A unit of measure for electric charge. Pendant. Relationship with other physical quantities. (10+)

A unit of measure for electric charge. Pendant (Coulomb)

The material is an explanation and addition to the article:
Units of measurement of physical quantities in radio electronics
Units of measurement and ratios of physical quantities used in radio engineering.

The electric charge of a body is the difference between the number of charged particles of one polarity and the other polarity in this body (with some assumptions). Electric charge can have positive or negative polarity. Bodies with a charge of the same polarity repel each other, while those with a charge of different polarity attract.

Electric charge is measured in Coulomb. Designation K. International designation C. The charge in formulas is usually denoted by the letter Q.

The electric charge of an electron is about 1.602176E-19 Coulomb, has a negative sign. The proton charge is equal to the same value, but positive. In matter, usually electrons and protons are present in equal amounts, so that the total charge is zero. In some cases, the number of electrons can increase, then we say that the body is negatively charged, or decrease, then the body is positively charged.

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As a result of long observations, scientists have found that oppositely charged bodies attract, and vice versa charged bodies repel each other. This means that interaction forces arise between bodies. The French physicist C. Coulomb experimentally investigated the patterns of interaction of metal balls and found that the force of interaction between two point electric charges will be directly proportional to the product of these charges and inversely proportional to the square of the distance between them:

Where k is a coefficient of proportionality, depending on the choice of units of measurements of physical quantities that are included in the formula, as well as on the environment in which the electric charges q 1 and q 2 are located. r is the distance between them.

From this we can conclude that Coulomb's law will be valid only for point charges, that is, for such bodies, the dimensions of which can be completely neglected compared to the distances between them.

In vector form, Coulomb's law will look like:

Where q 1 and q 2 are charges, and r is the radius vector connecting them; r = |r|.

Forces acting on charges are called central forces. They are directed along a straight line connecting these charges, and the force acting from the charge q 2 on the charge q 1 is equal to the force acting from the charge q 1 on the charge q 2, and opposite in sign.

To measure electrical quantities, two number systems can be used - the SI system (basic) and sometimes the CGS system can be used.

In the SI system, one of the main electrical quantities is the unit of current strength - ampere (A), then the unit of electric charge will be its derivative (expressed in terms of the unit of current strength). The SI unit of charge is the pendant. 1 pendant (C) is the amount of "electricity" passing through the cross section of the conductor in 1 s at a current of 1 A, that is, 1 C = 1 A s.

The coefficient k in formula 1a) in SI is taken equal to:

And Coulomb's law can be written in the so-called "rationalized" form:

Many equations describing magnetic and electrical phenomena contain the factor 4π. However, if this factor is introduced into the denominator of Coulomb's law, then it will disappear from most formulas of magnetism and electricity, which are very often used in practical calculations. This form of writing the equation is called rationalized.

The value of ε 0 in this formula is an electrical constant.

The basic units of the CGS system are the CGS mechanical units (gram, second, centimeter). New basic units in addition to the above three are not introduced in the CGS system. The coefficient k in formula (1) is assumed to be unity and dimensionless. Accordingly, Coulomb's law in a non-rationalized form will have the form:

In the CGS system, force is measured in dynes: 1 dyne \u003d 1 g cm / s 2, and the distance is in centimeters. Suppose that q \u003d q 1 \u003d q 2, then from formula (4) we get:

If r = 1 cm, and F = 1 dyne, then this formula implies that in the CGS system, a point charge is taken as a unit of charge, which (in vacuum) acts on an equal charge located at a distance of 1 cm from it, with a force of 1 din. Such a unit of charge is called the absolute electrostatic unit of the amount of electricity (charge) and is denoted by CGS q. Its dimension:

To calculate the value of ε 0 , let's compare the expressions for the Coulomb's law written in the SI and CGS systems. Two point charges of 1 C each, which are at a distance of 1 m from each other, will interact with a force (according to formula 3):

In the GHS, this force will be equal to:

The strength of the interaction between two charged particles depends on the environment in which they are located. To characterize the electrical properties of various media, the concept of relative permittivity ε was introduced.

