Coulomb's law states that. Coulomb's law. point charge
It is known that every charged body has electric field. It can also be argued that if there is an electric field, then there is a charged body to which this field belongs. So, if there are two charged bodies with electric charges nearby, then we can say that each of them is in the electric field of a neighboring body. And in this case, the force will act on the first body
F 1 =q 1E 2 ,
where q 1 is the charge of the first body; E 2- field strength of the second body. On the second body, respectively, the force will act
F 2 =q2E 1 ,
where q2 is the charge of the first body; E 1- field strength of the second body.
An electrically charged body interacts with the electric field of another charged body.
If these bodies are small (point-like), then
E 1 =k . q 1 / r 2 ,
E 2 =k .q 2 /r2,
The forces acting on each of the interacting charged bodies can be calculated knowing only their charges and the distance between them.
Substitute the values of tension and get
F 1 \u003d k. q 1 q 2 / r 2 and F 2 \u003d k. q 2 q 1 / r 2 .
The value of each force is expressed only through the value of the charges of each body and the distance between them. Thus, it is possible to determine the forces acting on each body using only knowledge of the electric charges of bodies and the distance between them. On this basis, one of the fundamental laws of electrodynamics can be formulated - Coulomb's law.
Coulomb's law . The force acting on a fixed point body with an electric charge in the field of another fixed point body with an electric charge is proportional to the product of the values of their charges and inversely proportional to the square of the distance between them.
AT general view the meaning of the force that in question in the wording Coulomb's law, can be written like this:
F=k. q 1 q 2 / r 2 ,
In the formula for calculating the interaction force, the values \u200b\u200bof the charges of both bodies are written. Therefore, we can conclude that both forces are equal in modulus. However, in direction they are opposite. If the charges of the bodies are of the same name, the bodies repel each other (Fig. 4.48). If the charges of the bodies are different, then the bodies are attracted (Fig. 4.49). Finally, you can write:
F̅ 1 = -F̅ 2 .
The recorded equality confirms the validity of Newton's III law of dynamics for electrical interactions. Therefore, in one of the common formulations Coulomb's law says that
the force of interaction between two charged point bodies is proportional to the product of the values of their charges and inversely proportional to the square of the distance between them.
If the charged bodies are in a dielectric, then the interaction force will depend on the permittivity of this dielectric
F=k .q 1q 2 /ε r2.
For the convenience of calculations based on the Coulomb law, the value of the coefficient k written differently:
k = 1 / 4πε 0 .
Value ε 0 called electric constant. Its value is calculated according to the definition:
nine . 10 9 N.m 2 / C 2 \u003d 1 / 4π ε 0 ,
ε 0 = (1 / 4π) . nine . 10 9 N.m 2 / C 2 \u003d 8.85. 10 -12 C 2 /N.m 2 . material from the site
In this way, Coulomb's law in general case can be expressed by the formula
F= (1 / 4π ε 0 ) . q 1 q 2 / ε r 2 .
Coulomb's law is one of the fundamental laws of nature. All electrodynamics is based on it, and not a single case has been noted when the Coulomb's law. There is only one restriction that concerns the action Coulomb's law on various distances. It is believed that Coulomb's law operates at distances greater than 10 -16 m and less than a few kilometers.
When solving problems, it is necessary to take into account that Coulomb's law concerns the interaction forces of point motionless charged bodies. This reduces all problems to problems about the interaction of motionless charged bodies, in which two positions of statics are used:
- the resultant of all forces acting on the body is zero;
- the sum of the moments of forces is equal to zero.
In the vast majority of tasks for the application Coulomb's law it is enough to take into account only the first position.
On this page, material on the topics:
Write down the formula for Coulomb's law
Coulomb's law abstract
Report on physics on the topic Coulomb's law
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Coulomb's law is a law describing the forces of interaction between point electric charges.
It was discovered by Charles Coulomb in 1785. a large number of experiments with metal balls, Charles Coulomb gave the following formulation of the law:
The module of the interaction force of two point charges in a vacuum is directly proportional to the product of the modules of these charges and inversely proportional to the square of the distance between them
Otherwise: Two point charges in vacuum act on each other with forces that are proportional to the product of the modules of these charges, inversely proportional to the square of the distance between them and directed along the straight line connecting these charges. These forces are called electrostatic (Coulomb).
