Did you have fun as a child with such a simple trick: if you rub an inflated balloon on your dry hair and then apply it to the ceiling, it will seem to “stick”?
No? Try it, it's funny. No less funny is the hair sticking out in all directions. The same effect is sometimes obtained when combing long hair. They stick out and stick to the comb. Well, everyone is familiar with situations when, walking around in woolen or synthetic things, you touch something or someone and feel a sharp prick. In such cases they say - you get an electric shock. These are all examples electrification of bodies. But where does electrification come from, if we all know perfectly well that electricity lives in sockets and batteries, and not in hair and clothes?
The phenomenon of electrification of bodies: methods of electrification
The phenomenon of electrification of bodies begins to be studied in the eighth grade. And they begin the study by considering the electrification of bodies upon contact. To do this, experiments are carried out in lessons using the simplest methods of electrifying bodies by rubbing an ebonite or glass rod against fur or silk. You can do such experiments yourself; instead of a stick, you can take a plastic pen or ruler. Rub the pen on the wool or fur, and then bring it to finely cut pieces of paper, straws or hairs. You will see these pieces being attracted to the handle. The same thing will happen with a thin stream of water if you bring an electrified handle to it.
Two kinds of electric charges
First similar effects have been found with amber, that’s why they were called electric from the Greek word “electron” - amber. And the ability of bodies to attract other objects after contact, and rubbing is just a way to increase the area of contact, was called electrification or giving the body an electric charge. It has been experimentally established that There are two kinds of electric charges. If you rub glass and ebonite rods, they will attract each other. And two are the same - push off. And this happens not because they don’t like each other, but because they have different electrical charges. It was agreed upon to call the electric charge of a glass rod positive, and that of an ebonite rod negative. They are designated, respectively, by the signs “+” and “-”. Again, these names are not taken in the sense that one type of charge is good and the other is bad. This means that they are opposite to each other.
Nowadays, easily electrified objects are widely used - plastics, synthetic fibers, petroleum products. When such substances rub, an electric charge arises, which is sometimes at least unpleasant, and at most it can be harmful. In industry they are fought with special means. In everyday life the same an easy way to get rid of electrification- this is to moisten the electrified surface. If water is not at hand, touching metal or the ground will help. These bodies will remove the electrification. And in order not to experience these unpleasant effects at all, it is recommended to use antistatic agents.
§ 1 Electrification of bodies
In this lesson we will discuss the concept of electricity and find out where this word came from.
Now it is impossible to imagine the modern world without electricity, and even more so without a computer, refrigerator, TV, electric lighting, etc. All of the above-mentioned devices operate using electric current and surround us everywhere in our lives. Technologies that initially did not depend entirely on electricity, such as the internal combustion engine, are gradually becoming history; electric motors are actively taking their place. So where did such a word as “electricity” come from?
The word “electric” comes from the word “electron” (Greek), which means “amber” (fossil resin). Although, of course, it should be noted that there is no direct connection between amber and all electrical phenomena, so how did such an association appear among ancient scientists?
According to one legend, the daughter of a famous philosopher Ancient Greece Thales of Miletus, who lived in IV BC, spun wool with a spindle made of an expensive stone - amber. She told Thales that she could not clean the spindle from small pieces of wool, fluff, and thread. Moreover, the more she cleans her woolen chiton, the more debris sticks to the spindle. Thales could not immediately answer his daughter’s question.
In the evening, he decided to try to clean the spindle and saw that when rubbing it in the dark, sparks were visible. “This is something to think about and reflect on with my students,” Thales said.
The phenomenon that was noticed by the girl was called electricity by Thales (from the word electron - “amber”).
When you rub a piece of amber on a woolen piece of cloth or a glass rod on paper, you can hear a slight crackling sound, and in the dark you can even see small sparks, and the rod itself helps attract small objects to itself.
A body that attracts other bodies to itself after being rubbed is said to be given an electric charge or to be electrified.
Electrification is a phenomenon in which bodies acquire the properties of attracting other bodies.
Bodies made from different substances can become electrified. Thus, one can easily electrify by rubbing sticks made of sulfur, ebonite, or plastic on wool. The bodies are rubbed only to increase the area of their contact.
Two bodies are always involved in electrification, and both are electrified. Thus, when a glass rod and a piece of paper are rubbed, both the rod and the paper become electrified. Consequently, paper, like glass, attracts small objects.
