Is it possible to charge with friction electrification. Explanation of electrical phenomena (Grebenyuk Yu.V.)
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 of 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 charged positively, 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: some of the negative charges are transferred 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 experiments are based on the electrification process.
Definition.Electrification- separation of electric charges. This means that electrons from one body go to another (Fig. 1).
Rice. 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 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) unlike charges are mutually attracted.
Rice. 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).
Rice. 3. Positive charge
Rice. 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.
Rice. 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).
Rice. 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).
Rice. 7. Redistribution of charges
So, if we have communicated the electric charge to the body in any of the above ways, 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).
Rice. 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 horizontally located axis.
Rice. 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).
Rice. 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).
Rice. 11. Electrometer charge compensation
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.
Rice. 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 the charges are born, then only positive and negative at once, and equal in magnitude.
In the next lesson, we will dwell in more detail on quantitative assessments of electrodynamics.
Bibliography
- Tikhomirova S.A., Yavorskiy B.M. Physics (basic level) - M .: Mnemosina, 2012.
- Gendenshtein L.E., Dick Yu.I. Physics grade 10. - M .: Ileksa, 2005.
- Kasyanov V.A. Physics grade 10. - M .: Bustard, 2010.
- Internet portal "youtube.com" ()
- Internet portal "abcport.ru" ()
- Internet portal "planeta.edu.tomsk.ru" ()
Homework
- P. 356: No. 1-5. Kasyanov V.A. Physics grade 10. - M .: Bustard. 2010.
- Why does the needle of the electroscope deviate when touched by a charged body?
- One ball is positively charged, the other negative. How will the mass of the balls change when they touch?
- * Bring the charged metal rod to the ball of the charged electroscope, without touching it. How will the deflection of the arrow change?
The phenomena associated with electricity are quite common in nature. One of the most observable phenomena is the electrification of bodies. One way or another, every person had to deal with electrification. Sometimes we do not notice static electricity around us, and sometimes its manifestation is pronounced and quite noticeable.
For example, car owners, under certain circumstances, noticed how their car suddenly began to "shock". This usually happens when leaving the vehicle. At night, you can even notice sparking between the body and the hand touching it. This is explained by electrification, which we will talk about in this article.
Definition
In physics, electrification is called the process in which there is a redistribution of charges on the surfaces of dissimilar bodies. In this case, charged particles of opposite signs accumulate on the bodies. Electrified bodies can transfer part of the accumulated charged particles to other objects or the environment in contact with them.
A charged body transfers charges upon direct contact with neutral or oppositely charged objects, or through a conductor. As the redistribution progresses, the interaction of electric charges is balanced, and the overflow process stops.
It is important to remember that when bodies are electrified, new electrical particles do not arise, but only existing ones are redistributed. During electrification, the law of conservation of charge operates, according to which the algebraic sum of negative and positive charges is always zero. In other words, the number of negative charges transferred to another body during electrification is equal to the number of remaining charged protons of the opposite sign.
It is known that the carrier of an elementary negative charge is an electron. Protons, on the other hand, have positive signs, but these particles are firmly bound by nuclear forces and cannot move freely during electrification (except for the short-term release of protons during the destruction of atomic nuclei, for example, in various accelerators). In general, an atom is usually electrically neutral. Electrification can disrupt its neutrality.
However, individual electrons from the cloud surrounding multiproton nuclei can leave their distant orbits and move freely between atoms. In such cases, ions (sometimes called holes) are formed that have positive charges. See diagram in fig. 1.
Rice. 1. Two kinds of charges
In solids, ions are bound by atomic forces and, unlike electrons, cannot change their position. Therefore, only electrons are charge carriers in solids. For clarity, we will consider ions as simply charged particles (abstract point charges), which behave in the same way as particles with the opposite sign - electrons.
Rice. 2. Model of the atom Physical bodies in natural conditions are electrically neutral. This means that their interactions are balanced, that is, the number of positively charged ions is equal to the number of negatively charged particles. However, electrification of the body upsets this balance. In such cases, electrification is the reason for the change in the balance of the Coulomb forces.
Conditions for the occurrence of electrification of bodies
Before proceeding to the definition of the conditions for electrization of bodies, let us focus your attention on the interaction of point charges. Figure 3 shows a diagram of this interaction.
Rice. 3. Interaction of charged particles The figure shows that the like-named point charges repel, while the opposite ones attract. In 1785, the forces of these interactions were investigated by the French physicist O. Coulomb. The famous one says: two stationary point charges q 1 and q 2, the distance between which is r, act on each other with a force:
F = (k * q 1 * q 2) / r 2
The coefficient k depends on the choice of the measurement system and the properties of the medium.
Proceeding from the fact that Coulomb forces act on point charges, which have an inversely proportional dependence on the square of the distance between them, the manifestation of these forces can be observed only at very small distances. In practice, these interactions manifest themselves at the level of atomic dimensions.
Thus, in order for the electrification of a body to occur, it is necessary to bring it as close as possible to another charged body, that is, to touch it. Then, under the action of Coulomb forces, part of the charged particles will move to the surface of the charged object.
Strictly speaking, during electrification, only electrons move, which are distributed over the surface of the charged body. An excess of electrons forms a certain negative charge. The creation of a positive charge on the surface of the recipient, the electrons from which flowed to the charged object, is assigned to the ions. In this case, the absolute values of the charges on each of the surfaces are equal, but their signs are opposite.
Electrization of neutral bodies from dissimilar substances is possible only if one of them has very weak electronic bonds with the nucleus, while the other, on the contrary, is very strong. In practice, this means that in substances in which electrons rotate in distant orbits, some of the electrons lose their bonds with nuclei and interact weakly with atoms. Therefore, during electrification (close contact with substances), in which stronger electronic bonds with nuclei are manifested, a flow of free electrons occurs. Thus, the presence of weak and strong electronic bonds is the main condition for the electrification of bodies.
