Electric charge conservation law. Electrification of tel. Two kinds of charges. Law of Conservation of Electric Charge Improvement of Electrostatic Machines

Electricity obtained by friction on a particular body turns out to be unequal in its properties.

Let's do the following experiment. Using a silk thread, we hang a light cork or elderberry ball on a stand and then, electrifying an ebonite stick by rubbing it against fur or cloth, bring it to the cork ball. In this case, the following will happen: the ball will first quickly be attracted to the ebonite stick (Fig. 2), but as soon as it touches it, it will immediately push off and take the position shown in Fig. 2. 3. If a glass rod, electrified by friction against silk or leather, is brought to this charged ball, the ball will be attracted to it.

Rice. 2. Attracting a cork ball to an electrified rod

Rice. 3. Repulsion of the cork ball, which received a charge from an electrified rod

Let us now take two balls, suspended from two posts on silk threads, and touch each of them with an electrified glass rod.

After that, bringing both balls closer to one another, we note that they will tend to push off and take the position shown in Fig. 4. The same will happen if both balls are charged with an electrified ebony stick.

Rice. 4. Balls with the same charges repel

Quite different properties will be found if the first of the two balls is charged by touching it with an electrified glass rod, and the other ball is electrified with an ebonite rod. The balls will be attracted to one another (Fig. 5).

Rice. 5. Balls with opposite charges attract

The experiments carried out show that it is necessary to distinguish between two electrical states of bodies, or, as they say, two types of electricity:

1) electricity obtained on glass by rubbing it against silk fabric or leather, which they agreed to call positive electricity;

2) electricity obtained on ebonite by rubbing it against fur or woolen fabric, which they agreed to call negative electricity.

Positive electricity is usually denoted by the plus sign (+), and negative by the minus sign (-).

Bodies, electrified with electricity of the same name, no matter whether positive or negative, repel one another (Fig. 4). Bodies, electrified by opposite electricity, are attracted to one another (Fig. 5).

It should be borne in mind that the attraction or repulsion of the electrified balls will be the stronger, the smaller the distance between them and the greater in magnitude the charge imparted to each of the balls.

It should also be remembered that if we rub the glass rod with silk and receive positive electricity on the glass rod, then, in turn, we receive negative electricity in the same amount on the silk. And, conversely, when ebonite rub against fur on ebony, we get negative electricity, and the fur itself is electrified positively.

Gray made another very important discovery, the significance of which was understood later. Everyone knew that if you touch an electrified glass rod with an insulated metal cylinder, electricity will also go to the cylinder. However, it turned out that it is possible to electrify the cylinder without touching the glass rod, but only by bringing it closer to it. As long as the cylinder is near the electrified rod, electricity is found on it.

Gray's published experiments aroused the interest of the French physicist Charles François Dufay (1698–1739) and prompted him to begin experiments in the study of electricity. Experiments with the first electric pendulum, i.e. with a wooden ball suspended on a thin silk thread (Fig. 5.2), carried out around 1730, showed that such a ball is attracted by a rubbed stick of sealing wax. But as soon as you touch it, the ball immediately repels itself from the wax stick, as if avoiding it. If you now bring a glass tube, rubbed against the amalgamated skin, to the ball, the ball will be attracted to the glass tube and repelled by the wax stick. This difference, first noted by Charles Dufay, led him to the discovery that electrified bodies attract non-electrified ones, and as soon as the latter are electrified by touch, they begin to repel each other. He establishes the existence of two opposite kinds of electricity, which he calls glass and resin electricity. He also notes that the former is found on glass, precious stones, hair, wool, etc., while the latter appears on amber, resin, silk, etc. Further research showed that all bodies were electrified, either like glass rubbed against skin or resin rubbed against fur. Consequently, there are two types of electric charges, and homogeneous charges are repelled from each other, and dissimilar ones are attracted. Electric interaction forces

charges, manifested in attraction or repulsion, are called electric. That is, electric forces are created by electric charges and act on charged bodies or particles.

An excess of charges of any one type in a given body is called the amount of its charge, or, in other words, the amount of electricity (q).

Charles Dufay was the first scientist to extract electrical sparks from an electrified human body on an insulated stand. This experience was so new and original at the time that Abbot Jean Nollet (1700–1770), who also studied electrical phenomena, was horrified when he first saw it.

The outstanding American physicist Benjamin Franklin gave a very successful designation of the two kinds of electricity, which has survived to our time.

"Tar" electricity was called negative by Franklin, and "glass" - positive. He chose these names because "resinous" and "glassy" electricity, like positive and negative values, mutually annihilate.

The phenomena of electrification are explained by the peculiarities of the structure of atoms and molecules of various substances. After all, all bodies are built of atoms. Each atom consists of a positively charged atomic nucleus and negatively charged particles - electrons moving around it. Atomic nuclei of various chemical elements are not the same, but differ in the amount of charge and mass. Electrons are all completely identical, but their number and location in different atoms are different.