A body has an electric charge that attracts or repels other bodies. Such a body is said to be charged (has a charge).
Charge is a property of bodies or the ability for electromagnetic interaction.
An electroscope is a device that allows you to detect the presence of a charge in a body and evaluate it.
The conductive insulated rod is the main part of the electroscope; a pointer is attached to it, which can rotate freely. When a charge appears, the arrow and the rod are charged with charges of the same sign, as a result of which they, when repelling, create a deflection angle, the value of which is proportional to the charge received.
§ 2 Methods of electrifying bodies
Electrification of bodies occurs in various cases.
Methods of electrifying bodies:
·contact
Let's look at some of them.
Ebonite will receive a negative charge, and wool will receive a positive charge, if you rub the ebonite stick on the wool. Using an electroscope, the presence of these charges is detected. To achieve this result, you need to touch the electroscope rod with an ebonite stick or woolen rag. In this case, part of the charge of the test body passes to the rod. Please note that a short-term electrical current occurs.
You can consider the interaction of two paper cartridges suspended on a thread, one charged from an ebonite stick, and the other from a woolen rag.
Note that they are attracted to each other. This means that bodies with opposite charges attract. Not every substance can transmit electrical charges.
Conductors are substances through which charges are transferred, and substances through which charges are not transferred are called non-conductors - dielectrics (insulators). This can be found out using an electroscope if you connect it to a charged body or substances of various kinds.
When describing electrification by friction, only good insulators are always taken for experiments - amber, ebonite, glass, silk. The question is why? Let us explain: in insulators the charge where it arose remains there and cannot pass through the entire surface of the body to other bodies in contact with it. If both rubbing bodies are metals with isolated handles, then the experiment will fail, since it is impossible to separate them from each other over the entire surface at once.
Due to the roughness of the surface of the bodies at the moment of separation, some last points contacts through which excess electrons escape at the last moment, and both metals become uncharged.
Let's consider electrification by contact. If we immerse a ball of paraffin in distilled water and then take it out, both the paraffin and the water will be charged.
So why did the electrification of water and paraffin occur without friction? Let us explain: it turns out that during electrification by friction, the area of contact only increases and the distance between the atoms of the rubbing bodies decreases. In an experiment with water and paraffin, roughness cannot prevent their atoms from approaching each other.
Thus, we can say that friction is not a prerequisite for the electrification of bodies. What is the reason that electrification occurs in these cases?
§ 3 The principle of operation of the electrophore machine
The operation of an electrophore machine is based on electrifying the body through influence. An electrified body interacts with any electrically neutral conductor.
When such bodies approach each other due to electric field charged body, a redistribution of charges occurs in the second body. Charges that are opposite in sign to a charged body are located closer to the charged body. Further from the charged body in the conductor (sleeve or cylinder) there are charges of the same name as the charged body.
The distance to the positive and negative charges in the cylinder from the ball is different, therefore the forces of attraction prevail, the cylinder deviates towards the electrified body. If you touch the far side of the body from the charged ball with your hand, the body will jump towards the charged ball. By reducing the repulsive forces, the electrons jump to the hand.
§ 4 Brief summary lesson
Electrification is a phenomenon in which bodies acquire the properties of attracting other bodies.
Electrification can occur in the following ways:
· contact;
·through influence;
upon impact;
·friction.
Substances are: electropositive and electronegative.
You can predict what charges interacting bodies will receive if you know the identity of the substances.
Friction only increases the contact area.
Substances are conductors and dielectrics.
Insulators accumulate charges at points of contact (where they are formed).
Charges in conductors are distributed evenly throughout the entire volume.
List of used literature:
- Peryshkin A.V. Physics 8.- M.: Bustard, 2004.
- Kabardin O.F. Handbook of Physics. - M.: Bustard, 1997.
- Lukashik V.I. Collection of problems in physics. – M.: Yakhont, 2000.
Images used:
As part of today's lesson, we will get acquainted with such a physical quantity as charge, see examples of the transfer of charges from one body to another, learn about the division of charges into two types and the interaction of charged bodies.
Topic: Electromagnetic phenomena
Lesson: Electrification of bodies upon contact. Interaction of charged bodies. Two kinds of charges
This lesson is an introductory one to the new section “Electromagnetic Phenomena”, and in it we will discuss the basic concepts that are associated with it: charge, its types, electrification and the interaction of charged bodies.