It is important to note that in order for the law to be true, it is necessary:
- point charges - that is, the distance between charged bodies is much greater than their size - however, it can be proved that the force of interaction of two volumetrically distributed charges with spherically symmetric non-intersecting spatial distributions is equal to the force of interaction of two equivalent point charges located at the centers of spherical symmetry;
- their immobility. Otherwise, additional effects come into force: the magnetic field of the moving charge and the corresponding additional Lorentz force acting on another moving charge;
- interaction in a vacuum.
However, with some adjustments, the law is also valid for interactions of charges in a medium and for moving charges.
In vector form, in the formulation of S. Coulomb, the law is written as follows:
where is the force with which charge 1 acts on charge 2; - the magnitude of the charges; - radius vector (vector directed from charge 1 to charge 2, and equal, in absolute value, to the distance between charges - ); - coefficient of proportionality. Thus, the law indicates that charges of the same name repel (and opposite charges attract).
Coefficient k
In the CGSE, the unit of charge is chosen in such a way that the coefficient k is equal to one.
AT international system units (SI) one of the basic units is the unit of force electric current ampere, and the unit of charge - the pendant - is a derivative of it. The ampere is defined in such a way that k= c2 10-7 H/m = 8.9875517873681764 109 N m2/C2 (or F−1 m). In SI coefficient k is written as:
where ≈ 8.854187817 10−12 F/m is the electrical constant.
In a homogeneous isotropic substance, the relative permittivity of the medium ε is added to the denominator of the formula.
Coulomb's law in quantum mechanics
AT quantum mechanics Coulomb's law is not formulated using the concept of force, as in classical mechanics, but with the help of the concept of the potential energy of the Coulomb interaction. In the case when the system considered in quantum mechanics contains electrically charged particles, the terms expressing the potential energy of the Coulomb interaction are added to the Hamiltonian operator of the system, as it is calculated in classical mechanics.
Thus, the Hamilton operator of an atom with a nuclear charge Z looks like:
j)\frac(e^2)(r_(ij))" src="http://upload.wikimedia.org/math/d/0/8/d081b99fac096b0e0c5b4290a9573794.png">.
Here m is the mass of the electron, e is its charge, is the absolute value of the radius vector j th electron, . The first term expresses the kinetic energy of electrons, the second term, the potential energy of the Coulomb interaction of electrons with the nucleus, and the third term, the potential Coulomb energy of mutual repulsion of electrons. The summation in the first and second terms is carried out over all N electrons. In the third term, the summation goes over all pairs of electrons, and each pair occurs once.
Coulomb's law from the point of view of quantum electrodynamics
According to quantum electrodynamics, the electromagnetic interaction of charged particles is carried out by the exchange of virtual photons between particles. The uncertainty principle for time and energy allows the existence of virtual photons for the time between the moments of their emission and absorption. The smaller the distance between charged particles, the less time virtual photons need to overcome this distance and, consequently, the greater the energy of virtual photons is allowed by the uncertainty principle. At small distances between charges, the uncertainty principle allows the exchange of both long-wavelength and short-wavelength photons, and at large distances, only long-wavelength photons participate in the exchange. Thus, with the help of quantum electrodynamics, one can derive Coulomb's law.
History
For the first time to investigate experimentally the law of interaction of electrically charged bodies was proposed by G. V. Richman in 1752-1753. He intended to use for this purpose the "indicator" electrometer designed by him. The implementation of this plan was prevented by the tragic death of Richman.
In 1759 F. Epinus, a professor of physics at the St. Petersburg Academy of Sciences, who took over the chair of Richmann after his death, suggested for the first time that charges should interact inversely with the square of the distance. In 1760, a brief report appeared that D. Bernoulli in Basel established a quadratic law with the help of an electrometer designed by him. In 1767, Priestley noted in his "History of Electricity" that the experience of Franklin, who discovered the absence of electric field inside a charged metal ball, could mean that "electrical attraction follows exactly the same law as gravitation, that is, the square of distance". The Scottish physicist John Robison claimed (1822) to have discovered in 1769 that balls with the same electric charge repel with a force inversely proportional to the square of the distance between them, and thus anticipated the discovery of Coulomb's law (1785).