The value of ε is a different value for different substances - for ferroelectrics, its value lies in the range of 200 - 100,000, for crystalline substances from 4 to 3000, for glass from 3 to 20, for polar liquids from 3 to 81, for non-polar liquids from 1, 8 to 2.3; for gases from 1.0002 to 1.006.

The dielectric constant (relative) also depends on the ambient temperature.

If we take into account the permittivity of the medium in which the charges are placed, in SI Coulomb's law takes the form:

The dielectric permittivity ε is a dimensionless quantity and it does not depend on the choice of units of measurement and for vacuum it is considered equal to ε = 1. Then for vacuum the Coulomb law takes the form:

Dividing expression (6) by (5) we get:

Accordingly, the relative permittivity ε shows how many times the interaction force between point charges in some medium that are at a distance r relative to each other is less than in vacuum, at the same distance.

For the division of electricity and magnetism, the CGS system is sometimes called the Gaussian system. Before the advent of the CGS system, the CGSE (CGS electric) systems were in operation for measuring electrical quantities and CGSM (CGS magnetic) for measuring magnetic quantities. In the first equal unit, the electric constant ε 0 was taken, and the second, the magnetic constant μ 0 .

In the CGS system, the formulas of electrostatics coincide with the corresponding formulas of the CGSE, and the formulas of magnetism, provided that they contain only magnetic quantities, with the corresponding formulas in the CGSM.

But if the equation simultaneously contains both magnetic and electrical quantities, then this equation, written in the Gauss system, will differ from the same equation, but written in the CGSM or CGSE system by the factor 1/s or 1/s 2. The value c is equal to the speed of light (c = 3·10 10 cm/s) is called the electrodynamic constant.

Coulomb's law in the CGS system will have the form:

Example

On two absolutely identical drops of oil, one electron is missing. The force of Newtonian attraction is balanced by the force of Coulomb repulsion. It is necessary to determine the radii of the droplets if the distance between them significantly exceeds their linear dimensions.

Decision

Since the distance between the drops r is much larger than their linear dimensions, the drops can be taken as point charges, and then the Coulomb repulsion force will be equal to:

Where e is the positive charge of the oil drop, equal to the charge of the electron.

The force of Newtonian attraction can be expressed by the formula:

Where m is the mass of the drop and γ is the gravitational constant. According to the condition of the problem F k \u003d F n, therefore:

The mass of the drop is expressed in terms of the product of the density ρ and the volume V, that is, m = ρV, and the volume of the drop of radius R is equal to V = (4/3)πR 3 , from which we obtain:

In this formula, the constants π, ε 0 , γ are known; ε = 1; also known is the electron charge e \u003d 1.6 10 -19 C and the oil density ρ \u003d 780 kg / m 3 (reference data). Substituting the numerical values ​​into the formula, we get the result: R = 0.363 10 -7 m.

« Physics - Grade 10 "

What interactions are called electromagnetic?
What is the interaction of charges?

Let's start studying the quantitative laws of electromagnetic interactions. The basic law of electrostatics is the law of the interaction of two motionless point charged bodies.

The fundamental law of electrostatics was experimentally established by Charles Coulomb in 1785 and bears his name.

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.

Recall that the law of universal gravitation is also formulated for bodies, which can be considered material points.

Charged bodies, the size and shape of which can be neglected during their interaction, are called point charges.

The force of interaction of charged bodies depends on the properties of the medium between the charged bodies. For the time being, we will assume that the interaction takes place in a vacuum. Experience shows that air has very little effect on the force of interaction of charged bodies, it turns out to be almost the same as in vacuum.

Coulomb's experiments.

The idea of ​​Coulomb's experiments is similar to the idea of ​​Cavendish's experience in determining the gravitational constant. The discovery of the law of interaction of electric charges was facilitated by the fact that these forces turned out to be large and due to this it was not necessary to use especially sensitive equipment, as when testing the law of universal gravitation in terrestrial conditions. With the help of torsion balances, it was possible to establish how motionless charged bodies interact with each other.

