Electric charges, their interaction.
DC electric circuit, its basic laws.
Electronic theory of the structure of matter.
All substances in nature are made up of molecules, molecules of atoms.
Molecule is the smallest particle that has the chemical properties of a given substance.
Atom is the smallest particle that has the chemical and physical properties of a given element.
It consists of:
a positively charged nucleus
negative electrons rotating in allowed orbits.
The nucleus consists of positive protons and neutral neutrons.
The charge of an electron is equal to the charge of a proton, but the signs are opposite. These elementary particles are not equal in size and mass, the proton is larger than the electron.
An atom is an electrically neutral particle (not charged), that is, as many protons are in the nucleus, so many electrons revolve around the nucleus, since one proton can hold one electron.
Thus, the diversity of the world around us is formed from various combinations of only three particles: a neutron, a proton and an electron, which in turn also have an internal structure.
Valence electrons are the electrons that are in the extreme orbit. They determine the chemical properties of a substance and its electrical conductivity.
Electrical conductivity is the ability of a substance to conduct an electric current.
Electric charges, their interaction.
Even in ancient times, it was known that amber, worn on wool, acquires the ability to attract light objects. Later it was found that many other substances have a similar property. Bodies capable, like amber, after rubbing attract light objects, are called electrified. On bodies in this state there are electric charges, and the bodies themselves are called charged.
In nature, there are only two types of charges - positive and negative. Charges of the same sign (like charges) repel, charges of opposite signs (opposite charges) attract.
Elementary particles have the smallest (elementary) charge. For example, a proton and a positron are positively charged, while an electron and an antiproton are negatively charged.
The elementary negative charge is equal in magnitude to the elementary positive charge. In the SI system, charge is measured in pendants(CL). The value of the elementary charge e \u003d 1.6-10-19 C. In nature, nowhere and never does an electric charge of the same sign arise and disappear. The appearance of a positive electric charge + q is always accompanied by the appearance of an equal negative electric charge - q. Neither positive nor negative charges can disappear separately from one another, they can only mutually neutralize each other if they are equal.
To get a charge from a neutral atom, you need to act with some kind of force and tear off electrons, or attach foreign electrons to a neutral atom. As a result, upon separation (for example, during friction), a positively charged atom is obtained, which is called positive ion, and when attached - negative ion.
Ionization is the process of formation of charges from a neutral atom.
8.1. Two types of electric charges
If some particles (or bodies) have the ability to take part in electrical interactions, then it makes sense to attribute to them some characteristic that will indicate this property of them. This characteristic is called electric charge. Bodies that take part in electrical interactions are called charged. Thus, the term "electrically charged" is synonymous with the expression "participates in electrical interactions." Why some elementary particles have an electric charge, while others do not - no one knows!
Further reasoning, based on experimental data, is intended to concretize this characteristic, if possible, to make it quantitative.
The history of the study of electrical phenomena is long and full of drama, ...
Next, we describe a series of simple experiments that can be carried out at home "in the kitchen" or in the school laboratory. When explaining them, we will use the knowledge that has been obtained by many scientists over several hundred years, as a result of numerous and varied experiments.
Now, we will reproduce in a very simplified form some stages of experimental research, the conclusions from which served as the basis for the modern theory of electrical interactions.
To conduct experiments, first of all, one should learn how to obtain charged bodies. The simplest way to achieve this goal is electrification by friction. For example, glass is well electrified (that is, acquires an electric charge) if it is rubbed with silk. The appearance of an electric charge is manifested in the fact that such a stick begins to attract pieces of paper, hairs, dust particles, etc.
It can also be established that many other substances are also electrified by friction. Knowing the result in advance, as the second "source" of electricity, we choose an ebonite stick worn with wool. Let's call the electric charge that appears on the glass - "glass", and the charge on ebonite "resin".
Next, we need a "device" that could respond to the presence of an electric charge. To do this, we hang a light cup twisted from a piece of foil on a thread. It is easy to check that this cup is not charged - so that we do not bring a pencil, hand, physics textbook, etc. to it, no effect on the cup appears.
Let's bring a charged glass electric stick to an uncharged glass (Fig. 141). The glass is attracted to it, like other small bodies. From the angle of deviation of the thread (with a known mass of the cup and the length of the thread), one can even calculate the force of attraction. If the glass does not come into contact with a charged stick, it remains uncharged, which can be easily verified experimentally. If the glass touches the charged stick, then it will sharply push away from it. If we now remove the wand, the cup will be charged, which can be verified by bringing another uncharged body close to it. For example, it will be attracted to the raised hand.
