How many types of electric charges exist in nature? I

Similar to the concept gravitational mass body in Newtonian mechanics, the concept of charge in electrodynamics is the primary, basic concept.

Electric charge - This physical quantity, characterizing the property of particles or bodies to enter into electromagnetic force interactions.

Electric charge is usually represented by the letters q or Q.

The totality of all known experimental facts allows us to draw the following conclusions:

There are two types of electric charges, conventionally called positive and negative.

Charges can be transferred (for example, by direct contact) from one body to another. Unlike body mass, electric charge is not an integral characteristic of a given body. The same body different conditions may have a different charge.

Like charges repel, unlike charges attract. This also reveals a fundamental difference electromagnetic forces from gravitational ones. Gravitational forces are always forces of attraction.

One of the fundamental laws of nature is the experimentally established conservation law electric charge .

In an isolated system algebraic sum the charges of all bodies remain constant:

q 1 + q 2 + q 3 + ... +qn= const.

The law of conservation of electric charge states that in a closed system of bodies processes of creation or disappearance of charges of only one sign cannot be observed.

WITH modern point From our point of view, charge carriers are elementary particles. All ordinary bodies consist of atoms, which include positively charged protons, negatively charged electrons and neutral particles - neutrons. Protons and neutrons are part of atomic nuclei, electrons form electron shell atoms. The electric charges of a proton and an electron are exactly the same in magnitude and equal to the elementary charge e.

In a neutral atom, the number of protons in the nucleus is equal to the number of electrons in the shell. This number is called atomic number . Atom of this substance may lose one or more electrons or gain an extra electron. In these cases, the neutral atom turns into a positively or negatively charged ion.

Charge can be transferred from one body to another only in portions containing an integer number of elementary charges. Thus, the electric charge of a body is a discrete quantity:

Physical quantities that can only take discrete series values ​​are called quantized . Elementary charge e is a quantum ( the smallest portion) electric charge. It should be noted that in modern physics elementary particles the existence of so-called quarks is assumed - particles with a fractional charge and However, quarks have not yet been observed in a free state.

In ordinary laboratory experiments used to detect and measure electrical charges electrometer ( or electroscope) - a device consisting of a metal rod and a pointer that can rotate around a horizontal axis (Fig. 1.1.1). The arrow rod is isolated from the metal body. When a charged body comes into contact with the electrometer rod, electric charges of the same sign are distributed over the rod and the pointer. Electrical repulsion forces cause the needle to rotate through a certain angle, by which one can judge the charge transferred to the electrometer rod.

The electrometer is a rather crude instrument; it does not allow one to study the forces of interaction between charges. The law of interaction of stationary charges was first discovered by the French physicist Charles Coulomb in 1785. In his experiments, Coulomb measured the forces of attraction and repulsion of charged balls using a device he designed - a torsion balance (Fig. 1.1.2), which was extremely different high sensitivity. For example, the balance beam was rotated 1° under the influence of a force of the order of 10 -9 N.

The idea of ​​​​the measurements was based on Coulomb's brilliant guess that if a charged ball is brought into contact with exactly the same uncharged one, then the charge of the first will be divided equally between them. Thus, a way was indicated to change the charge of the ball by two, three, etc. times. In Coulomb's experiments, the interaction between balls whose dimensions were much smaller than the distance between them was measured. Such charged bodies are usually called point charges.

Point charge called a charged body, the dimensions of which can be neglected in the conditions of this problem.

Based on numerous experiments, Coulomb established the following law:

The interaction forces between stationary charges are directly proportional to the product of the charge moduli and inversely proportional to the square of the distance between them:

Interaction forces obey Newton's third law:

They are repulsive forces when identical signs charges and attractive forces at different signs(Fig. 1.1.3). The interaction of stationary electric charges is called electrostatic or Coulomb interaction. The branch of electrodynamics that studies the Coulomb interaction is called electrostatics .

Coulomb's law is valid for point charged bodies. In practice, Coulomb's law is well satisfied if the sizes of charged bodies are much smaller than the distance between them.

Proportionality factor k in Coulomb's law depends on the choice of system of units. IN International system SI unit of charge is taken pendant(Cl).

