The most electrically conductive metal in the world
The value of metals is directly determined by their chemical and physical properties. In the case of an indicator such as electrical conductivity, this relationship is not so straightforward. The most electrically conductive metal, when measured at room temperature (+20 °C), is silver. But high cost limits the use of silver parts in electrical engineering and microelectronics. Silver elements in such devices are used only if economically feasible.
Physical meaning of conductivity
The use of metal conductors has a long history. Scientists and engineers working in fields of science and technology that use electricity have long decided on materials for wires, terminals, contacts, printed circuit boards, etc. A physical quantity called electrical conductivity helps determine the most electrically conductive metal in the world.
The concept of conductivity is the inverse of electrical resistance. The quantification of conductivity is related to the unit of resistance, which is measured in Ohms in the International System of Units (SI). The SI unit of electrical conductivity is siemens. The Russian designation for this unit is Cm, the international designation is S. An electrical conductivity of 1 Cm has a section of an electrical network with a resistance of 1 Ohm.
Conductivity
The measure of a substance's ability to conduct electric current is called electrical conductivity. The most electrically conductive metal has the highest similar indicator. This characteristic can be determined for any substance or environment instrumentally and has a numerical expression. The specific electrical conductivity of a cylindrical conductor of unit length and unit cross-sectional area is related to the resistivity of this conductor.
The system unit for conductivity is siemens per meter – S/m. To find out which metal is the most electrically conductive metal in the world, it is enough to compare their experimentally determined conductivities. You can determine the resistivity using a special device - a microohmmeter. These characteristics are inversely dependent.
Conductivity of metals
The very concept of electric current as a directed flow of charged particles seems more harmonious for substances based on crystal lattices characteristic of metals. Charge carriers when an electric current occurs in metals are free electrons, and not ions, as is the case in liquid media. It has been experimentally established that when a current occurs in metals, there is no transfer of particles of matter between the conductors.
Metallic substances differ from others by having looser bonds at the atomic level. The internal structure of metals is characterized by the presence of a large number of “lonely” electrons. which, at the slightest influence of electromagnetic forces, form a directed flow.
Therefore, it is not for nothing that metals are the best conductors of electric current, and it is precisely such molecular interactions that distinguish the most electrically conductive metal.
Another specific property of metals—high thermal conductivity—is based on the structural features of the crystal lattice of metals.
Top best conductors - metals
4 metals that are of practical importance for their use as electrical conductors are distributed in the following order relative to the value of specific conductivity, measured in S/m:
- Silver - 62,500,000.
- Copper – 59,500,000.
- Gold – 45,500,000.
- Aluminum - 38,000,000.
It can be seen that the most electrically conductive metal is silver. But like gold, it is used to organize the electrical network only in special specific cases. The reason is high cost.
But copper and aluminum are the most common option for electrical appliances and cable products due to their low resistance to electric current and affordability. Other metals are rarely used as conductors.
Factors affecting the conductivity of metals
Even the most electrically conductive metal reduces its conductivity if it contains other additives and impurities. Alloys have a different crystal lattice structure than “pure” metals. It is characterized by a violation of symmetry, cracks and other defects. Conductivity also decreases with increasing ambient temperature.
The increased resistance inherent in alloys is used in heating elements. It is no coincidence that nichrome, fechral and other alloys are used to manufacture working elements of electric furnaces and heaters.
The most electrically conductive metal is precious silver, mostly used by jewelers, for minting coins, etc. But its special chemical and physical properties are also widely used in technology and instrument making. For example, in addition to being used in components and assemblies with reduced resistance, silver plating protects contact groups from oxidation. The unique properties of silver and alloys based on it often make its use justified, despite its high cost.
Source: https://FB.ru/article/222201/samyiy-elektroprovodnyiy-metall-v-mire
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Specific conductivity of metals and alloys
The classical theory of electrical conductivity of metals originated at the beginning of the twentieth century. Its founder was the German physicist Karl Rikke. He experimentally established that the passage of a charge through a metal does not involve the transfer of conductor atoms, unlike liquid electrolytes.
However, this discovery did not explain what exactly is the carrier of electrical impulses in the metal structure. The experiments of scientists Stewart and Tolman, conducted last year, allowed us to answer this question.
