Electrons and charged particles. Electric charge. Electric charge and elementary particles. Law of conservation of charge Elementary particle without electric charge

Electric charge is a property of particles and physical bodies that characterizes their interaction with external and internal electromagnetic fields. Electrons are the simplest charged particles. As is known from elementary school physics, any physical body consists of molecules, and those, in turn, of atoms. Any atom consists of a positively charged nucleus and negatively charged electrons rotating around the nucleus in orbits, similar to the rotation of planets around the Sun.
Charged objects are attracted to other charged particles or objects. From the same school physics, we remember the simplest practical experiments with electric charges. For example, if you take a balloon and quickly rub it on a jumper, and then put the worn side against the wall, the balloon will stick to it. This happened because we charged the balloon, and an electrical force of attraction appeared between it and the wall. (Although the wall was initially uncharged, a charge was induced on it when approaching it balloon.)
Electrically charged bodies and particles come in two types: negative and positive. Like charges attract each other, and like charges repel. A good analogy for this is ordinary magnets, which are attracted to each other by opposite poles and repelled by like poles. As we have already said, electrons have a negative charge, and atomic nuclei have a positive charge (the nucleus contains positively charged protons, as well as neutrons that have no electrical charge). IN nuclear physics particles are also considered - positrons, which are similar in properties to electrons, but have positive charge. Although the positron is only a physical and mathematical abstraction, positrons have not been found in nature.
If we don't have positrons, then how can we charge an object positively? Suppose there is an object that has been negatively charged because there are 2000 free (that is, not associated with the nuclei of specific atoms) electrons on its surface.
Considering another similar object that has only 1000 free electrons on its surface, we can say that the first object is more negatively charged than the second. But we can also say that the second object is more positively charged than the first. It is simply a matter of what is mathematically accepted as the origin and from what point of view one looks at the charges.
To charge our balloon, we need to do some work and expend energy. You need to overcome the friction of the balloon on the woolen jumper. During friction, electrons move from one surface to another. Consequently, one object (the balloon) gained an excess of free electrons and became negatively charged, while the wool jumper lost the same number of free electrons and became positively charged.
Electricity. Electromotive force. Work of electric current

Therefore, the balloon should stick to the jumper. Or not? Of course, it will be attracted to the jumper, since these two bodies have electric charges of opposite signs. But what happens when they touch? The balloon will not stick! This happens because the positively charged fibers of the jumper will touch the negatively charged areas of the balloon, and free electrons from the surface of the balloon will be attracted by the jumper and return to it, thus neutralizing the charge.
When the ball came into contact with the jumper, a flow of free electrons appeared between them, which is always accompanied by electrical phenomena. From this point on, you can stop abstract conversations about balls and jumpers, and go directly to electrical engineering.
An electron is a very small particle (and whether it is a particle at all, or a bunch of energy - physicists have not yet come to a consensus on this matter) and has a small charge, so a more convenient unit of measurement of electric charge is needed than the number of free electrons on the surface of a charged body. Such a convenient unit of measurement of electric charge is the coulomb (C). Now we can say that if the difference in electric charges between two bodies is 1 coulomb, then approximately 6,180,000,000,000,000,000 electrons will be moved during their interaction. Of course, measuring in pendants is much more convenient!

Morgan Jones
Tube Amplifiers
Translation from English under the general scientific editorship of Ph.D. Assoc. Ivanyushkina R Yu.

With the words “electricity”, “electric charge”, “ electricity“You have met many times and managed to get used to them. But try to answer the question: “What is an electric charge?” - and you will see that it is not so simple. The fact is that the concept of charge is a basic, primary concept that cannot be reduced at the current level of development of our knowledge to any simpler, elementary concepts

Let us first try to find out what is meant by the statement: a given body or particle has an electric charge.

You know that all bodies are built from tiny particles, indivisible into simpler (as far as science now knows) particles, which are therefore called elementary. All elementary particles have mass and due to this they are attracted to each other according to the law universal gravity with a force that decreases relatively slowly as the distance between them increases, inversely proportional to the square of the distance. Most elementary particles, although not all, also have the ability to interact with each other with a force that also decreases in inverse proportion to the square of the distance, but this force is a huge number of times greater than the force of gravity. So. in the hydrogen atom, shown schematically in Figure 91, the electron is attracted to the nucleus (proton) with a force 101" times greater than the force of gravitational attraction.

If particles interact with each other with forces that slowly decrease with increasing distance and are many times greater than the forces of gravity, then these particles are said to have an electric charge. The particles themselves are called charged. There are particles without an electric charge, but there is no electric charge without a particle.