To get an idea of ​​the magnitude of a charge in 1 C, we calculate the force of interaction of two charges, one coulomb each, placed in a vacuum at a distance of 1 m from each other. Using the formula of Coulomb's law, we get that F = 9 · 10 9 N, or approximately 900,000 tons. Thus, 1 C is a very large charge. In practice, such charges do not occur.

With their help, Coulomb determined that two small electrified balls exert on each other in the direction of their connection line, depending on whether they are electrified with the same or opposite name, an attractive or repulsive interaction force F, equal to the product of their point electric charges (respectively q 1 and q 2) divided by the square of the distance r between them. That is

Charles Augustin de Coulomb (1736-1806) - French physicist and engineer - designed a torsion balance to measure the force of magnetic and electrical attraction.

In the normal state of an atom, the positive charge of its nucleus is equal to the total negative charge of the electrons of this atom, so that any atom in the normal state is electrically neutral. But under the influence of external influences, atoms can lose part of their electrons, while the charge of their nuclei remains unchanged. In this case, the atoms are charged positively and are called positive ions. Atoms can also attach additional electrons to themselves and become negatively charged. Such atoms are called negative ions.

The law, according to which two electrified bodies act on each other, was first formulated in 1785 by Charles Coulomb in an experiment with a device, which he called a torsion balance (Fig. 5.3).

F = (q 1 q 2) / 4 π ε а r 2,

where ε a is the absolute dielectric constant of the medium in which the charges are located; r is the distance between charges.

This conclusion is called Coulomb's law. Subsequently, a unit was named after Coulomb the amount of electricity used in electrical engineering.

In the SI system, one coulomb (1 C) is taken as a unit of electricity - a charge flowing through the cross section of a conductor in one second at a current of one ampere.

Purpose of the work: acquaintance with the history of the development of electrical engineering, with the creative way of the most prominent scientists who contributed to the study of electrical and magnetic phenomena, identifying their patterns, creating electrical devices.

Completion of work

7. Discovery of the phenomenon

3. Development of electrostatics of electrostatic induction. Study of electrification processes

8. Interaction research

4. Invention of the Leyden bank of charged bodies. Discovery of Coulomb's Law

The first observations of magnetic and electrical phenomena date back to ancient times. The mysterious ability of a magnet to attract iron objects is mentioned in ancient chronicles and legends that have come down to us from Asia (India and China), Ancient Greece and Rome.

A very figurative explanation of the properties of a magnet is given in the famous poem "On the Nature of Things" by the Roman poet Lucretius (99-55 BC), written more than 2 thousand years ago.

From ancient legends and chronicles dating back to the second millennium BC, we learn about many interesting facts practical use of the magnet. The ancient Indians used a magnet to extract iron arrowheads from the bodies of wounded soldiers. The Chinese chronicles tell of a magical magnetic gate through which a man who hid a metal weapon could not pass. During excavations of the Olmec settlement (Central America), sculptures of three thousand years ago were found, carved from magnetic blocks.

In China in the second millennium BC. the first compasses of various designs were already in use. In one of the museums, there is a Chinese compass from a thousand years ago, reminiscent of a spoon.

Naturally, ancient scientists and

Naturalists have pondered the reason for the mysterious properties of the magnet in the Chinese compass. Plato, for example,

explained them by their divine origin.

First observations of magnetic and electrical phenomena

WITH the name of one of the ancient sages - Thales(640-550 BC) legends that have come down to us are connected

O the property of rubbed amber to attract the lungs of the body. In his opinion, in amber, as in a magnet, there is a soul, which is the primary cause of attraction.

Products made of amber, shiny and beautiful, were widely used by ancient people for decoration, so it is likely that many could notice that rubbed amber attracts light straws, pieces of fabric, etc.

The Greeks called amber "electron". From this, many centuries later, the word "electricity" came from. It is known that one of the ancient Greek writings described a stone (apparently precious), which, like amber, was electrified by friction. But the ancient Greeks probably did not know about the electrification of other bodies.

And one more curious phenomenon did not go unnoticed by the ancient peoples who lived on the Mediterranean coast and in the basin of the river. Nile. We are talking about "electric" fish - stingray and catfish. The Greeks called them "nare", which means "paralyzing". When in contact with these fish, which have electrical organs, a person experienced strong shocks. It is known that in the 1st century A.D. Roman doctors used the electric ray to treat gout, headaches, and other ailments.

And, of course, the ancient peoples watched formidable peals of thunder and bright flashes of lightning, which inspired them with natural fear, but none of the wise men of those times could have thought that the attraction of rubbed amber, and the blows of electric fish, and the phenomenon of thunderstorms in the atmosphere are of the same nature.