Since ions can also move in acidic and alkaline electrolytes, electrification of a liquid is possible by redistributing its own ions, as is the case in electrolysis.
Methods for electrifying bodies
There are several methods of electrification, which can be conditionally divided into two groups:
- Mechanical impact:
- electrification by contact;
- electrification by friction;
- electrification on impact.
- Influence of external forces:
- electric field;
- exposure to light (photoelectric effect);
- the influence of heat (thermocouples);
- chemical reactions;
- pressure (piezoelectric effect).
Rice. 4. Methods of electrification The most common way of electrifying bodies in nature is friction. Most often, air friction occurs when it comes into contact with solid or liquid substances. In particular, lightning discharges occur as a result of such electrification.
We have known electrification by friction since school days. We could observe small ebony sticks electrified by friction. The negative charge of the sticks rubbed against the wool is determined by the excess of electrons. In this case, the woolen fabric is charged with positive electricity.
A similar experiment can be carried out with glass rods, but they must be rubbed with silk or synthetic fabrics. At the same time, as a result of friction, electrified glass rods are charged positively, and the fabric - negatively. Otherwise, there is no difference between glass electricity and ebonite charge.
To electrify a conductor (for example, a metal rod), you must:
- Insulate a metal object.
- Touch it with a positively charged body, such as a glass rod.
- Take some of the charge to ground (ground one end of the rod for a short time).
- Remove the charged stick.
In this case, the charge on the rod is evenly distributed over its surface. If a metal object is irregular in shape, uneven, the concentration of electrons will be greater at the bulges and less at the depressions. When bodies are separated, a redistribution of charged particles occurs.
Properties of electrified bodies
- Attraction (repulsion) of small objects is a sign of electrification. Two bodies, charged with the same name, counteract (repel), and different signs attract. This principle is the basis for the operation of an electroscope - a device for measuring the amount of charge (see Fig. 5).
Rice. 5. Electroscope - Excess charges upset the balance in the interaction of elementary particles. Therefore, each charged body seeks to get rid of its charge. Often this release is accompanied by a lightning discharge.
Application in practice
- air purification with electrostatic filters;
- electrostatic painting of metal surfaces;
- production of synthetic fur by attracting electrified pile to a fabric base, etc.
Harmful effects:
- the effect of static discharges on sensitive electronic products;
- ignition of vapors of fuels and lubricants from discharges.
Ways to combat: grounding containers with fuel, work in antistatic clothing, grounding tools, etc.
Video in addition to the topic
Why don't we observe electric forces of attraction and repulsion between the bodies around us? After all, all bodies are made of atoms, and atoms are made of particles with electric charges.
The reason is that atoms in general are neutral. The total negative charge of all electrons in an atom is equal to the positive charge of the nucleus. The total charge of an atom is zero. And since the atom is neutral, the molecule is also neutral. And a body composed of atoms or molecules is also neutral; it has no electrical charge.
Take a glass rod and rub it hard with a piece of dry silk. In this case, part of the electrons is detached from the glass molecules and goes to the silk molecules. The so-called ionization of some glass molecules occurs, their transformation from neutral particles into electrically charged particles - ions. Glass molecules that have lost one or more electrons are no longer neutral. The positive charge of the nuclei in such a molecule is greater than the negative charge of the electrons remaining in it. The molecule is positively charged - it is a positive ion. An atom or molecule that has captured one or more extra electrons is called negative ions.
If you touch this stick to two sheets of tissue paper suspended by threads, then some of the electrons from the sheets will be attracted by the positively charged stick and will transfer to it. The leaves will charge positively and begin to repel each other, as shown in Figure 3.
Leaves can also be charged negatively. To do this, instead of glass, you need to take an ebonite or wax stick, and instead of silk - fur or woolen cloth. When rubbing wax or ebonite with fur, some of the electrons are transferred from the fur to the stick and it is charged negatively. Electrons repel each other. Therefore, when the stick touches the piece of tissue paper,
Some of the electrons are transferred to it. Two leaves, which we touch with an ebonite or wax stick, are charged negatively. They repel each other in the same way as shown in Figure 3, and are attracted to the positively charged leaves (Figure 4).
For the first time, people got acquainted with electricity, rubbing amber with wool. It was in ancient Greece two and a half thousand years ago. Amber is called "electron" in Greek. This is how the word "electricity" was born.
We now see that the electrical properties of amber, glass, ebonite and other bodies that people have become acquainted with through experience are only a manifestation of the electrical forces acting between electrons and nuclei.
The names "positive" and "negative" charges were given when nothing was known about the structure of the atom, about electrons and nuclei. Subsequently, it turned out that the nuclear charge was called positive, and the electron charge was called negative.
A positively charged body is a body that has lost some of its electrons. A negatively charged body is a body that has acquired excess electrons. Electrization of bodies during friction is caused by the transfer of a part of electrons from one body to another.
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Body electrify, i.e. get an electric charge when 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.
Friction electrification is explained by the transfer of part of the electrons from one body to another, as a result of which the bodies are charged differently. Bodies electrified by rubbing against each other are attracted. Induction electrification is explained by the redistribution of the electron gas between bodies (or body parts), as a result of which the bodies (or body parts) are charged differently. However, the question arises: do all bodies lend themselves to electrification by induction? Experiments can be done to see that plastic, wood or rubber balls can easily be electrified by friction, but not induction.
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 that we had not previously electrified attracted to a charged stick? 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.