Interactions between charged particles are called electromagnetic. Electric charge - physical quantity, which determines the intensity electromagnetic interactions, just as mass determines the intensity of gravitational interactions.

The electric charge of an elementary particle is not a special “mechanism” in the particle that could be removed from it, decomposed into its component parts and reassembled. The presence of an electric charge on an electron and other particles only means the existence

certain force interactions between them. But we, in essence, do not know anything about charge if we do not know the laws of these interactions. Knowledge of the laws of interactions should be included in our ideas about charge. These laws are not simple; it is impossible to state them in a few words. This is why it is impossible to give a sufficiently satisfactory brief definition of what an electric charge is.

Two signs of electric charges. All bodies have mass and therefore attract each other. Charged bodies can both attract and repel each other. This most important fact, familiar to you from the VII class physics course, means that in nature there are particles with electric charges of opposite signs. If the charge signs are the same, the particles repel, and if they are of different signs, they are attracted.

The charge of elementary particles - protons, which are part of all atomic nuclei, is called positive, and the charge of electrons is called negative. There are no intrinsic differences between positive and negative charges. If the signs of the particle charges were reversed, then the nature of electromagnetic interactions would not change at all.

Elementary charge. In addition to electrons and protons, there are several other types of charged elementary particles. But only electrons and protons can exist in a free state indefinitely. The rest of the charged particles live less than a millionth of a second. They are born during collisions of fast elementary particles and, having existed for an insignificantly short time, decay, turning into other particles. You will become acquainted with these particles in class X.

Neutrons are particles that do not have an electrical charge. Its mass is only slightly greater than the mass of a proton. Neutrons, together with protons, are part of atomic nucleus.

If an elementary particle has a charge, then its value, as numerous experiments have shown, is strictly definite (one of such experiments - the experiment of Millikan and Ioffe - was described in a textbook for grade VII)

There is a minimum charge, called elementary, that all charged elementary particles possess. The charges of elementary particles differ only in signs. It is impossible to separate part of the charge, for example from an electron.

« Physics - 10th grade"

First, let's consider the simplest case, when electrically charged bodies are at rest.

The branch of electrodynamics devoted to the study of the equilibrium conditions of electrically charged bodies is called electrostatics.

What is an electric charge?
What charges are there?

With words electricity, electric charge, electric current you have met many times and managed to get used to them. But try to answer the question: “What is an electric charge?” The concept itself charge- this is a basic, primary concept that cannot be reduced at the current level of development of our knowledge to any simpler, elementary concepts.

Let us first try to find out what is meant by the statement: “ This body or the particle has an electrical charge.”

All bodies are built from the smallest particles, which are indivisible into simpler ones and are therefore called elementary.

Elementary particles have mass and due to this they are attracted to each other according to the law of universal gravitation. As the distance between particles increases, the gravitational force decreases in inverse proportion to the square of this distance. Most elementary particles, although not all, also have the ability to interact with each other with a force that also decreases in inverse proportion to the square of the distance, but this force is many times greater than the force of gravity.

So in the hydrogen atom, shown schematically in Figure 14.1, the electron is attracted to the nucleus (proton) with a force 10 39 times greater than the force of gravitational attraction.

If particles interact with each other with forces that decrease with increasing distance in the same way as the forces of universal gravity, but exceed the gravitational forces many times, then these particles are said to have an electric charge. The particles themselves are called charged.

There are particles without an electric charge, but there is no electric charge without a particle.

The interaction of charged particles is called electromagnetic.

Electric charge determines the intensity of electromagnetic interactions, just as mass determines the intensity of gravitational interactions.

The electric charge of an elementary particle is not a special mechanism in the particle that could be removed from it, decomposed into its component parts and reassembled. The presence of an electric charge on an electron and other particles only means the existence of certain force interactions between them.

We, in essence, know nothing about charge if we do not know the laws of these interactions. Knowledge of the laws of interactions should be included in our ideas about charge. These laws are not simple, and it is impossible to outline them in a few words. Therefore, it is impossible to give a sufficiently satisfactory short definition concept electric charge.

Two signs of electric charges.

All bodies have mass and therefore attract each other. Charged bodies can both attract and repel each other. This most important fact, familiar to you, means that in nature there are particles with electric charges of opposite signs; in the case of charges of the same sign, the particles repel, and in the case of different signs, they attract.