Similar results are obtained if we replace a glass rod rubbed on silk with an ebonite rod rubbed on wool.
Thus, in these experiments, the difference between "glass" and "resin" electricity does not appear.
We will not yet discuss why an uncharged cup is attracted to a charged stick, and a charged cup is attracted to an uncharged hand. The only conclusion that we can draw from the experiment is that as a result of contact, the glass acquired an electric charge. Therefore, the electric charge can be transmitted from one body to another.
Take two identical foil cups, hang them side by side on threads of the same length. If the cups are charged in the same way (either with the help of a glass or with the help of an ebonite rod), then the cups are repelled (Fig. 142). If the cups are charged with different charges, then they attract.
Thus, we prove that there is at least two types of electric charges.
For further experiments, we will replace the "measuring cups" with a more advanced device called an electrometer (Fig. 143). The device consists of a metal rod and a light metal pointer that can rotate around a horizontal axis. This device is placed in a metal case, closed with glass covers. The deflection angle of the pointer can be measured using a scale. The arrow rod is fixed in the body with a plexiglass sleeve. The rod with the arrow plays the same role as the foil cups in the previous experiments - when a charged body touches the rod, the charge will flow to the rod and to the arrow, which will lead to its deflection. Moreover, the direction of deflection of the arrow does not depend on the type of reported charge.
For further experiments, we will use two identical electroscopes. Let's charge one of them using, for example, a glass rod. Next, we will begin to connect the rods of electrometers using various materials. When connecting the rods with wooden, uncharged glass, ebonite, plastic sticks; textile threads, no changes occur - one electrometer remains charged, the second uncharged. If you connect the rods with a metal wire, then both electrometers are charged. Moreover, the deviation of the arrow of the initially charged electrometer will decrease (Fig. 144).
Two important conclusions can be drawn from the results of this experiment: firstly, some materials (metals) can transmit an electric charge, others (glass, plastic, wood) cannot; secondly, the charge can change, be more or less. The same experiments can be repeated using the second type (“resin”) electricity. The results will be the same - materials that conduct "glass" electricity conduct "resin" electricity. If the "glass" charge is redistributed between the electrometers, then the "resin" charge also behaves.
So, we can divide materials into two groups - those that transmit an electric charge (these materials are called conductors), and those that do not transmit an electric charge (they were called insulators). By the way, the rod of the electrometer is separated from the body with the help of an insulator sleeve so that the electric charge does not “spread” over the body, but remains on the rod and the arrow.
Various deviations of the electrometer needle clearly indicate that the force of interaction between charged bodies can be different, therefore, the magnitude of the charges can be different. Therefore, the charge can be characterized by some numerical value (and not, as we said earlier - “is, or is not”).
Another interesting result - if you touch the rod of a charged electrometer with your hand, then the electrometer is discharged - the charge disappears. Even on the basis of these qualitative observations, it is possible to explain where the charge disappears when the hand is touched. The human body is a conductor, so the charge can flow into the human body.
To confirm this idea about the quantitative nature of the charge, the following experiment can be carried out. We charge one electrometer - we note the angle of deviation of the arrow. We connect it to the second electrometer - the angle of deviation of the arrow will noticeably decrease. We remove the contact between the devices and the hand, discharge the second electrometer, after which we connect the electrometers again - the deviation of the arrow will decrease again. Thus, the electric charge can be divided into parts. You can also conduct the reverse experiment - gradually adding charge to the electrometer.
"Mix" now, the two available types of electricity. To do this, we charge one electrometer with “glass” electricity, and the second with “resin”, trying to ensure that the initial deviations of the arrows of both electrometers are approximately the same. After that, we connect the rods of the electrometers with a metal wire (on an insulating handle so that the charges do not run away). The result of this experiment may be surprising - both electroscopes were discharged, or "glass" and "resin" electricity neutralized, compensated each other (Fig. 145). Consequently, it turns out to be possible to assign different algebraic signs to different types of charge - to call one charge positive, the second negative. It is reasonable to assume that the force of interaction depends on the total charge. If initially the electrometers were charged with different types of electricity, but to a different extent (the deviations of the arrows are different), and then they are connected, then only partial compensation of charges will occur - the arrows will be deflected, but to a much lesser extent.