The decline of ancient culture was noticeably reflected in the study of electrical and magnetic phenomena. From numerous sources it follows that practically until 1600, not a single discovery was made in the field of electrical phenomena, and in the field of magnetism, only the ways of using the compass by navigators (by the Arabs in the 9th century, and by the Europeans in the 11th century) were described.

In the XIII century. scientists managed to establish a number of properties of a magnet: the existence of opposite poles and their interaction; propagation of magnetic action through various bodies (paper, wood, etc.); methods of making magnetic arrows were described, and the French scientist Pierre Peregrine (1541-1616) first equipped the compass with a graduated scale.

In the XIII-XIV centuries. Catholic captains used the compass in secret, fearing to be caught by the fire of the Inquisition, which saw in the compass a devilish instrument created by sorcerers.

For many centuries, magnetic phenomena were explained by the action of a special magnetic fluid, and as will be shown below, only the outstanding French physicist A.M. Ampere in the 20s of the XIX century. first explained the electrical nature of magnetism.

Experimental research by W. Hilbert

A significant breakthrough in the concept of electrical and magnetic phenomena came at the very beginning of the 17th century, when the fundamental scientific work of a prominent English scientist (physician to Queen Elizabeth of England) was published William Gilbert(1554-1603) "On the magnet, magnetic bodies and the big magnet - the Earth" (1600). As a follower of the experimental method in natural science, W. Hilbert conducted more than 600 skillful experiments, which, as he wrote, discovered the secrets of the "hidden causes of various phenomena."

Unlike many of his predecessors, W. Hilbert believed that the magnetic needle moves under the influence of the magnetism of the Earth, which is a large magnet. He based his conclusions on an original experiment, which he carried out for the first time. He made a small ball out of magnetic iron ore - "the little Earth - terella" and proved that the magnetic needle takes on the same positions in relation to the surface of this "terella" as it takes in the field of terrestrial magnetism. He established the possibility of magnetizing iron by means of terrestrial magnetism.

Investigating magnetism, W. Hilbert also took up the study of electrical phenomena. He proved that not only amber has electrical properties, but also many other bodies: diamond, sulfur, resin, rock crystal.

Electrifying when rubbed. He called these bodies "electrical" in accordance with the Greek name for amber (electron). But W. Hilbert unsuccessfully tried to electrify metals without insulating them, and therefore came to the erroneous conclusion that it was impossible to electrify metals by friction. This conclusion of W. Hilbert was convincingly refuted two centuries later by the outstanding Russian electrical engineer, academician Vasily Vladimirovich Petrov.

W. Hilbert correctly established that the "degree of electrical force" is different, and moisture reduces the electrification of bodies when rubbed. Comparing magnetic and electrical phenomena, W. Hilbert argued that they have a different nature: for example, "electrical force" comes only from friction, while the magnetic one constantly acts on iron; a magnet lifts bodies of considerable weight, electricity only light bodies. This erroneous conclusion of W. Hilbert held out in science for over 200 years.

The idea that electrical phenomena are due to the presence of a special "electric fluid", analogous to the "heat source" and "light emission."

The fundamental work of B, Hilbert survived during the 17th century. several editions, it was the reference book of many naturalists in different countries Europe and played a huge role in the development of the theory of electricity and magnetism. The great G. Galileo wrote about the writings of W. Hilbert: "I give the greatest praise and envy this author."

O. Guericke's electrostatic machine

One of the first who, having become acquainted with the book of W. Hilbert, decided to obtain stronger manifestations of electrical forces, was the Magdeburg burgomaster Otto von Guericke (1602-1686).

In 1650, he made a ball of sulfur the size of a child's head, planted it on an iron axle mounted on a wooden tripod. With the help of the handle, the ball could be rotated and rubbed with the palms of the hands or with a piece of cloth pressed against the ball by the hand. It was the first simplest electrostatic machine.

O. Guericke managed to notice a faint glow of an electrified ball in the dark and, what is especially important, for the first time to discover that the fluffs attracted by the ball, after a while, repel from it. This phenomenon is not O. Guericke. nor many of his contemporaries could explain for a long time.

German scientist G.V. Leibniz (1646-1716), using O. Gericke's machine, observed an electric spark - this is the first mention of this mysterious phenomenon.

Improvement of electrostatic machines

During the first half of XVII v. the electrostatic machine underwent a number of improvements: the sulfur ball was replaced by a glass one (since the glass was more intensely electrified), and later instead of balls or cylinders (which were more difficult to manufacture, and when heated, they often exploded) glass discs began to be used. For rubbing, leather pads were used, pressed against the glass with springs; later, to increase the electrification, the pads were covered with amalgam.