The history of the concept of “electricity”
First of all, we should start by discussing the concept of electricity. IN modern world We constantly encounter it at the everyday level and can no longer imagine our life without a computer, TV, refrigerator, electric lighting, etc. All these devices, as far as we know, work thanks to electric current and surround us everywhere. Even technologies that were not initially entirely dependent on electricity, such as the operation of an internal combustion engine in a car, are slowly beginning to fade into history, and their place is being actively taken by electric motors. So where did such a word as “electric” come from?
The word "electric" comes from the Greek word "electron", which means "amber" (fossil resin, Fig. 1). Although we should, of course, immediately stipulate that there is no direct connection between all electrical phenomena and amber, and a little later we will understand where such an association came from among ancient scientists.
First observations electrical phenomena date back to the 5th-6th centuries BC. e. It is believed that Thales of Miletus (ancient Greek philosopher and mathematician from Miletus, Fig. 2) was the first to observe the electrical interaction of bodies. He conducted the following experiment: he rubbed amber with fur, then brought it closer to small bodies (specks of dust, shavings or feathers) and observed that these bodies began to be attracted to the amber for no reason that could be explained at that time. Thales was not the only scientist who subsequently actively conducted electrical experiments with amber, which led to the emergence of the word “electron” and the concept of “electric.”
Rice. 2. Thales of Miletus ()
Let's simulate similar experiments with the electrical interaction of bodies; for this we take finely chopped paper, a glass rod and a sheet of paper. If you rub a glass rod on a sheet of paper and then bring it to finely chopped pieces of paper, you will see the effect of attraction of small pieces to the glass rod (Fig. 3).
An interesting fact is that for the first time such a process was explained quite fully only in the 16th century. Then it became known that there are two types of electricity, and they interact with each other. The concept of electrical interaction appeared in the mid-18th century and is associated with the name of the American scientist Benjamin Franklin (Fig. 4). It was he who first introduced the concept of electric charge.
Rice. 4. Benjamin Franklin ()
Definition.Electric charge - physical quantity, which characterizes the magnitude of the interaction of charged bodies.
What we had the opportunity to observe in the experiment with the attraction of pieces of paper to an electrified stick proves the presence of forces of electrical interaction, and the magnitude of these forces is characterized by such a concept as charge. The fact that the forces of electrical interaction can be different can be easily verified experimentally, for example, by rubbing the same stick with different intensities.
To carry out the next experiment, we will need the same glass rod, a sheet of paper and a paper plume mounted on an iron rod (Fig. 5). If you rub the stick with a sheet of paper and then touch it to the iron rod, you will notice the phenomenon of repulsion of the strips of paper from each other, and if you repeat the rubbing and touching several times, you will see that the effect intensifies. The observed phenomenon is called electrification.
Rice. 5. Paper sultan ()
Definition.Electrification- separation of electrical charges as a result of close contact of two or more bodies.
Electrification can occur in several ways, the first two we looked at today:
Electrification by friction;
Electrifying touch;
Electrification by induction.
Let's consider electrification by induction. To do this, take a ruler and place it on top of the iron rod on which the paper plume is attached, then touch the rod to remove the charge on it, and straighten the stripes of the plume. Then we electrify the glass rod by friction with the paper and bring it to the ruler, the result will be that the ruler will begin to rotate on the top of the iron rod. In this case, you should not touch the ruler with a glass rod. This proves that electrification exists without direct contact between bodies - electrification by induction.
The first studies of the meaning of electric charges date back to a later period in history than the discovery and attempts to describe the electrical interactions of bodies. At the end of the 18th century, scientists came to the conclusion that charge division leads to two fundamentally different results, and it was decided to conditionally divide charges into two types: positive and negative. In order to be able to distinguish between these two types of charges and determine which is positive and which is negative, we agreed to use two basic experiments: if you rub a glass rod on paper (silk), a positive charge is formed on the rod; if you rub an ebonite stick on fur, a negative charge will form on the stick (Fig. 6).
Comment.Ebonite- rubber material with a high sulfur content.
Rice. 6. Electrification of sticks with two types of charges ()
In addition to the fact that the separation of charges into two types was introduced, the rule of their interaction was noticed (Fig. 7):
Like charges repel;
Opposite charges attract.
