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. 1 ; 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.
« Physics - Grade 10 "
Let us first consider the simplest case, when electrically charged bodies are at rest.
The section of electrodynamics devoted to the study of the equilibrium conditions for electrically charged bodies is called electrostatics.
What is an electric charge?
What are the charges?
With words electricity, electric charge, electric current you 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 the main, primary concept, which at the present level of development of our knowledge cannot be reduced 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."
All bodies are built from the smallest particles, which are indivisible into simpler ones and therefore are 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 inversely with 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 gravitation, but exceed the forces of gravity many times over, then these particles are said to have an electric charge. The particles themselves are called charged.
There are particles without 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 a particle that could be removed from it, decomposed into its component parts and reassembled. The presence of an electric charge in an electron and other particles means only the existence of certain force interactions between them.
We, in essence, know nothing about the charge, if we do not know the laws of these interactions. Knowledge of the laws of interactions should be included in our understanding of the charge. These laws are not simple, and it is impossible to state them in a few words. Therefore, it is impossible to give a sufficiently satisfactory concise definition of the 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, is 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.
elemental charge.
In addition to electrons and protons, there are several more types of charged elementary particles. But only electrons and protons can exist indefinitely in a free state. The rest of the charged particles live less than millionths of a second. They are born during collisions of fast elementary particles and, having existed for a negligible time, decay, turning into other particles. You will get acquainted with these particles in the 11th grade.
Particles that do not have an electrical charge include neutron. Its mass only slightly exceeds the mass of a proton. Neutrons, along 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 the composition of all bodies includes electrically charged particles. The constituent parts of atoms - nuclei and electrons - have an electric charge.
The direct action of electromagnetic forces between bodies is not detected, since the bodies in the normal state are electrically neutral.
An atom of any substance is neutral, since the number of electrons in it is equal to the number of protons in the nucleus. Positively and negatively charged particles are connected to each other by electrical forces and form neutral systems.
A macroscopic body is electrically charged if it contains an excess number of elementary particles with any one charge sign. So, the negative charge of the body is due to an excess of the number of electrons in comparison with the number of protons, and the positive charge is due to the lack of electrons.
In order to obtain an electrically charged macroscopic body, i.e., to electrify it, it is necessary to separate part of the negative charge from the positive charge associated with it, or to transfer a negative charge to a neutral body.
This can be done with friction. If you run a comb over dry hair, then a small part of the most mobile charged particles - electrons will pass from the hair to the comb and charge it negatively, and the hair will be charged positively.
Equality of charges during electrification
With the help of experience, it can be proved 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 a metal sphere with a hole is fixed, and two plates on long handles: one of ebonite, and the other 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 the electrometer rod will be attracted to the plate and collect on the inner surface of the sphere. In this case, the arrow will be positively charged and repelled from the electrometer rod (Fig. 14.2, a).
If another plate is introduced inside the sphere, having previously removed the first one, then the electrons of the sphere and the rod will be repelled from the plate and accumulate in excess on the arrow. This will cause the arrow to deviate from the rod, moreover, by the same angle as in the first experiment.
Having lowered both plates inside the sphere, we will not find any deflection 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 taking off a shirt made of synthetic material in dry air, you can hear a characteristic crackle. Small sparks jump between charged areas of rubbing surfaces.
In printing houses, the paper becomes 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 machines, etc.
The law of conservation of electric charge.
Experience with the electrification of plates proves that when electrified by friction, the existing charges are redistributed between bodies that were previously neutral. A small part of the electrons passes from one body to another. In this case, new particles do not appear, and the previously existing ones do not disappear.
When electrifying bodies, law of conservation of electric charge. This law is valid for a system that does not enter from the outside and from which charged particles do not exit, 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 law of charge conservation 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 produced only in pairs with charges of the same modulus 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 of electric charge. The reason for the conservation of charge is still unknown.
The laws of electrolysis discovered by Faraday testify in favor of the existence of the smallest, indivisible quantities of electricity. During electrolysis, one mole of any - valence element transfers a charge 
coulombs ( - Faraday's constant). One atom (more precisely, an ion) thus has a charge
A monovalent ion has a charge 
, for divalent - charge, for trivalent - charge, etc.