An important new design element of the machine was the conductor (1744) - a metal tube suspended on silk threads, and later installed on insulated supports. The conductor served as a reservoir for collecting electrical charges generated by friction. After the invention of the Leyden jar, it was also installed next to the machine.

Electrostatic machine. End of the 18th century Unknown master.

Instrumental Chamber of the St. Petersburg Academy of Sciences

Two kinds of electricity are revealed and the laws of their interaction are established. The conductive and insulating properties of the materials have been found.

Experiments on the transfer of electric charge. Discovery of electrical conductivity

A significant step in the study of the properties of electric charges was the research of a member of the English Royal Society Stephen Gray (1670-1736) and a member Paris Academy sciences Charles Francois Dufay(1698 -1736).

As a result of numerous experiments, S. Gray was able to establish that the electrical ability of a glass tube to attract light bodies can be transferred to other bodies, and he showed (1729) that bodies, depending on their relationship to electricity, can be divided into two groups: conductors ( e.g. metallic thread, wire) and non-conductors (e.g. silk thread).

Continuing the experiments of S. Gray, Sh.F. Du Fay (in 1733) discovered two kinds of electric charges - "glass" and "resin" and their peculiarity to repel the same charges and attract opposite charges.

Du Fay also created a prototype electroscope in the form of two suspended and diverging during electrification.

By the end of the 30s of the XVIII century. were successfully used as conductors: linen thread (Guericke, 1663), hemp twine, undried wood, metal wire (Gray, 1729), wet catgut (Desagulier,

1738); as non-conductors: silk (Wheeler in the experiment made by Gray, 1729), horsehair (Gray, 1729), glass and sealing wax (Du Fay, 1733). The length of the electric lines reached several hundred meters.

O. Guericke, conducting experiments with an electrostatic machine, discovered that a sulfur ball rubbed with his hands transfers its ability to attract light bodies to an elbow-long linen thread, the end of which, hooked onto a stick, is located at the very ball; the attraction was observed within more than an inch from the lower end of the thread.

Using a glass tube (or stick), Stephen Gray repeated Guericke's experiment. In 1729, Gray discovered a series of bodies to which a tube could impart "electrical force." These are wooden rods and wires (iron and brass), which Gray inserted into the tube (through the cork), hemp twine, which he tied to the tube or pushed into it. The maximum length of a room power transmission over twine or wire hanging from a tube did not exceed 1 m, and the maximum length of a horizontal room power transmission over joined wooden conductors was no more than 5.5 m, including the length of the tube. Gray checked the message to the bodies of "electric force" with the help of a fluff, which could be attracted to the body, push off from it, hover

in the air.

Gray decided to try to transmit electricity horizontally in order to figure out the question that was preoccupying him, how far can electricity be transmitted. To do this, he hung the string on nails driven into a wooden beam at the same height. The experience did not work out. Gray made the correct conclusion that the electricity went into the beam.

The difficulty was overcome thanks to Wheeler's brilliant idea, with which Gray experimented in the summer of 1729. Priest Granville Wheeler (d. 1770) proposed to support the line of communication (according to Gray) with a silk cord, rather than hang it on nails driven into a beam ... The first experience exceeded all expectations. The electricity was transmitted over a line about 25 meters long. By replacing the silk cord with metal wire, Gray again received a negative result.

Gray "... showed that electricity can be transmitted without touching the transmission line with the tube, but only by holding the tube close to the line," that is, in later terminology, by means of electrostatic induction.

1

Lesson topic: Electrification of bodies. Two kinds of electric charges

(8th grade)

The purpose of the lesson:

to acquaint students with the history of the origin of the doctrine of electricity, introduce the concept of "Electric charge", "electrification, teach how to detect electric charges on bodies rubbed against each other and prove that there are two kinds of charges; continue the formation of skills to work with devices and equipment.

Demonstrations:

electrification of bodies, 2 kinds of electric charges, presentation made using computer disks “Electronic lessons and tests. Electric fields "," Physicon. Library of visual aids ", etc.

During the classes.

Brief analysis mistakes made in the control work on the topic "Thermal phenomena", recommendations for their elimination.

Learning new material.

Before announcing the topic of our today's lesson, I want to voice the following situations and ask you at the end of the lesson to answer the questions, are there any common patterns between them, how appropriate are they in today's lesson?

(Situations are projected onto the screen

Lightning flashed between the clouds.

General cleaning in the kitchen was in full swing. After cleaning the floor, Sherlock Holmes took up the furniture. He vigorously wiped the polished surface of the kitchen cabinets with a dry synthetic cloth, and the oily surfaces with damp. The result exceeded all expectations. The kitchen shone with perfect cleanliness.