Rice. 7. Interaction of charges ()
Consider the following experiment for this rule of interaction. Let's electrify a glass rod by friction (i.e., give it a positive charge) and touch it to the rod on which the paper plume is attached, as a result we will see the effect that was already discussed earlier - the stripes of the plume will begin to repel each other. Now we can explain why this phenomenon occurs - since the stripes of the sultan are charged positively (of the same name), they begin to repel as much as possible and form a ball-shaped figure. In addition, to more clearly demonstrate the repulsion of similarly charged bodies, you can bring a glass rod rubbed with paper to an electrified plume, and you will clearly see how the strips of paper will deviate from the rod.
At the same time, two phenomena - the attraction of oppositely charged bodies and the repulsion of similarly charged bodies - can be observed in the following experiment. For it you need to take a glass rod, paper and a foil sleeve secured with a thread on a tripod. If you rub the stick with paper and bring it to an uncharged cartridge case, the cartridge case will first be attracted to the stick, and after touching it will begin to repel. This is explained by the fact that at first the sleeve, until it has a charge, will be attracted to the stick, the stick will transfer part of its charge to it, and the similarly charged sleeve will be repelled from the stick.
Comment. However, the question remains as to why the initially uncharged cartridge case is attracted to the stick. It is difficult to explain this using the knowledge available to us at the current stage of studying school physics, however, let’s try, looking ahead, to do this briefly. Since the sleeve is a conductor, when it finds itself in an external electric field, the phenomenon of charge separation is observed in it. It manifests itself in the fact that free electrons in the sleeve material move in the direction that is closest to the positively charged stick. As a result, the sleeve becomes divided into two conditional areas: one is negatively charged (where there is an excess of electrons), the other is positively charged (where there is a lack of electrons). Since the negative area of the sleeve is located closer to the positively charged stick than its positively charged part, the attraction between the opposite charges will prevail and the sleeve will be attracted to the stick. After this, both bodies will acquire the same charge and repel.
This issue is discussed in more detail in grade 10 in the topic: “Conductors and dielectrics in an external electric field.”
The next lesson will look at the principle of operation of a device such as an electroscope.
Bibliography
- Gendenshtein L. E., Kaidalov A. B., Kozhevnikov V. B. Physics 8 / Ed. Orlova V. A., Roizena I. I. - M.: Mnemosyne.
- Peryshkin A.V. Physics 8. - M.: Bustard, 2010.
- Fadeeva A. A., Zasov A. V., Kiselev D. F. Physics 8. - M.: Education.
- Encyclopedia of Brockhaus F.A. and Efron I.A. ().
- YouTube().
- YouTube().
Homework
- Page 59: Questions No. 1-4. Peryshkin A.V. Physics 8. - M.: Bustard, 2010.
- The metal foil ball was positively charged. It was discharged and the ball became neutral. Can we say that the ball's charge has disappeared?
- In production, air is purified using electrostatic precipitators to capture dust or reduce emissions. In these filters, air passes by oppositely charged metal rods. Why is dust attracted to these rods?
- Is there a way to charge at least part of a body positively or negatively without touching that body with another charged body? Justify your answer.
Physics! What a capacity of words!
Physics is not just sound for us!
Physics - support and basis
All sciences without exception!
- explain to students the mechanism of electrification of bodies,
- develop research and creative skills,
- create conditions for increasing interest in the material being studied,
- help students comprehend the practical significance and usefulness of the acquired knowledge and skills.
Equipment:
- electrophore machine,
- electrometer,
- sultans,
- ebonite and glass rods,
- silk and wool fabrics,
- electroscope,
- connecting wires, distilled water, paraffin balls,
- aluminum and paper cylinders, silk threads (dyed and undyed).
On the desk: Conductors, insulators, resin and glass charges.
- - influence
- - photoelectric effect (under the influence of light).
DURING THE CLASSES
1. introduction teachers
IN Everyday life a person observes a huge number of phenomena and, perhaps, a much larger number of phenomena go unnoticed.
The existence of these phenomena “pushes” a person to search for them, discover and explain these phenomena. Such a phenomenon as bodies falling to the ground no longer causes any surprise in humans. But it should be noted that the earth and this body interact without touching each other. They interact with each other through the most famous action - gravitational attraction (gravitational fields). We are accustomed to the fact that bodies act on each other mainly directly. There are also such phenomena, known to the ancient Greeks, which every time arouse interest among children and adults. These are electrical phenomena.