They were able to establish that the smallest charged particles - electrons - are responsible for the transfer of electricity in metals.
This discovery formed the basis of the classical electronic theory of electrical conductivity of metals. From this moment on, a new era of research into metal conductors began. Thanks to the results obtained, today we have the opportunity to use household appliances, production equipment, machines and many other devices.
The electronic theory of electrical conductivity of metals was developed in the research of Paul Drude. He was able to discover such a property as resistance, which is observed when electric current passes through a conductor.
In the future, this will make it possible to classify different substances according to their conductivity level. From the results obtained, it is easy to understand which metal is suitable for the manufacture of a particular cable.
This is a very important point, since incorrectly selected material can cause a fire as a result of overheating from the passage of excess voltage current. Silver metal has the highest electrical conductivity. But making wiring from silver is very expensive, since it is a rather rare metal, which is used mainly for the production of jewelry and decorative items or bullion coins.
The metal with the highest electrical conductivity among all elements of the base group is copper. Copper is one of the most common conductors used for household and industrial purposes. It withstands constant electrical loads well, is durable and reliable.
The high melting point allows you to work for a long time in a heated state without problems. In terms of abundance, only aluminum can compete with copper, which ranks fourth in electrical conductivity after gold. It is used in networks with low voltage, as it has almost half the melting point of copper and is not able to withstand extreme loads.
The further distribution of places can be found by looking at the table of electrical conductivity of metals. It is worth noting that any alloy has much lower conductivity than the pure substance. This is due to the merging of the structural network and, as a consequence, disruption of the normal functioning of electrons. All given indicators are the electrical conductivity of metals, which is calculated as the ratio between the current density and the magnitude of the electric field in the conductor.
The basic principles of the theory of electrical conductivity of metals contain six points. First: a high level of electrical conductivity is associated with the presence of a large number of free electrons. Second: electric current arises through external influence on the metal, during which electrons move from random motion to ordered one. Third: the strength of the current passing through a metal conductor is calculated according to Ohm's law.
Fourth: different numbers of elementary particles in the crystal lattice lead to unequal resistance of metals. Fifth: electric current in the circuit arises instantly after the start of exposure to electrons. Sixth: as the internal temperature of the metal increases, the level of its resistance also increases. The nature of the electrical conductivity of metals is explained by the second point of the provisions. In a quiet state, all free electrons rotate chaotically around the nucleus.
At this moment, the metal is not able to independently reproduce electrical charges. But as soon as you connect an external source of influence, the electrons instantly line up in a structured sequence and become carriers of electric current.
With increasing temperature, the electrical conductivity of metals decreases. This is due to the fact that the molecular bonds in the crystal lattice weaken, elementary particles begin to rotate in an even more chaotic order, so the formation of electrons in a chain becomes more complicated.
Therefore, it is necessary to take measures to prevent overheating of the conductors, as this negatively affects their performance properties. The mechanism of electrical conductivity of metals cannot be changed due to the current laws of physics.
But it is possible to neutralize negative external and internal influences that interfere with the normal course of the process. The electrical conductivity of alkali metals is at a high level, since their electrons are weakly attached to the nucleus and easily line up in the desired sequence. But this group is characterized by low melting points and enormous chemical activity, which in most cases does not allow their use for the manufacture of wires.
Metals with high electrical conductivity when opened are very dangerous for humans. Touching a bare wire will result in an electrical burn and a powerful discharge to all internal organs. This often results in instant death.
Therefore, special insulating materials are used for the safety of people. Depending on the application, they can be solid, liquid or gaseous.
But all types are designed to do one thing—isolating electrical current within a circuit so that it cannot affect the outside world.
The electrical conductivity of metals is used in almost all areas of modern human life, so ensuring safety is a top priority. When using electrical appliances, a person constantly encounters substances that are conductors, semiconductors and dielectrics that do not conduct current. These materials differ in the degree of electrical conductivity.
In order to work with household appliances, you need to know all their features and characteristics. You can choose the best conductor of electric current from metals.
Current conductors are those substances in which the number of free electrical charges exceeds the number of bound ones. They may begin to move under the influence of an external force.
The state of materials can be gaseous, solid and liquid. Electricity can flow through a metal wire if it is connected between two conductors of different potentials. The current is carried by electrons that are not connected by atoms. They are the ones who are able to characterize the ability of an object to pass electrical charges through itself, or the amount of current conductivity.