Torsion balances consist of a glass rod suspended on a thin elastic wire (Fig. 14.3). A small metal ball a is fixed at one end of the stick, and a counterweight c at the other. Another metal ball b is fixed motionless on the rod, which, in turn, is attached to the balance cover.

When the balls of the same charges are imparted, they begin to repel each other. To keep them at a fixed distance, the elastic wire must be twisted through a certain angle until the resulting elastic force compensates for the Coulomb repulsive force of the balls. The angle of twisting of the wire determines the force of interaction of the balls.

Torsion balances made it possible to study the dependence of the interaction force of charged balls on the values ​​of the charges and on the distance between them. They knew how to measure force and distance at that time. The only difficulty was connected with the charge for the measurement of which there were not even units. The pendant found a simple way to change the charge of one of the balls by 2, 4 or more times by connecting it with the same uncharged ball. In this case, the charge was distributed equally between the balls, which reduced the investigated charge in a certain respect. The new value of the interaction force with a new charge was determined experimentally.

Coulomb's law.

Coulomb's experiments led to the establishment of a law strikingly reminiscent of the law of universal gravitation.

The force of interaction of two stationary point charges in vacuum is directly proportional to the product of charge moduli and inversely proportional to the square of the distance between them.

The force of interaction of charges is called Coulomb force.

If we designate the charge modules as |q 1 and |q 2 |, and the distance between them as r, then Coulomb's law can be written in the following form:

where k is the coefficient of proportionality, numerically equal to the force of interaction of unit charges at a distance equal to a unit of length. Its value depends on the choice of the system of units.

The law of universal gravitation has the same form (14.2), but instead of charge, the law of gravitation includes masses, and the role of the coefficient k is played by the gravitational constant.

It is easy to find that two charged balls suspended on strings either attract each other or repel each other. Hence it follows that the forces of interaction of two fixed point charges are directed along the straight line connecting these charges(Fig. 14.4).

Such forces are called central. According to Newton's third law 1.2 = - 2.1.

Unit of electric charge.

The choice of the unit of charge, as well as other physical quantities, is arbitrary. It would be natural to take the charge of an electron as a unit, which is done in atomic physics, but this charge is too small, and therefore it is not always convenient to use it as a unit of charge.

In the International System of Units (SI), the charge unit is not the main one, but a derivative, and the standard for it is not introduced. Along with the meter, second and kilogram, the SI introduced the basic unit for electrical quantities - the unit of current - ampere. The reference value of the ampere is set using the magnetic interactions of the currents.

Unit of charge in SI - pendant set using the unit of current.

One pendant (1 C) is a charge that passes in 1 s through the cross section of the conductor at a current of 1 A: 1 C = 1 A 1 s.

The unit of the coefficient k in Coulomb's law when written in SI units is N m 2 / Cl 2, since according to formula (14.2) we have

where the force of interaction of charges is expressed in newtons, the distance is in meters, the charge is in coulombs. The numerical value of this coefficient can be determined experimentally. To do this, it is necessary to measure the force of interaction F between two known charges |q 1 | and |q 2 |, located at a given distance r, and substitute these values ​​into formula (14.3). The resulting value of k will be:

k \u003d 9 10 9 N m 2 / Cl 2. (14.4)

A charge of 1 C is very large. The interaction force of two point charges, 1 C each, located at a distance of 1 km from each other, is slightly less than the force with which the globe attracts a load of 1 ton. Therefore, tell a small body (of the order of several meters in size) a charge of 1 C is impossible.

Repelling each other, charged particles cannot stay on the body. There are no other forces capable of compensating the Coulomb repulsion under the given conditions in nature.

But in a conductor that is generally neutral, it is not difficult to set in motion a charge of 1 C. Indeed, in a conventional light bulb with a power of 200 W at a voltage of 220 V, the current strength is slightly less than 1 A. At the same time, a charge almost equal to 1 C passes through the cross section of the conductor in 1 s.