This pattern is easy to understand if we accept that the charge 
is the smallest portion of the charge, the elementary charge.
But the laws of electrolysis can also be understood in the sense that is the average portion of the charge carried by a monovalent ion; the property of a valence ion to carry a charge many times greater would then have to be explained not by the atomic structure of electricity, but only by the properties of the ion. Therefore, to clarify the question of the existence of an elementary charge, direct experiments are needed to measure the smallest amounts of electricity. Such experiments were carried out by the American physicist Robert Milliken (1868-1953) in 1909.
The Millikan installation is shown schematically in Fig. 348. Its main part is a flat capacitor 2.3, on the plates of which, with the help of switch 4, a potential difference of one sign or another can be applied.
Rice. 348. Scheme of experience in measuring the elementary electric charge. X-ray tube 7 serves to change the charge of the drops; its radiation creates ions in the volume between plates 2 and 3, which, sticking to the drop, change its charge
The smallest drops of oil or other liquid are sprayed into vessel 1 using a spray bottle. Some of these drops through a hole in the top plate fall into the space between the condenser plates, illuminated by lamp 6. The drops are observed through a microscope through window 5; they look like bright stars on a dark background.
When there is no electric field between the plates of a capacitor, the drops fall down at a constant speed. When the field is turned on, uncharged drops continue to fall at a constant speed. But many droplets acquire a charge when sprayed (electrification by friction). Such charged drops are affected, in addition to the force of gravity, also by the force of the electric field. Depending on the sign of the charge, you can choose the direction of the field so that the electric force is directed towards the force of gravity. In this case, the charged drop after the field is turned on will fall at a lower speed than in the absence of the field. You can choose the value of the field strength so that the electric force will exceed the force of gravity and the drop will move up.
In the Millikan installation, one can observe the same drop for several hours; To do this, it suffices to turn off (or decrease) the field as soon as the drop begins to approach the upper plate of the capacitor, and turn it on (or increase) again when it descends to the bottom plate.
The uniformity of the drop movement indicates that the force acting on it is balanced by the air resistance, which is proportional to the drop velocity. Therefore, for such a drop, we can write the equality
where is the force of gravity acting on a drop with mass , is the velocity of the drop, is the force of air resistance (friction force), is a coefficient depending on the viscosity of the air and the size of the drop.
Having measured the diameter of the drop with a microscope, therefore, knowing its mass, and further determining the speed of free uniform fall , we can find from (196.1) the value of the coefficient , which remains unchanged for a given drop. The condition of uniform motion for a drop with a charge rising with a velocity in an electric field has the form
(196.2)
From (196.2) we get
Thus, having made measurements with the same drop in the absence of a field and in its presence, we will find the charge of the drop . We can change this charge. For this purpose, X-ray tube 7 (Fig. 348) is used, with which you can ionize the air in the condenser. The resulting ions will be captured by the droplet, and its charge will change, becoming equal to . In this case, the rate of uniform motion of the drop will change and it will become equal to , so that
This minimum charge is equal, as we see, to the elementary charge that appears in the process of electrolysis. It is important to note that the initial charge of the drop is "friction electricity", while changes in this charge occurred due to the capture by the drop of gas ions formed by X-rays. Thus, the charge formed during friction, the charges of gas ions and electrolyte ions are composed of identical elementary charges. Data from other experiments allow us to generalize this conclusion: all positive and negative charges occurring in nature consist of an integer number of elementary charges. 
.
In particular, the charge of an electron is equal in absolute value to one elementary charge.
Shock wave sensitivity
Shock wave action is created by a shock wave. The shock wave that enters the charge creates a zone of compressed matter in which decomposition reactions and energy release take place. If the rate of energy release is greater than the rate of its removal, then the shock wave front is accelerated, fed and propagated. If the velocity of the release energy is low, then the shock wave has time to move forward and die out.
The time of shock-wave action is short. If the duration of the initial pulse is less than the critical value (~0.11 μs) and the minimum velocity of the initiating shock wave is less than some critical value, then a failure occurs.
A complex shock-wave effect is usually created with the help of the explosion of other explosives. From a practical point of view, the sensitivity of explosives to this pulse is important in the creation of reliable means of initiation (CA) and in blasting for reliable transfer of a detonation pulse from one explosive charge to another.