Charge of elementary particles - protons, which are part of all atomic nuclei, are called positive, and the charge electrons- negative. There are no internal differences between positive and negative charges. If the signs of the particle charges were reversed, then the nature of electromagnetic interactions would not change at all.

Elementary charge.

In addition to electrons and protons, there are several other types of charged elementary particles. But only electrons and protons can exist in a free state indefinitely. The rest of the charged particles live less than a millionth of a second. They are born during collisions of fast elementary particles and, having existed for an insignificantly short time, decay, turning into other particles. You will become familiar with these particles in 11th grade.

Particles that do not have an electrical charge include neutron. Its mass is only slightly greater than the mass of a proton. Neutrons, together with protons, are part of the atomic nucleus. If an elementary particle has a charge, then its value is strictly defined.

Charged bodies Electromagnetic forces in nature play a huge role due to the fact that all bodies contain electrically charged particles. The constituent parts of atoms - nuclei and electrons - have an electrical charge.

The direct action of electromagnetic forces between bodies is not detected, since the bodies in their normal state are electrically neutral.

An atom of any substance is neutral because the number of electrons in it is equal to the number of protons in the nucleus. Positively and negatively charged particles are bonded to each other electrical forces and form neutral systems.

A macroscopic body is electrically charged if it contains an excess amount of elementary particles with any one sign of charge. Thus, the negative charge of a body is due to the excess number of electrons compared to the number of protons, and the positive charge is due to the lack of electrons.

In order to obtain an electrically charged macroscopic body, that is, to electrify it, you need to separate part negative charge from the positive charge associated with it or transfer a negative charge to a neutral body.

This can be done using friction. If you run a comb through dry hair, then a small part of the most mobile charged particles - electrons - will move from the hair to the comb and charge it negatively, and the hair will charge positively.

Equality of charges during electrification

With the help of experiment, it can be proven that when electrified by friction, both bodies acquire charges that are opposite in sign, but identical in magnitude.

Let's take an electrometer, on the rod of which there is a metal sphere with a hole, and two plates on long handles: one made of hard rubber and the other made of plexiglass. When rubbing against each other, the plates become electrified.

Let's bring one of the plates inside the sphere without touching its walls. If the plate is positively charged, then some of the electrons from the needle and rod of the electrometer will be attracted to the plate and collected on the inner surface of the sphere. At the same time, the arrow will be charged positively and will be pushed away from the electrometer rod (Fig. 14.2, a).

If you bring another plate inside the sphere, having first removed the first one, then the electrons of the sphere and the rod will be repelled from the plate and will accumulate in excess on the arrow. This will cause the arrow to deviate from the rod, and at the same angle as in the first experiment.

Having lowered both plates inside the sphere, we will not detect any deviation of the arrow at all (Fig. 14.2, b). This proves that the charges of the plates are equal in magnitude and opposite in sign.

Electrification of bodies and its manifestations. Significant electrification occurs during friction of synthetic fabrics. When you take off a shirt made of synthetic material in dry air, you can hear a characteristic crackling sound. Small sparks jump between the charged areas of the rubbing surfaces.

In printing houses, paper is electrified during printing and the sheets stick together. To prevent this from happening, special devices are used to drain the charge. However, the electrification of bodies in close contact is sometimes used, for example, in various electrocopying installations, etc.

Law of conservation of electric charge.

Experience with the electrification of plates proves that during electrification by friction, a redistribution of existing charges occurs between bodies that were previously neutral. A small portion of electrons moves from one body to another. In this case, new particles do not appear, and pre-existing ones do not disappear.

When bodies are electrified, law of conservation of electric charge. This law is valid for a system into which charged particles do not enter from the outside and from which they do not leave, i.e. for isolated system.

In an isolated system, the algebraic sum of the charges of all bodies is conserved.

q 1 + q 2 + q 3 + ... + q n = const. (14.1)

where q 1, q 2, etc. are the charges of individual charged bodies.

The law of conservation of charge has a deep meaning. If the number of charged elementary particles does not change, then the fulfillment of the charge conservation law is obvious. But elementary particles can transform into each other, be born and disappear, giving life to new particles.

However, in all cases, charged particles are born only in pairs with charges of the same magnitude and opposite in sign; Charged particles also disappear only in pairs, turning into neutral ones. And in all these cases, the algebraic sum of the charges remains the same.

The validity of the law of conservation of charge is confirmed by observations of a huge number of transformations of elementary particles. This law expresses one of the most fundamental properties electric charge. The reason for the charge conservation is still unknown.