Historically, the "glass" charge was called positive, and the "resin" charge became negative.
The device described by us, the electrometer, allows only a qualitative assessment of the magnitude of the charges; it is impossible to carry out quantitative measurements with it. Try, for example, to bring your hand to a charged electrometer (without touching the rod) - the deviation of the arrow will increase! Bring a charged stick to an uncharged rod without touching the rod - the arrow will deviate, although the electrometer is not charged. We will return to the explanation of these facts later.
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, then the balls will be attracted to each other. This means that glass and ebonite rods acquire charges of different signs , i.e. exist in nature two kinds of electric charges having opposite signs: positive and negative. We agreed to consider that a glass rod, rubbed on silk, acquires positive charge , and an ebonite stick, rubbed against fur, acquires negative charge .
It also follows from the described experiment that charged bodies interact with each other. This interaction of charges is called electric. Wherein similar charges, those. charges of the same sign , repel each other, and opposite charges attract each other.
The device is based on the phenomenon of repulsion of like-charged bodies electroscope- an instrument to determine whether a given body is charged, and electrometer, a device that allows you to estimate the value of an electric charge.
If a charged body touches the rod of an electroscope, then the leaves of the electroscope will disperse, since they will acquire a charge of the same sign. The same will happen with the needle of the electrometer if the charged body touches its rod. 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 magnitude of the acquired charge. Thus, we can say that the electric charge, on the one hand, characterizes the ability of the body to electrical interaction, and on the other hand, is a quantity that determines the intensity of this interaction.
The charge is denoted by the letter q , taken as a unit of charge pendant: [q ] = 1 cl.
If you touch one electrometer with a charged stick, 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 shared between them. Thus, the electric charge has divisibility property . The limit of charge divisibility, i.e. the smallest charge that exists in nature is the charge electron. The charge of an electron is negative and equal to 1.6 * 10 -19 C. Any other charge is a multiple of the electron charge.
§ 1 Two types of electric charges. Interaction of electric charges
The structure of the universe is formed by gravitational attraction, but only this force would lead to unlimited compression. In order for the dimensions of bodies to remain stable, a repulsive force is needed. These forces include the forces of electromagnetic interaction. They cause attraction and repulsion of particles. Electrodynamics is a branch of physics that studies the electromagnetic interaction of charged particles. Electrostatics is a section of electrodynamics that studies the interaction of motionless (static) electric charges.
What is an electric charge? To create a representation, initial information, knowledge, experiences, experiments and hypotheses are necessary.
Electrical interaction (as opposed to gravitational) is not only mutual attraction, but also repulsion.
Let's conduct an experiment: we bring an ebonite stick, electrified by friction, first to one "sultan", then to the second. We will see that the leaves will repel when we bring the "sultans" to each other (Fig. 1).
We electrify the second "sultan" with a stick made of glass, worn on silk. Let's bring it to the first "sultan", and we will see the attraction of their leaves (Fig. 2, 3).
Electric charges existing in nature (positive and negative) can be confirmed by these experiments.
Bodies with an electric charge interact with each other as follows:
attract if they have charges of the opposite sign (Fig. 4);
repel if they have charges of the same sign (Fig. 5).
In the process of electrization of different bodies, the force of interaction between the bodies will be greater (if the body has a large charge) or less (if the body has a small charge). Thus, charge is a physical quantity, and 1 pendant (1C) is considered to be the unit of charge.
Electric charge is a physical measure that characterizes the properties of charged bodies to interact with each other.
The smallest portion of the charge is the elementary charge, it is equal to 1.6 10-19 C. The charge of any body cannot be less than this value.
If you electrify an ebonite stick with a woolen mitten, and a glass stick with a silk scarf, then hanging the sticks on threads, you can see that:
Ebonite and wool attract each other;
Glass and silk attract each other;
Glass and wool repel each other;
Ebonite and silk repel each other.
We electrify two bodies by friction, while they are charged with equal in magnitude and opposite in sign charges. Due to the contact, the first body loses electrons, the other acquires them. This can explain why on one body there will be an excess of electrons (negative charge), and on the other - a deficiency (positive charge).
Conclusion: if the body is negatively charged, then it has an excess of electrons, but if it
positively charged, it lacks electrons.
Two electrified bodies attract or repel, it depends on how they are electrified. Bodies that are electrified by friction always only attract.
In conductors, some electrons can move from one atom to another, this process occurs due to the fact that the electrons are weakly bound to the atomic nucleus. They are called free. It is these atoms that provide charge transfer (conductivity).