Pendant is the charge passing through the cross section conductor at a current of 1 A. The unit of current (Ampere) in SI is, along with units of length, time and mass basic unit of measurement.

Coefficient k in the SI system it is usually written as:

Where - electrical constant .

In the SI system elementary charge e equal to:

Experience shows that the Coulomb interaction forces obey the superposition principle:

If a charged body interacts simultaneously with several charged bodies, then the resulting force acting on this body is equal to vector sum forces acting on this body from all other charged bodies.

Rice. 1.1.4 explains the principle of superposition using the example of the electrostatic interaction of three charged bodies.

The principle of superposition is a fundamental law of nature. However, its use requires some caution when we're talking about about the interaction of charged bodies of finite sizes (for example, two conducting charged balls 1 and 2). If a third charged ball is brought to a system of two charged balls, then the interaction between 1 and 2 will change due to charge redistribution.

The principle of superposition states that when given (fixed) charge distribution on all bodies, the forces of electrostatic interaction between any two bodies do not depend on the presence of other charged bodies.

By hanging light balls of foil on two threads and touching each of them with a glass rod rubbed on silk, you can see that the balls will repel each other. If you then touch one ball with a glass rod rubbed on silk, and the other with an ebonite rod rubbed on fur, the balls will attract each other. This means that glass and ebonite rods, when rubbed, acquire charges of different signs , i.e. exist in nature two types of electric charges having opposite signs: positive and negative. We agreed to assume that a glass rod rubbed on silk acquires positive charge , and an ebonite stick, rubbed on fur, acquires negative charge .

From the described experiment it also follows that charged bodies interact with each other. This interaction of charges is called electrical. Wherein charges of the same name, those. charges of the same sign , repel each other, and unlike charges attract each other.

The device is based on the phenomenon of repulsion of similarly charged bodies electroscope- a device that allows you to determine whether a given body is charged, and electrometer, a device that allows you to estimate the value of electric charge.

If you touch the rod of an electroscope with a charged body, the leaves of the electroscope will disperse, since they will acquire a charge of the same sign. The same thing will happen to the needle of an electrometer if you touch its rod with a charged body. In this case, the greater the charge, the greater the angle the arrow will deviate from the rod.

From simple experiments it follows that the force of interaction between charged bodies can be greater or less depending on the amount of charge acquired. Thus, we can say that the electric charge, on the one hand, characterizes the body’s ability to interact electrically, and on the other hand, is a quantity that determines the intensity of this interaction.

The charge is indicated by the letter q , taken as a unit of charge pendant: [q ] = 1 Cl.

If you touch one electrometer with a charged rod, and then connect this electrometer with a metal rod to another electrometer, then the charge on the first electrometer will be divided between the two electrometers. You can then connect the electrometer to several more electrometers, and the charge will be divided between them. Thus, the electric charge has property of divisibility . The charge divisibility limit, i.e. the smallest charge existing in nature is the charge electron. The electron charge is negative and equal to 1.6*10 -19 Cl. Any other charge is a multiple of the electron charge.

1 .Two types of electric charges and their properties. The smallest indivisible electrical charge. Law of conservation of electric charges. Coulomb's law. Unit of charge. Electrostatic field. Field detection method. Tension as a characteristic electrostatic field. Tension vector, its direction. Tension electric field point charge. Tension units. The principle of superposition of fields.

Electric charge - the quantity is invariant, i.e. does not depend on the reference frame, and therefore does not depend on whether the charge is moving or at rest.

two kinds (types) of electric charges : positive charges and negative charges.

It has been experimentally established that like charges repel, and unlike charges attract.

An electrically neutral body must have an equal number of positive and negative charges, but their distribution throughout the volume of the body must be uniform.

Law of conservation of el. charge : algebraic sum of elec. charges of any closed system (a system that does not exchange charges with external heat) remains unchanged, no matter what processes occur within this system.

Elek. charges are not spontaneously created and do not arise, they can only be separated and transferred from one body to another.