Examples of electrical interactions are very diverse and are not as familiar to us from childhood as, for example, the gravity of the Earth. This interest is also explained by the fact that here we have great opportunities to create and change experimental conditions using simple equipment.
Let us follow the progress of identifying and studying some phenomena.
2. Historical reference(student reports)
Greek philosopher Thales of Miletus, who lived 624–547. BC, discovered that amber, rubbed on fur, acquires the property of attracting small objects - fluff, straws, etc. This phenomenon was later called electrification.
In 1680, the German scientist Otho von Guericke built the first electric machine and discovered the existence of electrical forces of repulsion and attraction.
The first scientist to argue for the existence of two types of charges was the Frenchman Charles Dufay (1698–1739). Du Fay called the electricity that appears when rubbing resin “resin”, and the electricity that appears when rubbing glass is “glass.” In modern terminology, “resin” electricity corresponds to negative charges, and “glass” electricity corresponds to positive charges. The most convincing opponent of the theory of the existence of two types of charges was the famous American Benjamin Franklin (1706 - 1790). He first introduced the concept of positive and negative charges. He explained the presence of these charges on bodies by an excess or deficiency in the bodies of some general electrical matter. This special matter, later called “Franklin's fluid,” in his opinion, had a positive charge. Thus, when electrified, the body either gains or loses positive charges. It is not difficult to guess that Franklin confused positive charges with negative ones and the bodies exchanged electrons (which carry a negative charge). Largely due to this fact, the direction of movement of the positive charge was subsequently mistakenly taken for the direction of current in metals.
The Englishman Robert Simmer (1707 - 1763) drew attention to the unusual behavior of his wool and silk stockings. He wore two pairs of stockings: black wool for warmth and white silk for beauty. Taking both stockings off his leg at once and pulling one out of the other, he watched as both stockings swelled, taking the shape of his leg and attracting each other. However, stockings of the same color were repelled, and different colors attracted. Based on his observations, Simmer became an ardent supporter of the theory of two charges, for which he was nicknamed the “bloated philosopher.”
To put it simply modern language, his silk stockings had negative charges, and his woolen stockings had positive charges.
3. The phenomenon of electrification of bodies
Teacher: What body is called charged?
Student: If a body can attract or repel other bodies, then it has an electric charge. Such a body is said to be charged. Charge is a property of bodies, the ability for electromagnetic interaction.
(Demonstration of the action of a charged body).
Teacher: What is an electroscope?
Student: A device that allows you to detect the presence of a charge in a body and evaluate it is called an electroscope.
Teacher: How does an electroscope work and work?
Student: The main part of the electroscope is a conductive insulated rod on which a needle is attached and can rotate freely. When a charge appears, the arrow and the rod are charged with charges of the same sign and therefore, repelling, they create a deflection angle, the value of which is proportional to the charge received.
(Demonstration of the operation of the device).
Teacher: Electrification of bodies can occur in various cases, i.e. There are different ways to electrify bodies:
- friction,
- blow,
- by contact,
- influence,
- under the influence of light energy.
Let's look at some of them.
Student: If rub an ebonite stick on wool, then the ebonite will receive a negative charge, and the wool will receive a positive charge. The presence of these charges is detected using an electroscope. To do this, touch the electroscope rod with an ebonite stick or woolen rag. In this case, part of the charge of the test body passes to the rod. By the way, in this case a short-term electric current occurs. Let us consider the interaction of two paper cartridges suspended on a thread, one charged from an ebonite stick, the other from a woolen rag. Note that they are attracted to each other. This means that bodies with opposite charges attract. Not every substance can transmit electrical charges. Substances through which charges can be transferred are called conductors, and substances through which charges cannot be transferred are called non-conductors - dielectrics (insulators). This can also be determined using an electroscope, connecting it to a charged body and substances of various kinds.
White silk thread does not conduct a charge, but dyed silk thread does. (Fig. A)
White silk thread Dyed silk thread
Separation of charges and the appearance of a double electrical layer at the points of their contact, any two different bodies, insulators or conductors, solids, liquids or gases. When describing electrification by friction, we always took only good insulators for the experiment - amber, glass, silk, ebonite. Why? Because in insulators the charge remains in the place where it originated and cannot pass through the entire surface of the body to other bodies in contact with it. The experiment fails if both rubbing bodies are metals with isolated handles, since we cannot separate them from each other over the entire surface at once.