There is practically no conductivity in dielectrics, because they have almost no free electrons and "no one" to carry the charge.
According to electrical properties, all substances can be divided into two types:
1. Dielectrics - substances that do not have free charges and do not allow the charge of one body to "flow" to other bodies.
2. Conductors are bodies and substances in which there are free charged particles; they can move, while transferring the charge to other parts of the body or to other bodies.
According to the ability to conduct charges, substances can be divided into conductors: metals, soil, solutions of salts and acids, etc., and non-conductors (dielectrics): porcelain, ebonite, glass, gases, plastics, etc. Semiconductors include a number of substances, the conductivity of which depends on external conditions (temperature, illumination, the presence of impurities).
An electrometer is a device for detecting electric charges and determining their approximate value (Fig. 6).
To determine whether the body is charged or not, you can use an electrometer. To do this, you need to bring the body to the ball A, if the body is charged, then the arrow B will deviate. Why is she declining? Suppose the body had a negative charge, i.e. there was an excess of electrons on the body. When in contact with the ball, some of the electrons will move to the electrometer. The ball will become negatively charged. The ball is connected to the rod, and the rod is connected to the arrow, and they are all conductors, the electrons will move to the rod, and then to the arrow. A plastic stopper will help in isolating the ball, rod, arrow system. Consequently, the rod and the arrow will receive the same negative charge and will repel, thereby the arrow will deviate. Moreover, the greater the charge, the greater the angle of deflection of the arrow. The electrometer only allows you to estimate the magnitude of the charge, i.e. say that one body has more charge than the other. Using an electrometer, it is impossible to determine the presence of a small charge, because. with a small charge, the repulsive force of like charges will not be enough to deflect the arrow, i.e. using an electrometer it is impossible to determine the presence of a small charge. Why does the arrow return to its original position in the absence of a charge? The arrow will tend to assume a vertical position, since the point of suspension of the arrow is above the center of gravity.
Topics of the USE codifier: electrization of bodies, interaction of charges, two types of charge, law of conservation of electric charge.
Electromagnetic interactions are among the most fundamental interactions in nature. Forces of elasticity and friction, gas pressure and much more can be reduced to electromagnetic forces between particles of matter. The electromagnetic interactions themselves are no longer reduced to other, deeper types of interactions.
An equally fundamental type of interaction is gravity - the gravitational attraction of any two bodies. However, there are several important differences between electromagnetic and gravitational interactions.
1. Not everyone can participate in electromagnetic interactions, but only charged bodies (having electric charge).
2. Gravitational interaction is always the attraction of one body to another. Electromagnetic interactions can be both attraction and repulsion.
3. The electromagnetic interaction is much more intense than the gravitational one. For example, the electric repulsion force of two electrons is several times greater than the force of their gravitational attraction to each other.
Every charged body has some amount of electric charge. Electric charge is a physical quantity that determines the strength of the electromagnetic interaction between objects of nature. The unit of charge is pendant(CL).
Two types of charge
Since the gravitational interaction is always an attraction, the masses of all bodies are non-negative. But this is not the case for charges. Two types of electromagnetic interaction - attraction and repulsion - are conveniently described by introducing two types of electric charges: positive and negative.
Charges of different signs attract each other, and charges of different signs repel each other. This is illustrated in fig. one ; balls suspended on threads are given charges of one sign or another.
Rice. 1. Interaction of two types of charges
The ubiquitous manifestation of electromagnetic forces is explained by the fact that charged particles are present in the atoms of any substance: positively charged protons are part of the atomic nucleus, and negatively charged electrons move in orbits around the nucleus.
The charges of a proton and an electron are equal in absolute value, and the number of protons in the nucleus is equal to the number of electrons in orbits, and therefore it turns out that the atom as a whole is electrically neutral. That is why, under normal conditions, we do not notice the electromagnetic effect from the surrounding bodies: the total charge of each of them is zero, and the charged particles are evenly distributed throughout the volume of the body. But if electrical neutrality is violated (for example, as a result of electrification) the body immediately begins to act on the surrounding charged particles.
Why there are exactly two types of electric charges, and not some other number of them, is not currently known. We can only assert that the acceptance of this fact as primary gives an adequate description of electromagnetic interactions.