Exists the smallest charge, it was called the elementary charge - this is the charge that an electron has and the charge on the body is a multiple of this elementary charge: e=1.6*10 -19 Cl. A negative elementary charge is associated with an electron, and a positive one is associated with a positron, whose charge and mass quantitatively coincide with the charge and mass of the electron. However, due to the fact that the positron lifetime is short, they are absent on bodies and therefore the positive or negative charge of bodies is explained by either a lack or excess of electrons on the bodies.

Coulomb's Law: the forces of interaction between two point charges located in a homogeneous and isotropic medium are directly proportional to the product of these charges and inversely proportional to the square of the distance between them, are equal to each other and are directed in a straight line passing through these charges. g is the distance between charges q 1 and q 2, k is the proportionality coefficient, depending on the choice of the system of physical units.

m/F, a =8.85*10 -12 F/m - dielectric constant

Under point charge we should understand charges concentrated on bodies whose linear dimensions are small compared to the distances between them.

In this case, charge is measured in coulombs - the amount of electricity flowing through the cross-section of a conductor in one second at a current of 1 ampere.

The force F is directed along the straight line connecting the charges, i.e. is the central force and corresponding to attraction (F<0) в случае разноименных зарядов и отталкиванию (F>0) in the case of charges of the same name. This force is called Coulomb force.

Faraday's later research showed that electrical interaction between charged bodies depend on the properties of the medium in which these interactions occur.

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

Gray's published experiments aroused the interest of the French physicist Charles Francois Dufay (1698–1739) and prompted him to begin experiments in the field of studying 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 pushes away from the wax stick, as if avoiding it. If you now bring a glass tube rubbed against 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 unelectrified ones, and as soon as the latter are electrified by touch, they begin to repel each other. He establishes the existence of two opposite types 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 are electrified either like glass rubbed on skin or like resin rubbed on fur. Consequently, there are two types of electric charges, and similar charges repel each other, and dissimilar charges attract. Electric interaction forces

charges that manifest themselves in attraction or repulsion are called electric. That is electrical forces are created by electric charges and act on charged bodies or particles.

An excess of charges of any one type in this body called the magnitude of its charge, or, otherwise, the amount of electricity (q).

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

A very successful designation of the two types of electricity, which has survived to this day, was given by the outstanding American physicist Benjamin Franklin.

"Resin" electricity was called negative by Franklin, and "glass" electricity was called positive. He chose these names because “resin” and “glass” electricity, like positive and negative quantities, cancel each other out.

The phenomena of electrification are explained by the structural features of atoms and molecules various substances. After all, all bodies are built from atoms. Each atom consists of a positively charged atomic nucleus and negatively charged particles moving around it - electrons. Atomic nuclei various chemical elements are not the same, but differ in charge and mass. The 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 of 1 coulomb, let's calculate the force of interaction between two charges of one coulomb each, placed in a vacuum at a distance of 1 m from each other. Using the formula of Coulomb's law, we find 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 an attractive or repulsive interaction force F on each other in the direction of the line of their connection, depending on whether they are similarly or differently electrified. equal to the product their point electric charges (q 1 and q 2, respectively) divided by the square of the distance r between them. That is

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

At in good condition of an atom, the positive charge of its nucleus is equal to the total negative charge of the electrons of that atom, so that any atom in the normal state is electrically neutral. But under the influence external influences atoms can lose some of their electrons, while the charge of their nuclei remains unchanged. In this case, the atoms become positively charged and are called positive ions. Atoms can also gain additional electrons 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 he called a torsion balance (Fig. 5.3).

F = (q 1 q 2 )/4 π ε a r 2 ,

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

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

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.

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Lesson objectives:

Educational

• introduce students to new physical phenomenon electrification of bodies and its features;
• prove the existence of two types of charges and explain their interaction;
• reveal the importance of electrification for human life.

Developmental

• continue to develop the skills to put forward a hypothesis and test (or refute) it experimentally;
• develop the ability to analyze, draw conclusions, generalize;
• improve the skill of self-educational activities.

Educational

• develop communication skills, ability to work in a group;
• personal qualities students: organization, attention, accuracy.

Health-saving

• creating a comfortable psychological climate at the lesson;
• atmosphere of cooperation: student-teacher, teacher-student, student-student.