Instead of the coefficient k, another coefficient is often used, which is called electric constant ε 0. It is related to the coefficient k by the following relation:

Coulomb's law in this case has the form

If the charges interact in the medium, then the interaction force decreases:

where ε - the dielectric constant medium, showing how many times the force of interaction of charges in the medium is less than in vacuum.

The minimum charge that exists in nature is the charge of elementary particles. In SI units, the modulus of this charge is:

e \u003d 1.6 10 -19 C. (14.5)

The charge that can be imparted to the body is always a multiple of the minimum charge:

where N is an integer. When the charge of the body is significantly greater in modulus of the minimum charge, then it makes no sense to check the multiplicity, however, when it comes to the charge of particles, atomic nuclei, their charge must always be equal to an integer number of electron charge modules.

Let there be two charged macroscopic bodies, the sizes of which are negligibly small in comparison with the distance between them. In this case, each body can be considered a material point or "point charge".

The French physicist C. Coulomb (1736–1806) experimentally established the law that bears his name ( Coulomb's law) (Fig. 1.5):

Rice. 1.5. C. Coulomb (1736–1806) - French engineer and physicist

In a vacuum, the force of interaction between two fixed point charges is proportional to the magnitude of each of the charges, inversely proportional to the square of the distance between them, and is directed along a straight line connecting these charges:

On fig. 1.6 shows the electric repulsive forces that arise between two like point charges.

Rice. 1.6. Electric repulsive forces between two like point charges

Recall that , where and are the radius vectors of the first and second charges, so the force acting on the second charge as a result of its electrostatic - "Coulomb" interaction with the first charge can be rewritten in the following "unfolded" form

We note the following rule, which is convenient in solving problems: if the first index of the force is the number of that charge, on which this force acts, and the second is the number of that charge, which creates this force, then the observance of the same order of indices on the right side of the formula automatically ensures the correct direction of the force - corresponding to the sign of the product of the charges: - repulsion and - attraction, while the coefficient is always.

To measure the forces acting between point charges, an instrument created by Coulomb was used, called torsion balances(Fig. 1.7, 1.8).

Rice. 1.7. Torsion balances of Sh. Coulomb (drawing from a work of 1785). The force acting between the charged balls a and b was measured

Rice. 1.8. Torsional scales of Sh. Coulomb (suspension point)

A light rocker is suspended on a thin elastic thread, at one end of which a metal ball is fixed, and at the other - a counterweight. Next to the first ball, you can place another identical motionless ball. The glass cylinder protects sensitive parts of the instrument from air movement.

To establish the dependence of the electrostatic interaction force on the distance between the charges, arbitrary charges are imparted to the balls by touching them with a third charged ball mounted on a dielectric handle. According to the angle of twisting of the elastic thread, one can measure the repulsive force of like-charged balls, and on the scale of the device - the distance between them.

It must be said that Coulomb was not the first scientist to establish the law of interaction of charges, which now bears his name: 30 years before him, B. Franklin came to the same conclusion. Moreover, the accuracy of Coulomb's measurements was inferior to the accuracy of earlier experiments (G. Cavendish).

To introduce a quantitative measure for determining the accuracy of measurements, suppose that in fact the force of interaction of charges is not the inverse of the square of the distance between them, but of some other degree:

None of the scientists will undertake to assert that d= 0 exactly. The correct conclusion should sound like this: experiments have shown that d less than...

The results of some of these experiments are shown in Table 1.

Table 1.

Results of direct experiments to test Coulomb's law

Charles Coulomb himself tested the inverse square law to within a few percent. The table shows the results of direct laboratory experiments. Indirect data based on observations of magnetic fields in outer space lead to even stronger restrictions on the value d. Thus, Coulomb's law can be considered a reliably established fact.