The main carriers of electricity in nature are ions, holes and electrons. Therefore, conductivity ability is divided into three types:. The applied voltage makes it possible to evaluate the quality of the conductor. This ability of a substance is also called the current-voltage characteristic. After you have figured out what conducts electric current, you need to find out the characteristics of some substances.
Conductors can be different - metal wire, sea water. But the current in them differs, so substances are divided into two groups: The former include all metals and carbon. The second type includes alkalis, acids, and molten salts—electrolytes.
In them, the current represents the ordered movement of negative and positive ions. Electricity flows in such materials at any voltage level.
Under normal conditions, a good conductor of electric current is a product made of gold, silver, aluminum or copper. The latter two materials produce cables that are low cost.
A high-quality liquid substance that conducts current is mercury, and current flows well through carbon. But this substance is not flexible, so it is not used in practice. Although physicists have recently been able to imagine carbon in the form of graphene, which has made it possible to make cords from its threads.
Graphene products have such a resistance that it is unacceptable for conductors. They can only be used in heaters. In this case, metal wires made of nickel and chromium lose out, since they cannot withstand very high temperatures. Spirals in fluorescent lamps are made of tungsten. This material is capable of heating up, since the substance is refractory. During the flow of electricity, the conductor comes under a certain influence.
The most important thing is the increase in temperature. They also release some chemical reactions that can change the physical properties of a substance. Conductors of the second kind are most exposed to this influence.
A chemical reaction occurs in them, which is called electrolysis. The ions of substances near the electric poles receive the necessary charge and restore the original state that they had before the formation of an alkali, acid or salt.
Using electrolysis, chemists and physicists can produce pure chemicals from natural raw materials.
Aluminum and other types of metals are created in this way. Substances of the first and second kind participate in processes other than conduction of electricity. For example, when acid reacts with lead, a chemical reaction occurs that causes the release of current. All batteries work on this principle. The conductors of the first group may change when in contact with each other. During operation, copper and aluminum must be covered with a special shell, otherwise both metals will simply melt.
Humid air will cause an electrochemical reaction to occur. Some conductors cannot resist electricity in cold air. This phenomenon is called superconductivity, which corresponds to a temperature value close to the chemical state of liquid helium.
But research has led to the fact that there are new conductors with high temperatures.
What substances conduct electric current?
What are their features and what are their distinctive properties? How dangerous can their compounds be to human health? What is the operating principle of fire retardant coatings? The most popular is the hot galvanizing method. Density of metals and alloys Hardness of metals Melting point of metals Specific conductivity of metals. What are the most effective ways to protect metals from corrosion today?
Different substances conduct electric current at different times. Of the metals, the best conductors of electricity are silver, copper, and aluminum. Even in a regular one.
Conductors: Silver, Copper, Aluminum, Iron, Gold, Nickel, Tungsten, Mercury
When an electrical charge is applied to metal at certain points, electrons will move and conduct electricity. But what materials are the highest quality conductors? Of course, these are metals, and we will tell you which ones below. Silver is a better conductor of electricity because it contains more mobile atoms of free electrons.
For a material to be a good conductor, electricity passing through it must move electrons; The more free electrons there are in a metal, the greater its conductivity. However, silver is more expensive than other materials and is not typically used unless required for specialized equipment such as satellites or circuit boards.
Copper is less conductive than silver, but is less expensive and is commonly used as an efficient conductor in household appliances.
Which metal conducts current better?
Source: https://all-audio.pro/c10/instruktsii/chto-provodit-tok-luchshe-serebro-ili-med.php
Electric current in metals
Definition 1
Electric current in metals is the orderly movement of electrons under the influence of an electric field.
Based on experiments, it is clear that a metal conductor does not transfer substances, that is, metal ions do not participate in the movement of electric charge.
Current carriers in metals
The studies provided evidence of the electronic nature of current in metals. Back in 1913, L.I. Mandelstam and N.D. Papalexi produced the first high-quality results. And in 1916, R. Tolman and B. Stewart modernized the existing technique and performed quantitative measurements that proved that the movement of electrons occurs under the influence of current in metal conductors.
