negatively.

So, bodies are electrified, that is, they receive an electric charge when they lose or gain electrons. In some cases, electrification is due to the movement of ions. In this case, new electric charges do not arise. There is only a division of the existing charges between the electrifying bodies: a part of the negative charges passes from one body to another.

In the course of this lesson, we will continue to get acquainted with the "whales" on which electrodynamics stands - electric charges. We will study the electrification process, consider what principle this process is based on. Let's talk about two types of charges and formulate the conservation law for these charges.

In the last lesson, we already mentioned early experiments in electrostatics. All of them were based on rubbing one substance against another and further interaction of these bodies with small objects (dust particles, scraps of paper ...). All of these experiences are based on the electrification process.

Definition.Electrification- separation of electric charges. This means that electrons from one body go to another (Fig. 1).

Fig. 1. Separation of electric charges

Until the discovery of the theory of two fundamentally different charges and the elementary charge of an electron, it was believed that a charge is some kind of invisible super-light liquid, and if it is on the body, then the body has a charge and vice versa.

The first serious experiments on the electrification of various bodies, as already mentioned in the previous lesson, were carried out by the English scientist and physician William Hilbert (1544-1603), but he could not electrify metal bodies, and he considered that the electrification of metals was impossible. However, this turned out to be untrue, which was later proved by the Russian scientist Petrov. However, the next more important step in the study of electrodynamics (namely, the discovery of dissimilar charges) was made by the French scientist Charles Dufay (1698-1739). As a result of his experiments, he established the presence, as he called them, of glass (glass rubbing against silk) and resin (amber against fur) charges.

Some time later, the following laws were formulated (Fig. 2):

1) like charges are mutually repelled;

2) opposite charges are mutually attracted.

Fig. 2. Interaction of charges

The designations for positive (+) and negative (-) charges were introduced by the American scientist Benjamin Franklin (1706-1790).

By convention, it is customary to call a positive charge that forms on a glass rod if you rub it with paper or silk (Fig. 3), and a negative one - on an ebony or amber rod if you rub it with fur (Fig. 4).

Fig. 3. Positive charge

Fig. 4. Negative charge

Thomson's discovery of the electron finally made scientists understand that during electrification, no electric fluid is imparted to the body and no charge is applied from the outside. There is a redistribution of electrons, as the smallest carriers of a negative charge. In the region where they come, their number becomes larger than the number of positive protons. Thus, an uncompensated negative charge appears. Conversely, in the area from which they leave, there is a shortage of negative charges necessary to compensate for the positive ones. Thus, the area is charged positively.

It was established not only the presence of two different types of charges, but also two different principles of their interaction: the mutual repulsion of two bodies charged with the same charges (of the same sign) and, accordingly, the attraction of oppositely charged bodies.

Electrification can be done in several ways:

• friction;
• by touch;
• blow;
• guidance (through influence);
• irradiation;
• chemical interaction.

Electrification by friction and electrification by contact

When a glass rod is rubbed against paper, the rod is positively charged. In contact with the metal stand, the stick transfers a positive charge to the paper sultan, and its petals repel each other (Fig. 5). This experience suggests that charges of the same name are repelled from each other.

Fig. 5. Electrifying by touch

As a result of friction against fur, ebonite acquires a negative charge. Bringing this stick to the paper sultan, we see how the petals are attracted to it (see Fig. 6).

Fig. 6. Attraction of unlike charges

Electrification through influence (guidance)

We put a ruler on a stand with the Sultan. After electrifying the glass rod, bring it closer to the ruler. The friction between the ruler and the stand will be small, so you can observe the interaction of a charged body (stick) and a body that has no charge (ruler).

During each experiment, charge separation was performed, no new charges appeared (Fig. 7).

Fig. 7. Redistribution of charges

So, if we have communicated the electric charge to the body by any of the above methods, we, of course, need to estimate the magnitude of this charge in some way. For this, an electrometer device is used, which was invented by the Russian scientist M.V. Lomonosov (Fig. 8).

Fig. 8. M.V. Lomonosov (1711-1765)

The electrometer (Fig. 9) consists of a round can, a metal rod and a light rod that can rotate around a horizontal axis.

Fig. 9. Electrometer

When giving a charge to the electrometer, in any case (for both positive and negative charges) we charge both the rod and the arrow with the same charges, as a result of which the arrow is deflected. The charge is estimated from the deflection angle (Fig. 10).

Fig. 10. Electrometer. Deflection angle

If you take an electrified glass rod and touch it to the electrometer, the arrow will deviate. This indicates that an electrical charge has been imparted to the electrometer. In the course of the same experiment with an ebonite rod, this charge is compensated (Fig. 11).

Fig. 11. Compensation of the electrometer charge

Since it has already been indicated that no charge is created, but only redistribution occurs, it makes sense to formulate the law of conservation of charge:

In a closed system, the algebraic sum of electric charges remains constant(fig. 12). A closed system is a system of bodies from which charges do not leave and into which charged bodies or charged particles do not enter.

Fig. 13. Law of conservation of charge

This law reminds of the law of conservation of mass, since charges exist only together with particles. Charges are very often called by analogy the amount of electricity.

The law of conservation of charges has not been fully explained, since charges appear and disappear only in pairs. In other words, if charges are born, then only positive and negative at once, and equal in absolute value.

In the next lesson, we will dwell in more detail on quantitative assessments of electrodynamics.

List of references

1. Tikhomirova S.A., Yavorskiy B.M. Physics (basic level) - M .: Mnemosina, 2012.
2. Gendenshtein L.E., Dick Yu.I. Physics grade 10. - M .: Ileksa, 2005.
3. Kasyanov V.A. Physics grade 10. - M .: Bustard, 2010.

1. Internet portal "youtube.com" ()
2. Internet portal "abcport.ru" ()
3. Internet portal "planeta.edu.tomsk.ru" ()

Homework

1. P. 356: No. 1-5. Kasyanov V.A. Physics grade 10. - M .: Bustard. 2010.
2. Why does the needle of the electroscope deviate when touched by a charged body?
3. One ball is positively charged, the other negative. How will the mass of the balls change when they touch?
4. * Bring the charged metal rod to the ball of the charged electroscope, without touching it. How will the deflection of the arrow change?

Body electrify, i.e. get an electric chargewhen they gain or lose electrons. In this case, new electric charges do not arise. There is only a division of the existing charges between the electrifying bodies: some of the negative charges are transferred from one body to another.

Electrification methods:

1) electrification friction: dissimilar bodies are involved. The bodies acquire charges of the same modulus, but different in sign.

2) electrification contact: when a charged and an uncharged body comes into contact, part of the charge is transferred to the uncharged body, that is, both bodies acquire a charge of the same sign.

3) electrification through influence: with electrification through influence, you can get a negative charge on the body with a positive charge, and vice versa.

Knowledge about the electron and the structure of the atom makes it possible to explain the phenomenon of attraction of non-electrified bodies to electrified ones. Why, for example, is a cartridge case attracted to a charged stick, which we have not previously electrified? After all, we know that the electric field acts only on charged bodies.

If a charge is transferred from a charged ball to an uncharged ball and the sizes of the balls are the same, then the charge will split in half. But if the second, uncharged ball is larger than the first, then more than half of the charge will be transferred to it. The larger the body to which the charge is transferred, the more of the charge will be transferred to it. Grounding is based on this - the transfer of charge to the ground. The globe is large compared to the bodies on it. Therefore, upon contact with the ground, a charged body gives it almost all of its charge and practically becomes electrically neutral.