Note from the newspaper. “It was already past midnight when A. Tretyakov, a worker of the Bryansk oil depot, having filled 8 tanks with aviation gasoline, transferred the filling hose to another empty container. As soon as the hose touched the neck of the cistern, a 15-meter high orange-bright column of fire shot up high up. Tretyakov was thrown far from the tank by a powerful blast wave. The explosion occurred due to non-observance of labor safety "

Supposed answer: we are talking about electrical phenomena. After all, lightning is email. phenomenon. So the rest?

2

Yes, indeed today in the lesson we will talk about very interesting phenomena. In general, the word “electricity has become part of our everyday life. Have

every house has a variety of household e-mails. devices. Electricity is indispensable neither in transport, nor in agriculture, nor in everyday life, etc.

The topic of today's lesson is: electrification of bodies. Electric charge. 2 kinds El. charges. (single-root words)

Work plan

Find out: 1. The origin of the terms "electricity, electric charge"

2. How to electrify tel. What are the 2 kinds of electric charges? How do electrified bodies interact? How to detect if a body is electrified or not?

3. Carry out experiments on electrification, explain the observed phenomena.

4. The practical importance of electrification.

Problem experiment on electrification of bodies.

A wooden ruler is attached to the water bottle. We bring an ebony stick, rubbed against the wool. (The ruler starts to move).

We replace the ruler with met. foil folded several. times. (The foil starts to move).

Charging. pieces of paper from an electrified stick (glass and ebonite), "raise the little men."

The phenomenon that we have just observed (the ability of bodies to attract other bodies, after they have been rubbed), called. electrification bodies, or they say thatthey are given an electric charge. This electrification is also called. static electricity.

Have you ever observed such phenomena?

The ability of bodies after rubbing (by the way, not necessarily friction, it is enough to simply bring the body into contact or even subject it to deformation) to attract small objects and not only (the ruler is large, and the pieces of paper are small) was known in the 6th century BC.

Greek philosopherThales of Miletus found that amber, rubbed against fur, acquires the properties of attracting fluffs, straws,

(The student tells)

Legend has it that Thales' daughter spun wool with an amber spindle. Having dropped it once into the water, she began to wipe the spindle with a woolen tunic and noticed that several villi had stuck to the spindle, and the more she wiped the spindle, the more the villi adhered. The girl told her father that he did not hesitate to experiment with various amber products and found that they all behaved the same after rubbing.

3

It is from the word amber that the word "electricity

Have The first scientific concepts of electricity were set forth by the court physician in England. Queen ElizabethWilliam Hilbert (1544-1603 )(TO),

who proved that grated amber has the ability: not only glass, sealing wax, sulfur, and they attract not only straws, but also metals, wood, leaves, pebbles, lumps of earth and even water. At home, you can conduct such an experiment ... (the attraction of a stream of water to an electrified stick).

Q. How many bodies are involved in electrification?

1 experiment .

Place a strip of polyethylene on a strip of paper. Pressing with the back of your hand, iron them. Then we spread it to the sides and slowly bring it together. What is being observed ?. The stripes are attracted to each other. Take 2 pieces of fluffed cotton wool, bring it to the paper strip and immediately to the film. The fluff is attracted to both paper and film.

experiment with a sleeve made of staniol. (She is attracted to both the glass stick, rubbed against the paper, and to the sheet of paper.).

experiment a glass rod, rubbed against a sheet of rubber, attracts light papers and rubber too. Conclusion, in the process of electrification, 2 bodies are involved and 2 bodies are electrified.

Experiments on the existence of two kinds of electric charges.

A casing made of staniol is suspended on a silk thread.

1 Let us bring a glass stick, rubbed against silk or paper, to it (first the sleeve touches, and then repels from the stick)

2. Let's bring to it an ebony stick, worn on wool

3. Let's bring a glass rod, rubbed against the rubber

4. Experience in the electrification of two sultans with pom. electroph. cars.(TO)

5. Experience with "floating cotton wool" or its movement in the field El. cars.

Fr. The physicist Charles Dufay studied the interaction of electrified bodies in 1730. He noticed that in some cases such bodies are attracted to a resin stick, and in another case they repel each other, for example, two glass sticks, rubbed against silk, repel each other, but are attracted to an ebony stick, rubbed against wool .. He explained this by the fact that there are 2 kinds of electricity "glass" and

"Resinous". Bodies charged with electricity of the same kind repel, and opposite ones attract. In 1778, an American physicist and

4 politician Benjamin Franklin called "glass electricity" positive and "tar" negative

Experiment.

Before conducting it, briefly tell about the design of the electrometer, and the contribution of Richman.

Rub the ebony stick on the cloth and, wrapping it with cloth, put it inside the hollow ball of the electrometer. They took the stick out of the cloth, while the arrow deviates. Why?

Insert the stick inside the felt, the arrow returns to the zero position.

Conclusion. The charges do not arise and do not disappear, but only separate, while on both bodies in contact during friction, the modes are equal. , but charges of opposite sign.