Figure 1.12.1 shows Tolman and Stewart's diagram. The coil, consisting of a large number of turns of thin wire, was driven by rotation around its axis. Its ends were attached to a ballistic galvanometer G. The coil was suddenly braked, which was a consequence of the occurrence of a short-term current caused by the inertia of the charge carrier. The total charge was measured by moving the needles of the galvanometer.
Figure 1.12.1. Scheme of Tolman and Stewart's experiment.
During the braking of the rotating coil, the force F = -mdυdt, called braking, acted on each charge carrier e. F played the role of an external force, in other words, of non-electric origin. It is this force, characterized by a unit of charge, that is the field strength of external forces Est:
Est=-medυdt.
That is, when the coil is braking, an electromotive force δ appears, equal to δ=Estl=medυdtl, where l is the length of the coil wire. A certain period of time during the braking process of the coil is determined by the flow of charge q through the circuit:
q=∫Idt=1R∫δdt=melυ0R.
This formula explains that l is the instantaneous value of the current in the coil, R is the total resistance of the circuit, υ0 is the initial linear speed of the wire. It can be seen that the specific charge em in metals is determined based on the formula:
em=lυ0Rq.
The quantities on the right side can be measured. Based on the results of the experiments of Tolman and Stewart, it was established that free charge carriers have a negative sign, and the ratio of the carrier in its mass is close to the value of the specific charge of the electron obtained in other experiments. It was revealed that electrons are carriers of free charges.
Modern data show that the electron charge modulus, that is, the elementary charge, is equal to e=1.60218·10-19 C, and the designation of its specific charge is em=1.75882·1011 C/kg.
If there is an excellent concentration of free electrons, it makes sense to talk about good electrical conductivity of metals. This was discovered even before the experiments of Tolman and Stewart. In 1900, P. Drude, based on the hypothesis of the existence of free electrons in metals, created the electronic theory of conductivity of metals. It was developed and expanded by H.
Lorentz, after which it received the name classical electronic theory. Based on it, they realized that electrons behave like an electron gas, similar to an ideal gas in its state. Figure 1.12.2 shows how it can fill the space between the ions that have already formed the crystal lattice of the metal.
Figure 1.12.2. A gas of free electrons in a metal crystal lattice. The trajectory of one of the electrons is shown.
Potential barrier. Movement of electrons in a crystal lattice
Definition 2
After the interaction of electrons with ions, the first leave the metal, overcoming only the potential barrier.
The height of such a barrier is called the work function .
The presence of room temperature prevents electrons from passing through this barrier. The potential energy of an electron's release after interaction with a crystal lattice is much less than when an electron is removed from a conductor.
Definition 3
The location of e in the conductor is characterized by the presence of a potential well, the depth of which is called potential barrier .
Ions forming the lattice and electrons take part in thermal movement. Due to thermal vibrations of ions near equilibrium positions and the chaotic movement of free electrons, when the former collide with the latter, the thermodynamic equilibrium between the electrons and the lattice increases.
Theorem 1
According to the Drude-Lorentz theory, we have that electrons have the same average energy of thermal motion as the molecules of a monatomic ideal gas. This makes it possible to estimate the average speed υт¯ of thermal motion of electrons using molecular kinetic theory.
Room temperature gives a value of 105 m/s.
If you apply an external electric field to a metal conductor, then thermally ordered movement of electrons (electric current), that is, drift, will occur. Determination of its average speed υд¯ is carried out according to the available time interval ∆t through the cross section S of the conductor of electrons that are in the volume Sυд∆t.
The number of such e is equal to nSυд∆t, where n takes the value of the average concentration of free electrons, equal to the number of atoms per unit volume of a metal conductor. For the available amount of time ∆t, a charge ∆q=enSυд∆t passes through the cross section of the conductor.
Then I=∆q∆t=enSυд or υд=IenS.
The concentration of n atoms in metals is in the range of 1028-1029m-3.
The formula makes it possible to estimate the average speed υд¯ of the ordered movement of electrons with a value in the range of 0.6-6 mm/s for a conductor with a cross-section of 1 mm2 and a passing current of 10 A.
Definition 4
The average speed υд¯ of the ordered movement of electrons in metal conductors is many orders of magnitude less than the speed υт of their thermal movement υд≪υт.
Figure 1.12.3 demonstrates the nature of the movement of free e located in the crystal lattice.