Due to the inevitable roughness of the surface of the bodies, at the moment of separation there are always some last points of contact - “bridges”, through which at the last moment all excess electrons escape and both metals turn out to be uncharged.
Teacher: Now let's consider electrification by contact.
Student: If we immerse a paraffin ball in distilled water and then remove it from the water, both the paraffin and the water will be charged. (Fig.B)
The electrification of water and paraffin occurred without any friction. Why? It turns out that during electrification by friction we only increase the area of contact and reduce the distance between the atoms of the rubbing bodies. In the case of water - paraffin, any roughness does not interfere with the approach of their atoms.
This means that friction is not a prerequisite for the electrification of bodies. There is another reason why electrification occurs in these cases.
Student: The operation of the electrophore machine is based on the electrification of the body through influence. An electrified body can interact with any electrically neutral conductor. When these bodies come together, due to the electric field of the charged body, a redistribution of charges occurs in the second body. Closer to the charged body there are charges opposite in sign to the charged body. Further from the charged body in the conductor (sleeve or cylinder) there are charges of the same name as the charged body.
Since the distance to the positive and negative charges in the cylinder from the ball is different, the forces of attraction prevail and the cylinder deviates towards the electrified body. If you touch the far side of the body from the charged ball with your hand, then the body will jump towards the charged ball. This occurs because electrons jump to the hand, thereby reducing the repulsive forces. Rice. D.
Teacher: How long will this situation last? (Fig.D)
Student: After a few seconds, the charges will divide and the cylinder will come off the ball. Their character will further depend on the value of the sum of their charges. If their sum is zero, then their interaction forces are zero. If Fp< 0, то они оттолкнутся друг от друга, но на меньший угол .
Teacher: Let's consider the electrification of bodies under the influence of light energy (photoelectric effect).
Student: Let's direct a strong light beam to a zinc disk (plate) attached to an electrometer. Under the influence of light energy, a certain number of electrons fly out of the plate. The plate itself turns out to be positively charged. The magnitude of this charge can be judged by the angle of deflection of the electrometer needle. (Fig. E)
Teacher: We are convinced that when the distance between atoms decreases, the phenomenon of electrification occurs more efficiently. Why?
Student: Because this increases the Coulomb forces of attraction between the nucleus of an atom and the electron of a neighboring atom.
The electron that is weakly bound to its nucleus jumps over.
Teacher: Let's look at how the chemical elements are arranged in the periodic table chemical elements.
Student: There are about 500 forms of the Periodic Table of chemical elements. Of these, in one, 18-cell, the elements are placed according to the structure of the electronic shells of their atoms and is given in the reference book on general and inorganic chemistry by N.F. Stas.
The properties and characteristics of atoms are consistent with the periodic law, including the electronegativity and valence of elements.
The radii of atoms and ions decrease in periods, because the electron shell of an atom or ion of each subsequent element in a period becomes denser compared to the previous one due to an increase in the charge of the nucleus and an increase in the attraction of electrons to the nucleus.
The radii in groups increase because the atom (ion) of each element differs from its superior one by the appearance of a new electronic layer. When an atom transforms into a cation (positive ion), the atomic radii decrease sharply, and when an atom transforms into an anion (negative ion), the atomic radii remain almost unchanged.
The energy expended to remove an electron from an atom and become a positive ion is called ionization. The voltage at which ionization occurs is called ionization potential.
Ionization potential is a physical characteristic that is an indicator of the metallic properties of an element: the lower it is, the easier it is for an electron to detach from an atom and the more pronounced the metallic (reducing) properties of the element are.
Table 1. Ionization potentials of atoms (eV/atom) of elements of the second period
| Element | J 1 | J2 | J 3 | J 4 | J5 | J 6 | J 7 | J 8 |
| Lithium | 5,39 | 75,6 | 122,4 | --- | --- | --- | --- | --- |
| Beryllium | 9,32 | 18,2 | 158,3 | 217,7 | --- | --- | --- | --- |
| Bor | 8,30 | 25,1 | 37,9 | 259,3 | 340,1 | --- | --- | --- |
| Carbon | 11,26 | 24,4 | 47,9 | 64,5 | 392,0 | 489,8 | --- | --- |
| Nitrogen | 14,53 | 29,6 | 47,5 | 77,4 | 97,9 | 551,9 | 666,8 | --- |
| Oxygen | 13,60 | 35,1 | 54,9 | 77,4 | 113,9 | 138,1 | 739,1 | 871,1 |
| Fluorine | 17,40 | 35,0 | 62,7 | 87,2 | 114,2 | 157,1 | 185,1 | 953,6 |
| Neon | 21,60 | 41,1 | 63,0 | 97,0 | 126,3 | 157,9 |
Teacher: There is such a thing as electronegativity, which plays a decisive role in the electrification of bodies. The sign of the charge received by the element during electrification depends on it. Electronegativity - what is it?