Minimum initiating charge such an amount of explosives that is capable of causing a complete detonation of the explosives.
The minimum charge of the IVV depends not only on the sensitivity of the IVV to the detonation pulse, but also on the properties of the IVV. Therefore, in order to ensure the failure-free operation of the CA of the combined equipment, it is necessary to determine the minimum charge of a specific TCS included in the CA design, in relation to a specific CA. The test conditions are as close as possible to reality, i.e. equip subversive CD No. 8
(1 g BVV and some amount of IVV (<0,1 г).
Either a igniter cord or an electric igniter is inserted into the CD. The finished CD is mounted on a standard lead plate and undermined. If the diameter of the plate penetration is equal to or greater than the diameter of the sleeve, then the detonation of the BVV is complete. By changing the sample size of the IVV, the minimum charge is found. The minimum charge of the IVV depends on the density of the IVV. The higher the density, the greater the minimum charge. The presence of solid refractory impurities in the charge of BVV reduces the minimum charge, while fusible and soft impurities increase it.
The influence of the charge density of the explosives and impurities is associated with the mechanism of excitation of the explosion. Low density and refractory impurities contribute to the implementation of the focal mechanism of excitation of the explosion, which requires less energy.
A change in the mass of the BVV has practically no effect on the minimum charge of the VVV. A change in the diameter of the sleeve leads to a change in the thickness of the IVV layer. Therefore, the minimum charge is usually determined in the sleeve No. 8 or characterized by the ratio of the mass to the cross-sectional area of the charge.
We list the properties of charges
2. Electric charge has discrete nature
elementary charge
Electricity. Conditions for the existence of electric current. Current strength and current density
An electric current is a directed movement of charged particles. It was agreed to consider the direction of motion of positively charged particles as the direction of the electric current. For the continued existence of an electric current in a closed circuit, the following conditions must be met:
The presence of free charged particles (current carriers);
The presence of an electric field, the forces of which, acting on charged particles, make them move in an orderly manner;
The presence of a current source, inside which external forces move free charges against electrostatic (Coulomb) forces.
The quantitative characteristics of the electric current are the current strength I and the current density j.
The current strength is a scalar physical quantity equal to the ratio of the charge Δq passing through the cross section of the conductor over a certain period of time Δt to this interval:
The SI unit of current is the ampere (A).
If the strength of the current and its direction do not change with time, then the current is called constant.
The current density j is a vector physical quantity, the modulus of which is equal to the ratio of the current strength I in the conductor to the cross-sectional area S of the conductor:
The SI unit for current density is the ampere per square meter (A/m2).
Refraction of light in lenses
A lens is a transparent body bounded by two curvilinear or curvilinear and flat surfaces.
In most cases, lenses are used, the surfaces of which have a spherical shape. A lens is said to be thin if its thickness d is small compared to the radii of curvature of its surfaces R1 and R2. Otherwise, the lens is called thick. The main optical axis of a lens is called a straight line passing through the centers of curvature of its surfaces. We can assume that in a thin lens the points of intersection of the main optical axis with both surfaces of the lens merge into one point O, called the optical center of the lens. A thin lens has one main plane common to both surfaces of the lens and passing through the optical center of the lens perpendicular to its main optical axis. All straight lines passing through the optical center of the lens and not coinciding with its main optical axis are called secondary optical axes of the lens. Rays traveling along the optical axes of the lens (main and secondary) do not experience refraction.
Thin lens formula:
where n21 \u003d n2 / n1, n2 and n1 are the absolute refractive indices for the lens material and the environment, R1 and R2 are the radii of curvature of the front and rear (relative to the object) surfaces of the lens, a1 and a2 are the distances to the object and its image, counted from the optical the center of the lens along its main optical axis.
The value is called the focal length of the lens. Points lying on the main optical axis of the lens on both sides of the optical center at equal distances equal to f are called the main foci of the line. The planes passing through the main foci F1 and F2 of the lens perpendicular to its main optical axis are called the focal planes of the lens. The intersection points of the secondary optical axes with the focal planes of the lens are called secondary foci of the lens.
A lens is called converging (positive) if its focal length f>0. A lens is called diverging (negative) if its focal length f<0.