The charge of a proton is Cl. The charge of an electron is opposite to it in sign and is equal to C. Value
called elementary charge. This is the minimum possible charge: free particles with a smaller charge were not found in the experiments. Physics cannot yet explain why nature has the smallest charge and why its magnitude is precisely that.
The charge of any body is always the sum of the whole number of elementary charges:
If , then the body has an excess number of electrons (compared to the number of protons). If, on the contrary, the body lacks electrons: there are more protons.
Electrification of bodies
In order for a macroscopic body to exert an electrical influence on other bodies, it must be electrified. Electrification- this is a violation of the electrical neutrality of the body or its parts. As a result of electrification, the body becomes capable of electromagnetic interactions.
One of the ways to electrify a body is to impart an electric charge to it, that is, to achieve an excess of charges of the same sign in a given body. This is easy to do with friction.
So, when rubbing a glass rod with silk, part of its negative charges goes to the silk. As a result, the stick is charged positively, and the silk is negatively charged. But when rubbing an ebonite stick with wool, part of the negative charges transfers from the wool to the stick: the stick is charged negatively, and the wool is positively charged.
This method of electrification of bodies is called electrification by friction. You encounter electrification by friction every time you take off a sweater over your head ;-)
Another type of electrification is called electrostatic induction, or electrification through influence. In this case, the total charge of the body remains equal to zero, but is redistributed so that positive charges accumulate in some parts of the body, and negative charges in others.
Rice. 2. Electrostatic induction
Let's look at fig. 2. At some distance from the metal body there is a positive charge. It attracts the negative charges of the metal (free electrons), which accumulate on the areas of the body surface closest to the charge. Uncompensated positive charges remain in the far regions.
Despite the fact that the total charge of the metallic body remained equal to zero, a spatial separation of charges occurred in the body. If we now divide the body along the dotted line, then the right half will be negatively charged, and the left half positively.
You can observe the electrification of the body using an electroscope. A simple electroscope is shown in Fig. 3 (image from en.wikipedia.org).
Rice. 3. Electroscope
What happens in this case? A positively charged rod (for example, previously rubbed) is brought to the electroscope disk and collects a negative charge on it. Below, on the moving leaves of the electroscope, uncompensated positive charges remain; pushing away from each other, the leaves diverge in different directions. If you remove the wand, then the charges will return to their place and the leaves will fall back.
The phenomenon of electrostatic induction on a grandiose scale is observed during a thunderstorm. On fig. 4 we see a thundercloud going over the earth.
Rice. 4. Electrification of the earth by a thundercloud
Inside the cloud there are ice floes of different sizes, which are mixed by ascending air currents, collide with each other and become electrified. In this case, it turns out that a negative charge accumulates in the lower part of the cloud, and a positive charge accumulates in the upper part.
The negatively charged lower part of the cloud induces positive charges on the surface of the earth. A giant capacitor appears with a colossal voltage between the cloud and the ground. If this voltage is sufficient to break through the air gap, then a discharge will occur - lightning, well known to you.
Law of conservation of charge
Let's return to the example of electrification by friction - rubbing the stick with a cloth. In this case, the stick and the piece of cloth acquire charges equal in magnitude and opposite in sign. Their total charge, as it was equal to zero before the interaction, remains equal to zero after the interaction.
We see here law of conservation of charge which reads: in a closed system of bodies, the algebraic sum of charges remains unchanged for any processes that occur with these bodies:
Closedness of a system of bodies means that these bodies can exchange charges only among themselves, but not with any other objects external to the given system.
When the stick is electrified, there is nothing surprising in the conservation of charge: how many charged particles left the stick - the same amount came to a piece of cloth (or vice versa). Surprisingly, in more complex processes, accompanied by mutual transformations elementary particles and number change charged particles in the system, the total charge is still conserved!
For example, in fig. 5 shows the process in which a portion of electromagnetic radiation (the so-called photon) turns into two charged particles - an electron and a positron. Such a process is possible under certain conditions - for example, in the electric field of the atomic nucleus.
Rice. 5. Creation of an electron–positron pair
The charge of the positron is equal in absolute value to the charge of the electron and is opposite to it in sign. The law of conservation of charge is fulfilled! Indeed, at the beginning of the process we had a photon whose charge is zero, and at the end we got two particles with zero total charge.
The law of conservation of charge (along with the existence of the smallest elementary charge) is today the primary scientific fact. Physicists have not yet succeeded in explaining why nature behaves in this way and not otherwise. We can only state that these facts are confirmed by numerous physical experiments.