The SI unit of current ( ampere) is basic, hence the unit of charge q turns out to be a derivative. As we will see later, the current I is defined as the ratio of the charge flowing through the cross section of the conductor in time to this time:

From this it can be seen that the direct current strength is numerically equal to the charge flowing through the cross section of the conductor per unit time, respectively:

The coefficient of proportionality in Coulomb's law is written as:

With this form of notation, the value of the quantity follows from the experiment, which is usually called electrical constant. The approximate numerical value of the electrical constant is as follows:

Since it most often enters equations as a combination

we give the numerical value of the coefficient itself

As in the case of an elementary charge, the numerical value of the electric constant is determined experimentally with high accuracy:

The pendant is too large a unit to be used in practice. For example, two charges of 1 C each, located in vacuum at a distance of 100 m from each other, repel each other with a force

For comparison: with such a force, a body of mass

This is approximately the mass of a freight railway car, for example, with coal.

Principle of superposition of fields

The principle of superposition is a statement according to which the resulting effect of a complex impact process is the sum of the effects caused by each impact separately, provided that the latter do not mutually influence each other (Physical Encyclopedic Dictionary, Moscow, "Soviet Encyclopedia", 1983, p. .731). It has been experimentally established that the principle of superposition is valid for the electromagnetic interaction considered here.

In the case of the interaction of charged bodies, the principle of superposition manifests itself as follows: the force with which a given system of charges acts on a certain point charge is equal to the vector sum of the forces with which each of the charges of the system acts on it.

Let's explain this with a simple example. Let there be two charged bodies acting on the third with forces and respectively. Then the system of these two bodies - the first and the second - acts on the third body with the force

This rule is true for any charged bodies, not only for point charges. The forces of interaction between two arbitrary systems of point charges are calculated in Appendix 1 at the end of this chapter.

It follows from this that the electric field of a system of charges is determined by the vector sum of the field strengths created by the individual charges of the system, i.e.

The addition of electric field strengths according to the vector addition rule expresses the so-called superposition principle(independent superposition) of electric fields. The physical meaning of this property is that the electrostatic field is created only by charges at rest. This means that the fields of different charges "do not interfere" with each other, and therefore the total field of the system of charges can be calculated as the vector sum of the fields from each of them separately.

Since the elementary charge is very small, and macroscopic bodies contain a very large number of elementary charges, the distribution of charges over such bodies can in most cases be considered continuous. In order to describe exactly how the charge is distributed (uniformly, inhomogeneously, where there are more charges, where there are fewer, etc.) the charge over the body, we introduce the charge densities of the following three types:

· bulk densitycharge :

where dV- physically infinitesimal volume element;

· surface charge density :

where dS- physically infinitesimal surface element;

· linear charge density:

where is a physically infinitesimal element of the line length.

Here, everywhere is the charge of the considered physically infinitesimal element (volume, surface area, line segment). Here and below, a physically infinitely small section of a body is understood to mean such a section of it, which, on the one hand, is so small that, under the conditions of a given problem, it can be considered a material point, and, on the other hand, it is so large that the discreteness of the charge (see . ratio) of this section can be neglected.

General expressions for the interaction forces of systems of continuously distributed charges are given in Appendix 2 at the end of the chapter.

Example 1 An electric charge of 50 nC is uniformly distributed over a thin rod 15 cm long. On the continuation of the axis of the rod at a distance of 10 cm from its nearest end, there is a point charge of 100 nC (Fig. 1.9). Determine the force of interaction between a charged rod and a point charge.

Rice. 1.9. Interaction of a charged rod with a point charge

Decision. In this problem, the force F cannot be determined by writing the Coulomb law in the form or (1.3). In fact, what is the distance between the rod and the charge: r, r + a/2, r + a? Since, according to the conditions of the problem, we have no right to assume that a << r, the application of Coulomb's law in its original formulation that is valid only for point charges is impossible, it is necessary to use the standard method for such situations, which is as follows.

If the force of interaction of point bodies is known (for example, Coulomb's law) and it is necessary to find the force of interaction of extended bodies (for example, to calculate the force of interaction of two charged bodies of finite size), then it is necessary to divide these bodies into physically infinitely small sections, write for each pair of such "point » sections, the ratio known to them and, using the principle of superposition, sum (integrate) over all pairs of these sections.