Approximately 11 years before Coulomb, in 1771, the law of interaction of charges was experimentally discovered by G. Cavendish, but the result was not published and long time(over 100 years) remained unknown. The Cavendish manuscripts were handed over to D.K. Maxwell only in 1874 by one of Cavendish's descendants at the grand opening of the Cavendish Laboratory and published in 1879.
Coulomb himself was engaged in the study of the torsion of threads and invented the torsion balance. He discovered his law, using them to measure the forces of interaction of charged balls.
Coulomb's law, superposition principle and Maxwell's equations
Coulomb's law and the superposition principle for electric fields are completely equivalent to Maxwell's equations for electrostatics and . That is, Coulomb's law and the superposition principle for electric fields are satisfied if and only if Maxwell's equations for electrostatics are satisfied and, conversely, Maxwell's equations for electrostatics are satisfied if and only if Coulomb's law and the superposition principle are satisfied for electric fields.
Degree of accuracy of Coulomb's law
Coulomb's law is an experimentally established fact. Its validity has been repeatedly confirmed by more and more precise experiments. One of the directions of such experiments is to check whether the exponent differs r in the law of 2. To find this difference, the fact is used that if the degree is exactly equal to two, then there is no field inside the cavity in the conductor, whatever the shape of the cavity or conductor.
Experiments conducted in 1971 in the United States by E. R. Williams, D. E. Voller, and G. A. Hill showed that the exponent in Coulomb's law is 2 to within .
To test the accuracy of Coulomb's law at intraatomic distances, W. Yu. Lamb and R. Rutherford in 1947 used measurements of the relative arrangement of hydrogen energy levels. It was found that even at distances of the order of atomic 10−8 cm, the exponent in the Coulomb law differs from 2 by no more than 10−9.
The coefficient in Coulomb's law remains constant up to 15·10−6.
Corrections to Coulomb's law in quantum electrodynamics
At short distances (of the order of the Compton wavelength of an electron, ≈3.86 10−13 m, where is the electron mass, is the Planck constant, and is the speed of light), the nonlinear effects of quantum electrodynamics become significant: the virtual photon exchange is superimposed by the generation of virtual electron-positron (and also muon-antimuon and taon-antitaon) pairs, and the effect of screening also decreases (see renormalization). Both effects lead to the appearance of exponentially decreasing order terms in the expression for the potential energy of interaction of charges and, as a result, to an increase in the interaction force compared to that calculated by the Coulomb law. For example, the expression for the potential of a point charge in the CGS system, taking into account first-order radiative corrections, takes the form:
where is the Compton wavelength of the electron, is the fine structure constant, and . At distances of the order of ~10−18 m, where is the mass of the W boson, electroweak effects come into play.
In strong external electromagnetic fields, which make up a significant fraction of the vacuum breakdown field (on the order of ~1018 V/m or ~109 T, such fields are observed, for example, near certain types of neutron stars, namely magnetars), the Coulomb law is also violated due to the Delbrück scattering of exchange photons on photons of the external field and other, more complex nonlinear effects. This phenomenon reduces the Coulomb force not only on the microscale but also on the macroscale; in particular, in a strong magnetic field the Coulomb potential decreases exponentially rather than inversely with the distance.
Coulomb's law and vacuum polarization
The phenomenon of vacuum polarization in quantum electrodynamics is the formation of virtual electron-positron pairs. A cloud of electron-positron pairs shields the electric charge of an electron. The screening increases with increasing distance from the electron, as a result, the effective electric charge of the electron is a decreasing function of the distance. The effective potential created by an electron with an electric charge can be described by a dependence of the form . The effective charge depends on the distance according to the logarithmic law:
- so-called. fine structure constant ≈7.3 10−3;
- so-called. classical electron radius ≈2.8 10−13 cm.