Primary anchoring

"Weak link"

1. These phenomena were observed in antiquity.

2. Electron translated from Greek.

3. Are one or two bodies electrified by friction?

4 What are the 2 kinds of email. charges n. in nature?

5. Who coined the terms "glass and resin" electricity?

6.How to electrify a glass bottle and a flap of skin with charges of different signs, having these 2 objects in your hands?

7. How do 2 ebony sticks, electrified by friction on the fur, interact with each other?

8. When painting with a spray gun, metal. the surface is given a charge of the same kind, and the paint droplets are given a charge of the opposite sign. Why do you need to do this? (The paint lays down evenly).

9. It is commonly said that hair that is electrified when combed is attracted to the comb. Would it be correct to say "The comb is attracted by the hair?" (Yes, because the action is not one-sided).

( an application separately, at the discretion of the teacher, for example, an explanation of the observed phenomena, the manufacture of a device for recording the presence of electrification of bodies)

During the group report

explanation of the observed phenomena:

1.When pumping air through the cut. the tube is electrified rubber and moving air. I ask the question, what if the fuel is supplied through the hose? You can start talking about the third situation (Tretyakov).

5 2.With friction of dry sand, the cavity of the ball is electrified, the electrometer fixes the email. charge.

3. Etc.

Then demonstrated video clip "Thunderstorm",

after which the contribution to the study of the atmosphere is reported. e-mail the phenomena of M.V. Lomonosov and Academician of the Petersburg Academy of Sciences, friend of M.V. Lomonosov, Georg Richman.

Returning to the second situation.

When rubbed with a synthetic cloth, polished surfaces become electrified and acquire an electric charge along with the dust on them; in this case, the fabric also receives an electric charge, but of a different sign .. As a result, dust and fabric are attracted to each other, and the dust densely settles on the rag .. Surfaces painted with oil paint do not electrify during friction, so dust is removed from them with a damp rag, which wets dust, causing it to stick to the fabric.

Verification test work. (Attached separately at the discretion of the teacher).

(Cross-check by answers on the back of the board)

Summing up the results of the work.

House. Exercise :

Do an experiment and explain it.

Take a thick sheet from org. glass .. Rub it thoroughly with a piece of newspaper .. Take the ball from table tennis... Place it in the middle of the sheet. Place your palms at the edge of the glass and slowly bring them closer to the ball. Explain the observed phenomena.

Use an old plastic soap dish to make a "vacuum cleaner".

p. 25.26.

"Detective" Can 2 similarly charged bodies attract?

Mini-essay "Is electrification useful or harmful?"

Lesson objectives:

educational:

• the formation of initial ideas about an electric charge, about the interaction of charged bodies, about the existence of two types of electric charges.
• clarification of the essence of the process of electrification of bodies.
• determination of the sign of the charge of an electrified body.

developing:

• development of skills to highlight electrical phenomena in nature and technology.
• acquaintance with brief historical information on the study of electric charges.

educational:

• developing the ability to work in a team,
• education of curiosity.

Equipment: an electroscope, electrometers, a foil sleeve on a support, glass and ebonite sticks, a piece of fur and a crack, polyethylene, paper, TV, VCR.

Lesson plan

1. Organizing time.
2. Homework record: § 25, 26, 27. Fill in the table.
3. Explanation of the new material:
4. Primary control.
5. Consolidation of the studied material.
6. Summarizing. Grading.

During the classes

"Find the beginning of everything and you will understand a lot." (Kozma Prutkov.)

Student 1: Imagine a scene like this:

In ancient Greece, in the beautiful city of Miletus, the philosopher Thales lived. And then one evening his beloved daughter comes up to him. Explain why my threads get tangled when I work with an amber spindle, dust and straws stick to the yarn. It is very uncomfortable.

Thales takes a spindle, rubs it and sees small sparks.

2 student: They say the truth: “The thunder will not break out - the man will not cross himself”. And what is thunder without lightning? How many million times should lightning flash for a peasant, crossing himself, to finally think: what is it?

Teacher: It would seem that there is nothing in common between a rubbed amber spindle that attracts objects and lightning. But all these are ELECTRIC PHENOMENA

Why do these phenomena occur? What is the essence of these phenomena? We have to find out this in today's and coming lessons.

In notebooks, write down the date, class work, lesson topic.

Electrical phenomena

Each of you, by the end of the lesson, should learn to explain what an electric charge and electrification are, how charged bodies interact with each other, and how the simplest device is an electroscope.

Let's first consider the origin of the term "electricity"

The history of the development of electricity begins with Thales of Miletus. At first, the property of attracting small objects was attributed only to amber (petrified resin of coniferous trees). From the name of which the word electricity comes from, because the Greek. elektron-amber. (writing on the board)

3 student: Only at the end of the 16th century and the beginning of the 17th century did they remember this discovery. The English physician and naturalist Ulyam Gilbert (1544-1603) found out that friction can electrify many substances. He was one of the first scientists to validate experience, experiment, as the basis of research.