It is always useful, if not necessary, to analyze the symmetry of the problem before proceeding with the specification and execution of the calculation. From a practical point of view, such an analysis is useful in that, as a rule, with a sufficiently high symmetry of the problem, it sharply reduces the number of quantities that need to be calculated, since it turns out that many of them are equal to zero.

Let's divide the rod into infinitely small segments of length , the distance from the left end of such a segment to the point charge is equal to .

The uniformity of the charge distribution over the rod means that the linear charge density is constant and equal to

Therefore, the charge of the segment is , whence, in accordance with Coulomb's law, the force acting on pinpoint charge q as a result of his interaction with pinpoint charge is equal to

As a result of interaction pinpoint charge q at all rod, a force will act on it

Substituting here the numerical values, for the modulus of force we obtain:

It can be seen from (1.5) that when , when the rod can be considered a material point, the expression for the interaction force of the charge and the rod, as it should be, takes the usual form of the Coulomb law for the interaction force of two point charges:

Example 2 A ring of radius carries a uniformly distributed charge. What is the force of interaction of the ring with a point charge q located on the axis of the ring at a distance from its center (Fig. 1.10).

Decision. According to the condition, the charge is uniformly distributed on the ring with radius . Dividing by the circumference, we get the linear charge density on the ring Select an element of length on the ring. Its charge is .

Rice. 1.10. Interactions of a ring with a point charge

At the point q this element creates an electric field

We are only interested in the longitudinal component of the field, because when summing the contribution from all elements of the ring, only it is nonzero:

Integrating over, we find the electric field on the axis of the ring at a distance from its center:

From here we find the desired force of interaction of the ring with the charge q:

Let's discuss the result. At large distances to the ring, the radius of the ring under the sign of the radical can be neglected, and we obtain an approximate expression

This is not surprising, since at large distances the ring looks like a point charge and the force of interaction is given by the usual Coulomb's law. At short distances, the situation changes dramatically. So, when a test charge q is placed in the center of the ring, the interaction force is zero. This is also not surprising: in this case, the charge q is attracted with equal force by all elements of the ring, and the action of all these forces is mutually compensated.

Since at and at the electric field is equal to zero, somewhere at an intermediate value, the electric field of the ring is maximum. Let's find this point by differentiating the expression for tension E by distance

Equating the derivative to zero, we find the point where the field is maximum. It is equal at this point

Example 3 Two mutually perpendicular infinitely long threads carrying uniformly distributed charges with linear densities and are at a distance a from each other (Fig. 1.11). How does the force of interaction between threads depend on the distance a?

Decision. Let us first discuss the solution of this problem by the method of dimensional analysis. The strength of the interaction between the threads may depend on the charge densities on them, the distance between the threads and the electrical constant, that is, the desired formula has the form:

where is a dimensionless constant (number). Note that due to the symmetrical arrangement of the filaments, the charge densities on them can only enter in a symmetrical way, in the same degrees. The dimensions of the quantities included here in SI are known:

Rice. 1.11. Interaction of two mutually perpendicular infinitely long threads

In comparison with mechanics, a new quantity has appeared here - the dimension of electric charge. Combining the two previous formulas, we get the equation for the dimensions:

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1 coulomb [C] = 0.0166666666666667 ampere-minute [A min]

Initial value

Converted value

coulomb megacoulomb kilocoulomb millicoulomb microcoulomb nanocoulomb picocoulomb abcoulomb unit of charge CGSM statcoulomb CGSE unit of charge franklin ampere-hour milliamp-hour ampere-minute ampere-second faraday (unit of charge) elementary electric charge

More about electric charge

General information

Surprisingly, we are exposed to static electricity on a daily basis - when petting our beloved cat, combing our hair or pulling on a synthetic sweater. So we unwittingly become generators of static electricity. We literally bathe in it, because we live in a strong electrostatic field of the Earth. This field arises due to the fact that it is surrounded by the ionosphere, the upper layer of the atmosphere is an electrically conductive layer. The ionosphere was formed under the action of cosmic radiation and has its own charge. While doing everyday things like heating food, we don’t think at all that we are using static electricity by turning the gas supply valve on an auto-ignition burner or bringing an electric lighter to it.