Yuling effect
The phenomenon of the deviation of the electrostatic potential of point charges in vacuum from the value of the Coulomb's law is known as the Yuling effect, which first calculated the deviations from the Coulomb's law for the hydrogen atom. The Yuling effect corrects for the Lamb shift by 27 MHz.
Coulomb's law and superheavy nuclei
In a strong electromagnetic field near superheavy nuclei with a charge of 170" src="http://upload.wikimedia.org/math/0/d/7/0d7b5476a5437d2a99326cf04b131458.png">, a rearrangement of the vacuum occurs, similar to the usual phase transition. This leads to corrections to Coulomb's law.
The meaning of Coulomb's law in the history of science
Coulomb's law is the first open quantitative and formulated on mathematical language law for electromagnetic phenomena. With the discovery of Coulomb's law began modern science about electromagnetism.
Page 56
THE LAW OF THE COULON
Basic law of electrostatics. The concept of a point charged body.
Measurement of the force of interaction of charges using torsion balances. Coulomb's experiments
Definition of a point charge
Coulomb's law. Formulation and formula
Pendant Force
Definition of unit of charge
Coefficient in Coulomb's law
Comparison of electrostatic and gravitational forces in an atom
Equilibrium of static charges and its physical meaning(on the example of three charges)
The basic law of electrostatics is the law of interaction of two motionless point charged bodies.
It was erected by Charles Augustin Coulomb in 1785 and bears his name.
In nature, point charged bodies do not exist, but if the distance between the bodies is many times greater than their size, then neither the shape nor the size of the charged bodies significantly affect the interactions between them. In the current case, these bodies can be considered as point bodies.
The strength of the interaction of charged bodies depends on the properties of the medium between them. Experience shows that air has very little effect on the strength of this interaction, and it turns out to be almost the same as in vacuum.
Coulomb experience
The first results on measuring the force of interaction of charges were obtained in 1785 by the French scientist Charles Augustin Coulomb
A torsion balance was used to measure the force.
A small, thin, uncharged golden sphere at one end of an insulating beam suspended on an elastic silver thread was balanced at the other end of the beam by a paper disk.
By turning the rocker, it was brought into contact with the same motionless charged sphere, as a result of which its charge was divided equally between the spheres.
The diameter of the spheres was chosen to be much smaller than the distance between them in order to eliminate the effect of the size and shape of charged bodies on the measurement results.
point charge- a charged body, the size of which is much less than the distance of its possible action on other bodies.
Spheres having the same charges began to repel each other, twisting the thread. The angle of rotation was proportional to the force acting on the moving sphere.
The distance between the spheres was measured using a special calibration scale.
By discharging sphere 1 after measuring the force and connecting it again with the stationary sphere, Coulomb reduced the charge on the interacting spheres by 2,4,8, etc. once,
Coulomb's law:
The force of interaction between two motionless point charges in vacuum is directly proportional to the product of charge modules and inversely proportional to the square of the distance between them, and is directed along the straight line connecting the charges.
k is the coefficient of proportionality, depending on the choice of the system of units.
The force F12 is called the Coulomb force
The Coulomb force is central, i.e. directed along the line connecting the centers of charges.
In SI, the unit of charge is not the basic, but the derivative, and is defined using the Ampere, the basic SI unit.
Pendant - an electric charge passing through the cross section of the conductor at a current strength of 1 A in 1 s
In SI, the coefficient of proportionality in Coulomb's law for vacuum is:
k = 9*109 Nm2/Cl2
The coefficient is often written as:
e0 \u003d 8.85 * 10-12 C2 / (Nm2) - electrical constant
Coulomb's law is written in the form:
If a point charge is placed in a medium with a relative permittivity e other than vacuum, the Coulomb force will decrease by a factor of e.
For any medium except vacuum e > 1
According to Coulomb's law, two point charges of 1 C each, at a distance of 1 m in vacuum, interact with a force
From this estimate, it can be seen that a charge of 1 Coulomb is a very large quantity.