For n2 >n1 converging lenses are biconvex, plano-convex and concave-convex (positive meniscus lenses), thinning from the center to the edges; diffusing are biconcave, plano-concave and convex-concave lenses (negative menisci), thickening from the center to the edges. For p2
Planck's hypothesis. Photon and its properties. Wave-particle duality
Planck's hypothesis - a hypothesis put forward on December 14, 1900 by Max Planck and consisting in the fact that during thermal radiation, energy is emitted and absorbed not continuously, but in separate quanta (portions). Each such portion-quantum has an energy proportional to the frequency ν of the radiation:
where h or is the coefficient of proportionality, later called Planck's constant. Based on this hypothesis, he proposed a theoretical derivation of the relationship between the temperature of a body and the radiation emitted by this body - Planck's formula.
Planck's hypothesis was later confirmed experimentally.
The advancement of this hypothesis is considered the moment of the birth of quantum mechanics.
A photon is a material, electrically neutral particle, a quantum of an electromagnetic field (a carrier of electromagnetic interaction).
Basic properties of a photon
1. Is a particle of the electromagnetic field.
2. Moves at the speed of light.
3. Exists only in motion.
4. It is impossible to stop a photon: it either moves at a speed equal to the speed of light, or does not exist; therefore, the rest mass of a photon is zero.
Photon energy:
According to the theory of relativity, the energy can always be calculated as ,
Hence - the mass of the photon.
photon momentum. The photon momentum is directed along the light beam.
Wave-particle duality
The end of the 19th century: the photoelectric effect and the Compton effect confirmed Newton's theory, and the phenomena of diffraction and light interference confirmed Huygens' theory.
Thus, many physicists at the beginning of the 20th century. concluded that light has two properties:
1. When propagating, it exhibits wave properties.
2. When interacting with a substance, it exhibits corpuscular properties. Its properties are not limited to either waves or particles.
The more v, the more pronounced are the quantum properties of light and the less are the wave properties.
So, any radiation has both wave and quantum properties. Therefore, how a photon manifests itself - as a wave or as a particle - depends on the nature of the study carried out on it.
Rutherford's experiments. Planetary model of the atom
For an experimental study of the distribution of positive charge, and hence the mass inside the atom, Rutherford proposed in 1906 to apply the probing of the atom with the help of α-particles. Their mass is about 8000 times the mass of the electron, and the positive charge is equal in modulus to twice the charge of the electron. The speed of α-particles is very high: it is 1/15 of the speed of light. With these particles, Rutherford bombarded the atoms of heavy elements. Electrons, due to their small mass, cannot noticeably change the trajectory of the α-particle and are not able to noticeably change its speed. Scattering (changing the direction of motion) of α-particles can only be caused by the positively charged part of the atom. Thus, from the scattering of α-particles, one can determine the nature of the distribution of positive charge and mass inside the atom. A radioactive preparation, such as radium, was placed inside lead cylinder 1, along which a narrow channel was drilled. A beam of α-particles from the channel fell on thin foil 2 made of the material under study (gold, copper, etc.). After scattering, the α-particles hit a semitransparent screen 3 coated with zinc sulfide. The collision of each particle with the screen was accompanied by a flash of light (scintillation), which could be observed in a microscope 4. The entire apparatus was placed in a vessel from which the air was evacuated.
When distributed throughout the atom, a positive charge cannot create a sufficiently intense electric field capable of throwing the a-particle back. The maximum repulsive force is determined by Coulomb's law:
where qα is the charge of the α-particle; q is the positive charge of the atom; r is its radius; k - coefficient of proportionality. The electric field strength of a uniformly charged ball is maximum on the surface of the ball and decreases to zero as it approaches the center. Therefore, the smaller the radius r, the greater the force that repels the α-particles. This theory seems absolutely indispensable for explaining experiments on the scattering of a-particles. But on the basis of this model it is impossible to explain the existence of the atom, its stability. After all, the movement of electrons in orbits occurs with acceleration, and quite considerable. According to Maxwell's laws of electrodynamics, an accelerated charge must radiate electromagnetic waves with a frequency equal to the frequency of its circulation around the nucleus. Radiation is accompanied by a loss of energy. Losing energy, the electrons should approach the core, just as a satellite approaches the Earth when braking in the upper atmosphere. As rigorous calculations based on Newton's mechanics and Maxwell's electrodynamics show, an electron must fall on a nucleus in a negligible time. The atom must cease to exist.