Student: Electronegativity is the property of a chemical element to attract electrons to its atom from atoms of other elements with which the element forms chemical bonds in compounds.
The electronegativity of elements was determined by many scientists: Pauling, Allred and Rochow. They concluded that the electronegativity of elements increases in periods and decreases in groups, similar to ionization potentials. The lower the ionization potential value, the greater the probability of losing an electron and becoming a positive ion or a positively charged body if the body is homogeneous.
Table 2. Relative electronegativity (EO) of elements of the first, second and third periods.
| Element | EO | Element | EO | Element | EO | |||
| According to Pauling | According to Allred-Rochow | According to Pauling | According to Allred-Rochow | According to Pauling | According to Allred-Rochow | |||
| H | 2,1 | 2,20 | Li | 1,0 | 0,97 | Na | 0,9 | 1,01 |
| Be | 1,5 | 1,17 | Mg | 1,2 | 1,23 | |||
| B | 2,0 | 2,07 | Al | 1,5 | 1,47 | |||
| C | 2,5 | 2,50 | Si | 1,8 | 1,74 | |||
| N | 3,0 | 3,07 | P | 2,1 | 2,06 | |||
| O | 3,5 | 3,50 | S | 2,5 | 2,44 | |||
| F | 4,0 | 4,10 | Cl | 3,0 | 2,83 | |||
Teacher: From all this we can draw the following conclusion: if two homogeneous elements from the same period interact, then we can tell in advance which of them will be positively charged and which negatively.
A substance whose atom has a higher valency (higher group number) relative to the atom of another substance will be negatively charged, and the second substance will be positively charged.
If homogeneous substances from the same group interact, then the substance with a lower number of the period or series will be negatively charged, and the second interacting body will be positively charged.
Teacher: In this lesson we tried to reveal the mechanism of electrification of bodies. We found out why the body, after electrification, receives a charge of one or another sign, i.e. answered the main question - why? (as, for example, the mechanics section “Dynamics” answers the question: why?)
Now let's list the positive and negative values of the electrification of bodies.
Student: Static electricity may have Negative influence:
Attraction of hair to the comb;
Pushing hairs away from each other, like a charged plume;
Sticking of various small objects to clothing;
In weaving factories, threads stick to bobbins, which leads to frequent breaks.
Accumulated charges can cause electrical discharges, which can have various consequences:
Lightning (leads to fires);
A discharge in a fuel tanker will cause an explosion;
When filling with a flammable mixture, any discharge can lead to an explosion.
To remove static electricity, all devices and equipment, and even the fuel truck, are grounded. A special antistatic substance is used.
Student: Static electricity can be beneficial:
When painting small parts with a spray gun, the paint and body are charged with opposite charges, which leads to great savings in paint;
For medicinal purposes, a static shower is used;
Electrostatic filters are used to clean the air from dust, soot, acid and alkaline vapors;
For smoking fish in special electrometers (the fish is charged positively, and the electrodes are negatively charged, smoking in an electric field occurs tens of times faster).
Summing up the lesson.
Teacher: Let's remember the purpose of our lesson and draw brief conclusions.
- What was new in the lesson?
- What was interesting?
- What was important in the lesson?
Student conclusions:
- Phenomena in which bodies acquire the ability to attract other bodies are called electrification.
- Electrification can occur by contact, through influence, or by irradiation with light.
- Substances can be either electronegative or electropositive.
- Knowing the identity of the substances, it is possible to predict what charges the interacting bodies will receive.
- Friction only increases the contact area.
- Substances are conductors and non-conductors of electricity.
- Insulators accumulate charges where they are formed (at points of contact).
- In conductors, charges are distributed evenly throughout the volume.
Discussion and grading of lesson participants.
Literature.
- G.S. Landsberg. Elementary physics textbook. T.2. – M., 1973.
- N.F. Stas. Handbook of general and inorganic chemistry.
- I.G.Kirillova. Physics reading book. M., 1986.