In practice, they use submultiple units - μC (10-6), μC (10-3)
1 C contains 6 * 1018 electron charges.
Using the example of the forces of interaction between an electron and a proton in a nucleus, it can be shown that the electrostatic force of interaction between particles is greater than the gravitational force by about 39 orders of magnitude. However, the electrostatic forces of interaction of macroscopic bodies (generally electrically neutral) are determined only by very small excess charges located on them, and therefore are not large in comparison with gravitational forces that depend on the mass of the bodies.
Is it possible to balance static charges?
Consider a system of two positive point charges q1 and q2.
Let's find at what point the third charge should be placed so that it is in equilibrium, and also determine the magnitude and sign of this charge.
Static equilibrium occurs when the geometric (vector) sum of the forces acting on the body is zero.
The point at which the forces acting on the third charge q3 can cancel each other is on the line between the charges.
In this case, the charge q3 can be both positive and negative. In the first case, the repulsive forces are compensated, in the second, the attractive forces.
Taking into account Coulomb's law, the static equilibrium of charges will be in the case of:
The equilibrium of the charge q3 does not depend on its value or on the sign of the charge.
When the charge q3 changes, both the attractive forces (q3 positive) and the repulsive forces (q3 negative) change equally
By solving the quadratic equation for x, it can be shown that a charge of any sign and magnitude will be in equilibrium at a point at a distance x1 from the charge q1:
Let us find out whether the position of the third charge will be stable or unstable.
(In stable equilibrium, the body, taken out of the equilibrium position, returns to it, in unstable equilibrium, it moves away from it)
With a horizontal displacement, the repulsive forces F31, F32 change due to a change in the distances between the charges, returning the charge to the equilibrium position.
With a horizontal displacement, the charge equilibrium q3 is stable.
With vertical displacement, the resultant F31, F32 pushes out q3
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In electrostatics, Coulomb's law is one of the fundamental ones. It is used in physics to determine the force of interaction between two fixed point charges or the distance between them. It is a fundamental law of nature that does not depend on any other laws. Then the shape of the real body does not affect the magnitude of the forces. In this article, we will tell plain language Coulomb's law and its application in practice.
Discovery history
Sh.O. Coulomb in 1785 for the first time experimentally proved the interactions described by the law. In his experiments, he used a special torsion balance. However, back in 1773, Cavendish proved, using the example of a spherical capacitor, that there is no electric field inside the sphere. This suggested that electrostatic forces change depending on the distance between the bodies. To be more precise - the square of the distance. Then his research was not published. Historically, this discovery was named after Coulomb, and the quantity in which the charge is measured has a similar name.
Wording
The definition of Coulomb's law is: in a vacuumF interaction of two charged bodies is directly proportional to the product of their modules and inversely proportional to the square of the distance between them.
It sounds short, but it may not be clear to everyone. In simple words: The more charge the bodies have and the closer they are to each other, the greater the force.
And vice versa: If you increase the distance between the charges - the force will become less.
The formula for Coulomb's rule looks like this:
Designation of letters: q - charge value, r - distance between them, k - coefficient, depends on the chosen system of units.
The value of the charge q can be conditionally positive or conditionally negative. This division is very conditional. When bodies come into contact, it can be transmitted from one to another. It follows that the same body can have a charge of different magnitude and sign. A point charge is such a charge or a body whose dimensions are much smaller than the distance of possible interaction.
It should be taken into account that the environment in which the charges are located affects the interaction F. Since it is almost equal in air and in vacuum, Coulomb's discovery is applicable only for these media, this is one of the conditions for applying this type of formula. As already mentioned, in the SI system, the unit of charge is Coulomb, abbreviated as Cl. It characterizes the amount of electricity per unit of time. It is a derivative of the basic SI units.
1 C = 1 A * 1 s
It should be noted that the dimension of 1 C is redundant. Due to the fact that the carriers repel each other, it is difficult to keep them in a small body, although the 1A current itself is small if it flows in a conductor. For example, in the same 100 W incandescent lamp, a current of 0.5 A flows, and in an electric heater and more than 10 A. Such a force (1 C) is approximately equal to the force acting on a body with a mass of 1 t from the side of the globe.