Lesson type: lessons of learning new material.

Form of organization educational activities students: collective, group work, individual work at a desk and at the blackboard.

Equipment: computer, screen, equipment for physical experiment, didactic materials.

Lesson plan:

1. Organizational stage.
2. Updating knowledge, deducing the topic and purpose of the lesson through searching for an answer to problematic issue and analysis of slide materials.
3. Studying new material using frontal and demonstration experiments; through putting forward a hypothesis and its experimental proof, working with additional (historical) material and a student’s presentation on the topic: “The harm and benefits of electrification.”
4. Physical exercise.
5. Fixing the material. Frontal experiment. Work in groups. Research activities. Executing the test.
6. Lesson summary. Homework. Reflection.

During the classes

I. Organizational stage.

(Self-assessment of readiness for the lesson.)

II. Updating knowledge, deducing the purpose of the lesson.

Guys, we have finished studying the large chapter “Thermal Phenomena”.

Today we begin to study a new big chapter.

Well, guess what we will talk about in this chapter?

It brings us light and warmth
Computer, video includes
Comfortable with him, but without him
Conveniences disappear instantly.

Answer: electricity.

The words "electricity" and " electricity“are now familiar to every person. And the topic we are about to study is very important. Why do you think? (Electric current is used in our homes, in transport, in factories, in agriculture etc. And in nature there is electricity: lightning, auroras, electric fish and many other phenomena).

Slides 1-4.

To understand what electric current, electricity, is, you must first become familiar with a large range of phenomena called electric. Chapter III is called “Electrical Phenomena”.

Today in class we will study two questions from this chapter: “Electrification of bodies. Two types of charges."

Write the topic of the lesson in your notebook.

Let's determine the purpose of our lesson, what questions will we consider in the lesson? (What is electrification? What properties does it have? What charges exist in nature? Does the phenomenon of electrification bring benefit or harm?)

Slide 5.

III. Learning new material.

Our lesson takes place on the eve of the New Year. And in New Year many miracles happen.

Today in the lesson I also have an assistant for performing miracles - it’s an ordinary wand made of ebonite (I draw the children’s attention to the note on the board: ebonite is rubber with an admixture of sulfur). I will try to create a miracle with her help. I'll try to get something out of this beautiful box.

Does not work. What to do? (say a spell)

I'll try. Kribli-Krabli-Booms! It doesn't work again...

Do you remember what Aladdin did when he took the genie out of the lamp? (rubbed the lamp)

I’ll try to rub my stick on a woolen rag.

Happened. And the wand, it turns out, is magic. After rubbing, it began to attract small pieces of paper, hair, fluff, and even a thin stream of water.

a) Frontal experiment. You guys have a plastic ruler and a piece of paper on your desks. Check, maybe the ruler is also magic? (rub the ruler on a sheet of paper)

Yes, light objects stick to the ruler after rubbing.

So what interesting property bodies we saw in the experiments carried out?

(the body after rubbing attracts other bodies)

This “miracle” that we observed has a name – “electrification”.

And about a body that, after rubbing, attracts other bodies to itself, physicists say that it is electrified or that an electric charge is imparted to it.

These properties of bodies were noticed in ancient times, in the 6th century BC. e.

Let's listen to the legend. Slide 6

The daughter of the Greek philosopher Thales of Miletus spun wool with an amber spindle. Once, having dropped the spindle into the water, the girl began to wipe it with the edge of her woolen chiton and noticed that several hairs had stuck to the spindle. Thinking that they were stuck to the spindle because it was still wet, she began to wipe it even harder. And what? The more the spindle was rubbed, the more fur stuck to it. The girl turned to her father for an explanation of this phenomenon. Thales realized that the reason was in the substance from which the spindle was made, he bought various amber products and became convinced that all of them, when rubbed with woolen matter, attract light objects, just as a magnet attracts iron.

“Amber” in Greek means electron, hence the words “electricity”, “ electrical phenomena“,” “electrification” (I draw the children’s attention to the note on the board: amber is the fossilized resin of coniferous trees that lived millions of years ago; I show beads made of amber).

Let's try to formulate what electrification is?