In reality, nothing like this happens. It follows from this that the laws of classical physics are inapplicable to atomic-scale phenomena. Rutherford created a planetary model of the atom: electrons revolve around the nucleus, just as the planets revolve around the sun. This model is simple, justified experimentally, but does not allow explaining the stability of the atom.
Quantity of heat
The amount of heat is a measure of the change in internal energy that the body receives (or gives away) in the process of heat transfer.
Thus, both work and the amount of heat characterize the change in energy, but are not identical to energy. They do not characterize the state of the system itself, but determine the process of energy transfer from one form to another (from one body to another) when the state changes and essentially depend on the nature of the process.
The main difference between work and the amount of heat is that work characterizes the process of changing the internal energy of the system, accompanied by the transformation of energy from one type to another (from mechanical to internal). The amount of heat characterizes the process of transfer of internal energy from one body to another (from more heated to less heated), not accompanied by energy transformations.
Experience shows that the amount of heat required to heat a body of mass m from temperature T1 to temperature T2 is calculated by the formula where c is the specific heat of the substance;
The SI unit of specific heat is the joule per kilogram-Kelvin (J/(kg K)).
The specific heat capacity c is numerically equal to the amount of heat that must be imparted to a body of mass 1 kg in order to heat it by 1 K.
The heat capacity of the body CT is numerically equal to the amount of heat required to change the body temperature by 1 K:
The SI unit of heat capacity of a body is the joule per Kelvin (J/K).
To change a liquid into a vapor at a constant temperature, the amount of heat required is
where L is the specific heat of vaporization. When steam condenses, the same amount of heat is released.
In order to melt a crystalline body of mass m at the melting point, it is necessary to inform the body of the amount of heat 
where λ is the specific heat of fusion. During the crystallization of a body, the same amount of heat is released.
The amount of heat that is released during the complete combustion of fuel of mass m,
where q is the specific heat of combustion.
The SI unit of specific heats of vaporization, melting, and combustion is joule per kilogram (J/kg).
Electric charge and its properties. discreteness. elementary electric charge. The law of conservation of electric charge.
Electric charge is a physical quantity that characterizes the electromagnetic interaction. The body is negatively charged if there is an excess of electrons on it, positively - a deficit.
We list the properties of charges
1. There are two kinds of charges; negative and positive. Opposite charges attract, like charges repel. The carrier of the elementary, i.e. The smallest, negative charge is an electron, whose charge is qe = -1.6 * 10-19 C, and the mass is me = 9.1 * 10-31 kg. The carrier of the elementary positive charge is the proton qр=+1.6*10-19C, mass mр=1.67*10-27kg.
2. Electric charge has discrete nature. This means that the charge of any body is a multiple of the electron charge q=Nqe, where N is an integer. However, as a rule, we do not notice the discreteness of the charge, since the elementary charge is very small.
3. In an isolated system, i.e. in a system whose bodies do not exchange charges with bodies external to it, the algebraic sum of charges is conserved (the charge conservation law).
4. Email charge can always be transferred from one body to another.
5. The unit of charge in SI is the pendant (C). By definition, 1 pendant is equal to the charge flowing through the cross section of the conductor in 1 s at a current of 1 A.
6. The law of conservation of electric charge.
Inside a closed system, for any interactions, the algebraic sum of electric charges remains constant:
An isolated (or closed) system we will call a system of bodies into which no electric charges are introduced from the outside and are not removed from it.
Nowhere and never in nature does an electric charge of the same sign arise and disappear. The appearance of a positive electric charge is always accompanied by the appearance of a negative charge equal in absolute value. Neither a positive nor a negative charge can disappear separately, they can only mutually neutralize each other if they are equal in absolute value.
So elementary particles are able to transform into each other. But always at the birth of charged particles, the appearance of a pair of particles with charges of the opposite sign is observed. The simultaneous birth of several such pairs can also be observed. Charged particles disappear, turning into neutral ones, also only in pairs. All these facts leave no doubt about the strict implementation of the law of conservation of electric charge.
elementary charge- the minimum charge that cannot be divided.