You may have noticed that the formula is almost the same as in the gravitational interaction, only if in Newtonian mechanics masses appear, then in electrostatics - charges.
Coulomb's formula for a dielectric medium
The coefficient, taking into account the values of the SI system, is determined in N 2 *m 2 /Cl 2. It is equal to:
In many textbooks, this coefficient can be found in the form of a fraction:
Here E 0 \u003d 8.85 * 10-12 C2 / N * m2 is an electrical constant. For a dielectric, E is added - the dielectric constant of the medium, then the Coulomb law can be used to calculate the forces of interaction of charges for vacuum and the medium.
Taking into account the influence of the dielectric, it has the form:
From here we see that the introduction of a dielectric between the bodies reduces the force F.
How are the forces directed?
Charges interact with each other depending on their polarity - the same charges repel, and the opposite (opposite) attract.
By the way, this is the main difference from a similar law of gravitational interaction, where bodies always attract. Forces directed along a line drawn between them is called the radius vector. In physics, it is denoted as r 12 and as a radius vector from the first to the second charge and vice versa. The forces are directed from the center of the charge to the opposite charge along this line if the charges are opposite, and in reverse side, if they are of the same name (two positive or two negative). In vector form:
The force applied to the first charge from the second is denoted as F 12. Then, in vector form, Coulomb's law looks like this:
To determine the force applied to the second charge, the designations F 21 and R 21 are used.
If the body has complex shape and it is large enough that at a given distance it cannot be considered a point charge, then it is divided into small sections and each section is considered as a point charge. After the geometric addition of all the resulting vectors, the resulting force is obtained. Atoms and molecules interact with each other according to the same law.
Application in practice
Coulomb's works are very important in electrostatics; in practice, they are used in a number of inventions and devices. A striking example is the lightning rod. With its help, they protect buildings and electrical installations from thunderstorms, thereby preventing fire and equipment failure. When it rains with a thunderstorm, an induced charge of large magnitude appears on the earth, they are attracted towards the cloud. It turns out that a large electric field appears on the surface of the earth. Near the tip of the lightning rod, it has a large value, as a result of which a corona discharge is ignited from the tip (from the ground, through the lightning rod to the cloud). The charge from the ground is attracted to the opposite charge of the cloud, according to Coulomb's law. The air is ionized, and the electric field strength decreases near the end of the lightning rod. Thus, the charges do not accumulate on the building, in which case the probability of a lightning strike is small. If a blow to the building occurs, then through the lightning rod all the energy will go into the ground.
In serious scientific research use the greatest construction of the 21st century - the particle accelerator. In it, the electric field does the work of increasing the energy of the particle. Considering these processes from the point of view of the impact on a point charge by a group of charges, then all the relations of the law turn out to be valid.
Useful
Charges and electricity are terms that are obligatory for those cases when the interaction of charged bodies is observed. The forces of repulsion and attraction seem to emanate from charged bodies and spread simultaneously in all directions, gradually fading away at a distance. This force was once discovered by the famous French naturalist Charles Coulomb, and the rule that charged bodies obey has since been called Coulomb's Law.
Charles Pendant
The French scientist was born in France, where he received an excellent education. He actively applied the acquired knowledge in engineering sciences and made a significant contribution to the theory of mechanisms. Coulomb is the author of works that studied the operation of windmills, the statistics of various structures, the torsion of threads under the influence external forces. One of these works helped discover the Coulomb-Amonton law, which explains friction processes.
But Charles Coulomb made the main contribution to the study of static electricity. The experiments that this French scientist conducted led him to understand one of the most fundamental laws of physics. It is to him that we owe our knowledge of the nature of the interaction of charged bodies.
background
The forces of attraction and repulsion with which electric charges act on each other are directed along the straight line connecting the charged bodies. As the distance increases, this force weakens. A century after Isaac Newton discovered his universal law of gravity, the French scientist C. Coulomb experimentally investigated the principle of interaction between charged bodies and proved that the nature of such a force is similar to the forces of gravity. Moreover, as it turned out, interacting bodies in an electric field behave in the same way as any bodies with mass in a gravitational field.