Electrification is the process of imparting an electrical charge to the body. Slide 7

How many bodies are involved in the process of electrification? (two bodies are involved in electrification)

I have another one in my hands Magic wand– glass. I bring it to the pieces of paper, but we don’t see anything. I rub it on the silk, again bring it to the pieces of paper, hairs, and we see that they are attracted to the stick. What can we say about the stick? (she is electrified or given an electric charge).

We can say about one of the bodies that it is electrified, can we also say about the other that it is electrified? A hypothesis is put forward. How to test a hypothesis? ( Demonstration experiment)

Conclusion: both bodies are electrified.

Write down all your findings in your notebook.

b) Two types of charges Slide 8.

In 1733, the French botanist and physicist Charles Duffet discovered two types of charges - charges resulting from the friction of two resinous substances (he called them “resinous electricity”) and charges resulting from the friction of glass and mica (“glass electricity”). And the American physicist and political figure Benjamin Franklin in 1778 replaced the term "glass electricity" with "positive" and "tar" with "negative". These terms have taken root in science.

A positive charge is indicated by a “+” sign. negative sign «-».

Slide 9.

Glass rubbed on silk is charged with a positive charge - “+”

Ebonite rubbed on wool is charged negative charge – «-»

We draw a diagram on the board and in notebooks:

We explore how bodies charged with different charges behave; identical charges.

Experiments with sultans.

1. Bodies with charges of the same kind repel each other.

2. Bodies with charges various kinds, are mutually attracted.

Write down your findings in your notebook.

IV. Fizminutka.

Let's move a little (form pairs).

You are positive charges. Draw their interaction.

Some of you have a positive charge, the other a negative charge. Draw their interaction.

You are negative charges. Draw their interaction. Slide 10.

Student presentation on the topic: “Electrification is useful and harmful” Appendix 1Slides 11-12.

V. Consolidation

a) Frontal experiment.

1. You have two strips of polyethylene and two strips of paper on your table. Place a strip of polyethylene on the strip of polyethylene. Stroke them with the back of your hand. Try to separate them, and then slowly bring them closer together. What are you observing? (repulsion) How were the strips charged?

Now place a strip of polyethylene on the strip of paper. Stroke them with the back of your hand. Try to separate them, and then slowly bring them closer together. What are you observing? (attraction). How did the strips charge?

b) Research work.

While doing the work, draw up a plan for conducting an experiment to determine the sign of the charge, tell each other the order of your actions.

1st group. Determine the sign of the charge obtained on a plastic ruler rubbed against a dry sheet of paper. Determine the necessary devices yourself.

2nd group. Having at your disposal a plastic comb, an ebonite stick, a plume, a cloth, determine the sign of the charge received on the comb when combing your hair.

3rd group. The butterfly suspended from a tripod on a silk thread is charged, but it is not known what the sign of its charge is. How, given a glass rod and a piece of silk, can you determine the sign of charge on a butterfly?

c) test(done on a double sheet, carbon paper is inserted between the sheets; the top sheet is handed in, the bottom one remains with the student for checking and self-assessment of the work performed)

1. How do a charged stick and a paper sleeve interact in the case of A and in case b?

1. What sign of charge does the left ball have in the case A and in case b?

1. Are the interactions of charged bodies depicted correctly?

1. The paper cartridges hanging nearby became electrified. After that, they were positioned as shown in the figure. Did the cartridges receive the same or different charges?

Slide 13

VI. Lesson summary. Homework. Reflection.

(we electrify smiley balloons and attach them to the wall above the board; children go to the board and put a plus under the chosen smiley.)

§25, 26. Learn the notes in the notebook.

Task to choose from:

1. Write down examples of electrification that you encounter at home.
2. Conduct an electrification experiment with objects available at home.
3. Swipe research work on the topic “Electrification of bodies” according to plan:
   1. Purpose of the study.
   2. Equipment.
   3. Progress of the study.
   4. Conclusions.

The results of the work can be presented in the form of a presentation, description or photographs, etc.

Internet resources:

1. shi51.ucoz.ru/index/elektrizaciya_tel_8/0-58
2. wiki.edc.samara.ru/index.php/