The scientific study of electrical phenomena began in the book of Hilbert, who also owns the term "electricity". Hilbert painstakingly examined many different bodies and built for this purpose a special electric pointer, which he describes as follows: "Make yourself an arrow of any metal three or four inches long, movable enough on your needle, like a magnetic pointer." With the help of this pointer, the prototype of modern electroscopes, Hilbert established that many bodies, "not only created by nature, but also artificially prepared, have the ability to attract." He showed that during friction, not only amber is electrified, but also many other substances: diamond, sapphire, sealing wax, and that they attract not only straws, but also metals, wood, leaves, pebbles, lumps of earth, and even water and oil. However, he found that many bodies "are not attracted or excited by any rubbing." These include a number of precious stones and metals: “silver, gold, copper, iron, also any magnet”. Bodies exhibiting the ability to attract, Hilbert called electrical, bodies that do not have this ability - non-electrical.

Teacher: If a piece of amber is rubbed against wool or a glass stick - on paper or silk, then you can hear a slight crackle, sparks in the dark, and the stick itself acquires the ability to attract small objects to itself

A body that, after rubbing, attracts other bodies to itself, is said to be electrified or that it has been given an electric charge.

Experience 1. Let's electrify the comb on dry hair

By the attraction of bodies to each other, one can judge whether an electric charge is imparted to the bodies.There are devices with which one can judge the electrification of bodies - an electroscope (an electron - I observe)

An electroscope is a physical device used to detect an electrical charge on a body.

The electroscope has a cylindrical body into which a metal rod passes, isolated from the body by a plastic stopper. Is there a metal ball at one end of the rod, and at the other? two movable petals.

When a charged body touches the ball of the electroscope, its petals are deflected by a certain angle, depending on the magnitude of the charge, the greater the charge of the electroscope, the greater the repulsive force of the leaves. The electrometer is similarly arranged, in it a light arrow is repelled from the rod.

To discharge the electroscope, you can simply touch it with your hand. You can do this, for example, with an iron or copper wire, but the charges will not go into the ground along a glass or ebony stick.

Electrification can occur in several ways:

1. BY TOUCH

Newton was also engaged in electrical experiments, who observed the electrical dance of pieces of paper placed under glass placed on a metal ring. When rubbing the glass, the pieces of paper were attracted to it, then bounced off, again attracted, etc. These experiments were carried out by Newton as early as 1675.

2. BY IMPACT (the rubber hose will sharply hit a massive object and bring it to the electroscope)

3.FRICTION

Hilbert points out how electrification is produced by friction: “They are rubbed with bodies that do not spoil their surface and make them shine, for example, with hard silk, rough non-marking cloth and dry palms. They also rub amber on amber, on diamond, on glass and much more. This is how electrical bodies are processed. ”

Bodies rub against each other to increase their area of ​​contact.

Test 2. Place plastic wrap on the paper strip and press firmly on the strips with your hand. Spread the strips apart, and then bring them closer to each other.

Strips ______________________.

Conclusion: bodies can be electrified ___ friction ___________.

____ are always involved in electrification. two _______ bodies.

electrified after separation _____ both _____ bodies.

We made a very important conclusion:

• One of the types of electrification is the friction of bodies.
• In this case, always two (or more) bodies are involved.
• Both bodies become electrified.

As you noticed, two bodies are always involved in electrification: amber with fur; glass with silk, etc. In this case, both bodies are electrified.

Student 4: Electrification is also observed when liquids rub against metals during flow, as well as splashing on impact. For the first time, electrification of a liquid during crushing was noticed near waterfalls in Switzerland in 1786. Since 1913, the phenomenon has been called the balloelectric effect.

The conqueror of Chomolungma N. Tenzing in 1953, in the region of the southern saddle of this mountain peak at an altitude of 7.9 km above sea level at 30 ° C and dry winds up to 25 m / s, observed strong electrification of icy tarpaulin tents, inserted one into the other. The space between the tents was filled with numerous electric sparks. The movement of avalanches in the mountains on moonless nights is sometimes accompanied by a greenish-yellow glow, due to which the avalanches become visible.

All electrified bodies attract other bodies to themselves, such as pieces of paper. By attraction, one cannot distinguish the electric charge of a glass rod, rubbed against silk, from the charge received from an ebony stick, rubbed against fur. After all, both electrified sticks attract pieces of paper to themselves.