Examples of static electricity

From childhood, we are instinctively afraid of thunder, although in itself it is absolutely safe - just an acoustic consequence of a formidable lightning strike, which is caused by atmospheric static electricity. The sailors of the times of the sailing fleet fell into awe, watching the lights of St. Elmo on their masts, which are also a manifestation of atmospheric static electricity. People endowed the supreme gods of ancient religions with an inalienable attribute in the form of lightning, whether it be the Greek Zeus, the Roman Jupiter, the Scandinavian Thor or the Russian Perun.

Centuries have passed since people first began to be interested in electricity, and sometimes we don’t even suspect that scientists, having drawn profound conclusions from the study of static electricity, are saving us from the horrors of fires and explosions. We tamed electrostatics by aiming lightning rods into the sky and equipping fuel trucks with grounding devices that allow electrostatic charges to safely escape into the ground. And, nevertheless, static electricity continues to misbehave, interfering with the reception of radio signals - after all, up to 2000 thunderstorms are raging on Earth at the same time, which generate up to 50 lightning discharges every second.

People have been studying static electricity since time immemorial; we owe even the term "electron" to the ancient Greeks, although they meant something different by this - that is how they called amber, which was perfectly electrified during friction (other - Greek ἤλεκτρον - amber). Unfortunately, the science of static electricity has not been without casualties - the Russian scientist Georg Wilhelm Richman was killed during an experiment by lightning, which is the most formidable manifestation of atmospheric static electricity.

Static electricity and weather

In the first approximation, the mechanism of formation of charges of a thundercloud is in many respects similar to the mechanism of electrification of a comb - in it, electrification by friction occurs in exactly the same way. Ice particles, formed from small droplets of water, cooled due to the transfer of ascending air currents to the upper, colder part of the cloud, collide with each other. Larger pieces of ice are charged negatively, while smaller ones are positively charged. Due to the difference in weight, the redistribution of ice floes in the cloud occurs: large, heavier ones sink to the bottom of the cloud, and lighter, smaller ice floes gather in the upper part of the thundercloud. Although the entire cloud as a whole remains neutral, the lower part of the cloud receives a negative charge, while the upper part receives a positive charge.

Like an electrified comb that attracts a balloon due to the induction of an opposite charge on its side closest to the comb, a thundercloud induces a positive charge on the surface of the Earth. As the thundercloud develops, the charges increase, while the field strength between them increases, and when the field strength exceeds the critical value for these weather conditions, an electrical breakdown of the air occurs - a lightning discharge.

Mankind is indebted to Benjamin Franklin - later President of the Supreme Executive Council of Pennsylvania and the first Postmaster General of the United States - for the invention of a lightning rod (it would be more accurate to call it a lightning rod), which forever saved the population of the Earth from fires caused by lightning in buildings. By the way, Franklin did not patent his invention, making it available to all mankind.

Lightning did not always bring only destruction - the Ural miners determined the location of iron and copper ores precisely by the frequency of lightning strikes at certain points in the area.

Among the scientists who devoted their time to studying the phenomena of electrostatics, it is necessary to mention the Englishman Michael Faraday, later one of the founders of electrodynamics, and the Dutchman Peter van Muschenbroek, the inventor of the prototype of the electric capacitor - the famous Leyden jar.

Watching DTM, IndyCar or Formula 1 races, we do not even suspect that mechanics are calling pilots to change tires to rain, based on weather radar data. And these data, in turn, are based precisely on the electrical characteristics of the approaching thunderclouds.

Static electricity is our friend and enemy at the same time: radio engineers dislike it, pulling on grounding bracelets when repairing burnt circuit boards as a result of a nearby lightning strike - in this case, as a rule, the input stages of the equipment fail. With faulty grounding equipment, it can cause severe man-made disasters with tragic consequences - fires and explosions of entire factories.