Coulomb device
The scheme of the device with which Charles Coulomb made his measurements is shown in the figure:
As you can see, in essence this design does not differ from the device that Cavendish once used to measure the value of the gravitational constant. An insulating rod suspended on a thin thread ends with a metal ball, which is given a certain electric charge. Another metal ball is approached to the ball, and then, as it approaches, the interaction force is measured by the degree of twisting of the thread.
Coulomb experiment
Coulomb suggested that the then-known Hooke's Law can be applied to the force with which the thread is twisted. The scientist compared the change in force at different distances of one ball from another and found that the interaction force changes its value inversely with the square of the distance between the balls. The pendant managed to change the values of the charged ball from q to q/2, q/4, q/8 and so on. With each change in charge, the interaction force proportionally changed its value. So, gradually, a rule was formulated, which was later called "Coulomb's Law".
Definition
Experimentally, the French scientist proved that the forces with which two charged bodies interact are proportional to the product of their charges and inversely proportional to the square of the distance between the charges. This statement is Coulomb's law. In mathematical form, it can be expressed as follows:
In this expression:
- q is the amount of charge;
- d is the distance between charged bodies;
- k is the electrical constant.
The value of the electrical constant largely depends on the choice of the unit of measurement. AT modern system the magnitude of the electric charge is measured in coulombs, and the electrical constant, respectively, in newton × m 2 / coulomb 2.
Recent measurements have shown that this coefficient should take into account the dielectric constant of the medium in which the experiment is carried out. Now the value is shown as the ratio k=k 1 /e, where k 1 is the electrical constant already familiar to us, and is not an indicator of the permittivity. Under vacuum conditions, this value is equal to unity.
Conclusions from Coulomb's law
The scientist experimented with different charges, testing the interaction between bodies with different charges. Of course, he could not measure the electric charge in any units - he lacked neither knowledge nor appropriate instruments. Charles Coulomb was able to separate the projectile by touching the charged ball uncharged. So he received fractional values of the initial charge. A number of experiments have shown that the electric charge is conserved, the exchange takes place without an increase or decrease in the amount of charge. This fundamental principle formed the basis of the law of conservation of electric charge. At present, it has been proved that this law is observed both in the microcosm of elementary particles and in the macrocosm of stars and galaxies.
Conditions necessary for the fulfillment of Coulomb's law
In order for the law to be fulfilled with greater accuracy, the following conditions must be met:
- Charges must be point. In other words, the distance between the observed charged bodies must be much larger than their sizes. If charged bodies are spherical, then we can assume that all the charge is at a point that is the center of the sphere.
- The bodies to be measured must be stationary. Otherwise, the moving charge will be influenced by numerous third-party factors, for example, the Lorentz force, which gives the charged body additional acceleration. As well as the magnetic field of a moving charged body.
- Observed bodies must be in a vacuum to avoid the effects of flows air masses on the results of the observations.
Coulomb's law and quantum electrodynamics
From the point of view of quantum electrodynamics, the interaction of charged bodies occurs through the exchange of virtual photons. The existence of such unobservable particles and zero mass but not zero charge is indirectly supported by the uncertainty principle. According to this principle, a virtual photon can exist between the moments of emission of such a particle and its absorption. The smaller the distance between the bodies, the less time the photon spends on the passage of the path, therefore, the greater the energy of the emitted photons. At a small distance between the observed charges, the uncertainty principle allows the exchange of both short-wave and long-wave particles, and at large distances, short-wave photons do not participate in the exchange.
Are there limits to the application of Coulomb's law
Coulomb's law fully explains the behavior of two point charges in a vacuum. But when it comes to real bodies, one should take into account the volumetric dimensions of charged bodies and the characteristics of the medium in which the observation is made. For example, some researchers have observed that a body that carries a small charge and is forcibly brought into the electric field of another object with a large charge begins to be attracted to this charge. In this case, the statement that similarly charged bodies repel each other fails, and another explanation for the observed phenomenon should be sought. Most likely, we are not talking about a violation of Coulomb's law or the principle of conservation of electric charge - it is possible that we are observing phenomena that have not been fully studied to the end, which science will be able to explain a little later.
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