5 student: Charles Dufet (1698-1739) established two kinds of electrical interactions: attraction and repulsion. First, he established that “electrified bodies attract non-electrified ones and immediately repulse them as soon as they become electrified due to proximity or contact with electrified bodies”. Later he discovered "another principle, more general and more remarkable than the previous ones." “This principle,” continues Dufay, “is that there are two kinds of electricity, which are highly different from each other: I call one kind“ glass ”electricity, the other“ resinous ”... with him and attract the opposite. So, for example, a body electrified with glass electricity repels all bodies with glass electricity, and, conversely, it attracts bodies with resin electricity. Likewise, resin repels resin and attracts glass. ”

Teacher: So, electric charge? it is a measure of the properties of charged bodies to interact with each other.

What types of interactions do you know? (attraction and repulsion)

Conventionally, the charges were called positive (rubbed against silk on glass) and negative (on amber, ebonite, sulfur, rubber rubbed against wool).

A positive charge in physics is denoted + q or q

Negative charge - -q

6 student: The concept of positive and negative charges, was introduced in 1747 by Franklin. The ebony stick from electrification on wool and fur is charged negatively, because V. Franklin called the charge formed on the rubber stick negative. And ebonite is a rubber with a large admixture of sulfur. The charge, which forms on a glass rod, rubbed against silk, Franklin called positive. But in Franklin's time there was only natural silk and natural fur. Today it is sometimes difficult to distinguish natural silk and faux fur. Even different grades of paper electrify ebonite in different ways. Ebonite acquires a negative charge from contact with wool (fur) and nylon, but positive from contact with polyethylene.

Teacher: Let's see how charged bodies interact

Video demonstration.

So, bodies with electric charges of the same sign are mutually repelled, and bodies with charges of the opposite sign are mutually attracted. (see supporting synopsis)

According to the ability to conduct electrical charges, all bodies are divided into conductors and non-conductors (dielectrics).

Open the tutorial on pages 62-63, find the definition of conductors and dielectrics.

Conductors: metals, soil, aqueous solutions or electrolyte melts.

Dielectrics: Plastics, air, gases, glass, rubber, silk, porcelain, kerosene, nylon, etc.

What bodies are called insulators

Bodies made of dielectrics are called insulators.

Primary control: Now we will carry out a small test task, which you will check with each other and give your grades right away. You are given five minutes to complete.

Option 1

1. The glass is charged when rubbed against silk:

• positively
• negatively.

2. If an electrified body is repelled by an ebony stick, rubbed against the fur, then it is charged:

• positively;
• negatively.

3. Three pairs of light balls are suspended on threads. Which pair of balls is not charged?

4. Which pair of balls (see the same figure) has the same charges?

5. Which pair of balls (see the same figure) has opposite charges?

Option 2.

1. When rubbing against the fur, the rubber is electrified:

• positively;
• negatively.

2. If a charged body is attracted to a glass rod rubbed on silk, then it is charged:

• positively;
• negatively.

3. Three pairs of light balls are suspended on threads. Which pair of balls has the same charges?

4. Which pair of balls has opposite charges (see the same figure)?

5. Which pair of balls is not charged (see the same figure)?

Answers:

Option 1 ABAVB

Option 2 BBAVB

Anchoring: Listen to the proverb and answer the questions:

• What physical phenomenon (concept, law) is it talking about?
• What is the physical meaning of the proverb? Is it correct from the point of view of physics?
• What is the everyday meaning of this proverb?

Proverbs

Like straw and amber (Persian)

That a silk ribbon clings to the wall (Russian)

QUALITATIVE OBJECTIVES

1. What precautions must be taken so that when gasoline is poured from one tank to another, it does not ignite? (During transportation and when pouring, gasoline is electrified, a spark may occur, and the gasoline will ignite. To prevent this from happening, both tanks and the pipeline connecting them are grounded).
2. To ground the tank of the fuel tanker, a steel chain is attached to it, the lower end of which touches the ground with several links. Why is there no such chain on the railroad tank car? (Because the rail tank car is grounded through the rail wheels)
3. Can one and the same body, for example, an ebonite stick, become electrified under friction, sometimes negatively, sometimes positively? (Maybe depending on what it is rubbed with)
4. If you take out one nylon stocking from the other and hold each in your hand in the air, then they expand. Why? (Under friction, the stockings are electrified. Charges of the same name are repelled. Therefore, the surface of the stocking swells.)

Electric charges do so many useful things that it is impossible to list them all.

For example, smoking is the soaking of a product with wood smoke. Smoke particles not only give the food a special taste, but also protect it from deterioration. During electric smoking, particles of smoke smoke are charged positively, and, for example, fish carcasses are connected to negative electrodes. Charged smoke particles settle on the surface of the carcass and are partially absorbed. The whole process of electric smoking takes several minutes.

Lesson summary. Grading

Why wear a gold ring
On a finger when two get engaged? -
A curious maiden asked me.
Without becoming confused by the question,
I replied to my dear interlocutor:
Love has electric power,
And gold is a guide!