Static electricity in medicine

Nevertheless, it comes to the aid of people with heart rhythm disturbances caused by chaotic convulsive contractions of the patient's heart. Its normal operation is restored by passing a small electrostatic discharge using a device called a defibrillator. The scene of the return of the patient from the other world with the help of a defibrillator is a kind of classic for a movie of a certain genre. It should be noted, however, that movies traditionally show a monitor with no heartbeat signal and an ominous straight line, although in fact, the use of a defibrillator does not help if the patient's heart has stopped.

Other examples

It would be useful to recall the need for metallization of aircraft to protect against static electricity, that is, the connection of all metal parts of the aircraft, including the engine, into one electrically integral structure. At the tips of the entire tail of the aircraft, static dischargers are installed to drain static electricity that accumulates during flight due to air friction against the aircraft body. These measures are necessary to protect against interference caused by the discharge of static electricity and to ensure the reliable operation of on-board electronic equipment.

Electrostatics plays a certain role in introducing students to the "Electricity" section - perhaps none of the sections of physics knows more spectacular experiments - here you have hair standing on end, and the pursuit of a balloon for a comb, and the mysterious glow of fluorescent lamps without any connection wires! But this effect of the glow of gas-filled appliances saves the lives of electricians who deal with high voltage in modern power lines and distribution networks.

And most importantly, scientists have come to the conclusion that we probably owe the appearance of life on Earth to static electricity, or rather its discharges in the form of lightning. In the course of experiments in the middle of the last century, with the passage of electrical discharges through a mixture of gases, close in composition to the primary composition of the Earth's atmosphere, one of the amino acids was obtained, which is the "brick" of our life.

To tame electrostatics, it is very important to know the potential difference or electrical voltage, for the measurement of which instruments called voltmeters were invented. The 19th-century Italian scientist Alessandro Volta introduced the concept of electrical voltage, after whom this unit is named. At one time, galvanometers were used to measure electrostatic voltage, named after Volta's compatriot Luigi Galvani. Unfortunately, these devices of the electrodynamic type introduced distortions into the measurements.

The study of static electricity

Scientists began to systematically study the nature of electrostatics from the time of the work of the 18th century French scientist Charles Augustin de Coulomb. In particular, he introduced the concept of electric charge and discovered the law of interaction of charges. The unit of measure for the amount of electricity, the coulomb (Cl), is named after him. True, for the sake of historical justice, it should be noted that years earlier the English scientist Lord Henry Cavendish was engaged in this; unfortunately, he wrote to the table and his works were published by the heirs only 100 years later.

The work of predecessors devoted to the laws of electrical interactions enabled the physicists George Green, Carl Friedrich Gauss and Simeon Denis Poisson to create a mathematically elegant theory that we still use today. The main principle in electrostatics is the postulate of an electron - an elementary particle that is part of any atom and is easily separated from it under the influence of external forces. In addition, there are postulates about the repulsion of like charges and the attraction of unlike charges.

Electricity measurement

One of the first measuring instruments was the simplest electroscope, invented by the English priest and physicist Abraham Bennett - two sheets of gold electrically conductive foil placed in a glass container. Since then, measuring instruments have evolved significantly - and now they can measure the difference in units of nanocoulombs. Using extremely precise physical instruments, Russian scientist Abram Ioffe and American physicist Robert Andrews Milliken were able to measure the electric charge of an electron.

Nowadays, with the development of digital technologies, ultra-sensitive and high-precision devices with unique characteristics have appeared, which, due to the high input resistance, almost do not introduce distortions into the measurements. In addition to measuring voltage, such devices make it possible to measure other important characteristics of electrical circuits, such as ohmic resistance and flowing current in a wide measurement range. The most advanced instruments, called multimeters or, in professional jargon, testers, because of their versatility, can also measure AC frequency, capacitor capacitance and test transistors and even measure temperature.

As a rule, modern devices have built-in protection that does not allow the device to be damaged if used incorrectly. They are compact, easy to handle and completely safe to operate - each one goes through a series of precision tests, is tested under heavy duty conditions and earns a well-deserved safety certificate.

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