Figure 1.12.3. Movement of a free electron in a crystal lattice: a – chaotic movement of an electron in a metal crystal lattice; b – chaotic motion with drift caused by the electric field. The scale of the drift υд¯∆t is greatly exaggerated.
The presence of a low drift speed does not correspond to the experience when the current of the entire DC circuit is established instantly. The closure is effected by an electric field at a speed of c=3·108 m/s. After time lc (l is the length of the chain), a stationary distribution of the electric field is established along the chain. There is an ordered movement of electrons in it.
The classical electronic theory of metals assumes that their motion is subject to Newton's laws of mechanics. This theory is characterized by the fact that the interaction of electrons with each other is neglected, and the interaction with positive ions is regarded as collisions, during each of which e imparts accumulated energy to the lattice. Therefore, it is generally accepted that after a collision the motion of an electron is characterized by zero drift velocity.
Absolutely all of the above proposed assumptions are approximate. This makes it possible to explain the laws of electric current in metal conductors, based on the electronic classical theory.
Ohm's law
Definition 5
In the interval between collisions, a force equal in magnitude eE acts on the electron, as a result of which it receives acceleration emE.
The end of the free path is characterized by the drift velocity of the electron, which is determined by the formula
υд=υдmax=eEmτ.
The free travel time is denoted by τ. It helps simplify the calculations for finding the value of all electrons. The average drift speed υd is equal to half the maximum value:
υд=12υдmax=12eEmτ.
If there is a conductor with length l, cross-section S with electron concentration n, then the record of the current in the conductor has the form:
I=enSυd=12e2τnSmE=e2τnS2mlU.
U=El is the voltage at the ends of the conductor. The formula expresses Ohm's law for a metal conductor. Then the electrical resistance must be found:
R=2me2nτlS.
Resistivity ρ and conductivity ν are expressed as:
ρ=2me2nτ; ν=1ρ=e2nτ2m.
Joule-Lenz law
The end of the path of electrons under the influence of a field is characterized by kinetic energy
12m(υd)max2=12e2τ2mE2.
Definition 6
Based on assumptions, energy during collisions is transferred to the lattice, and subsequently turns into heat.
Time ∆t each electron undergoes ∆tτ collisions. A conductor with cross section S and length l has nSl electrons. Then the heat released in the conductor for ∆t is equal to
∆Q=nSl∆tτe2τ22mE2=ne2τ2mSlU2∆t=U2R∆t.
This relationship expresses the Joule-Lenz law .
Thanks to the classical theory, there is an interpretation of the existence of electrical resistance of metals, that is, Ohm's and Joule-Lenz's laws. Classical electron theory is not able to answer all questions.
It is not able to explain the difference in the value of the molar heat capacity of metals and dielectric crystals, equal to 3R, where R is written as the universal gas constant. The heat capacity of a metal does not depend on the number of free electrons.
The classical electronic theory does not explain the temperature dependence of the resistivity of metals. According to theory, ρ~T, and based on experiments – ρ~T. An example of the discrepancy between theory and practice is superconductivity.
Metal conductor resistance
Based on the classical theory, the resistivity of metals should gradually decrease with decreasing temperature, and remain finite at any T. This dependence is typical for experiments at high temperatures. If T is low enough, then the resistivity of metals loses its dependence on temperature and reaches a limiting value.
Of particular interest was the phenomenon of superconductivity. In 1911 it was discovered by H. Kammerling-Onnes.
Theorem 2
If there is a certain temperature Tcr, different for different substances, then the resistivity decreases to zero using a jump, as shown in Figure 1.12.4.
Example 1
The critical temperature for mercury is considered to be 4.1 K, for aluminum - 1.2 K, for tin - 3.7 K. The presence of superconductivity can be not only in elements, but also in chemical compounds and alloys.
Niobium and tin Ni3Sn have a critical temperature point of 18 K. There are substances that at low temperatures transform into a superconducting state, whereas under normal conditions they are not.
Silver and copper are conductors, but do not become superconductors when the temperature drops.
Figure 1.12.4. Dependence of resistivity ρ on absolute temperature T at low temperatures: a – normal metal; b – superconductor.
The superconducting state indicates the exceptional properties of a substance. One of the most important is the ability to maintain an electric current excited in a superconducting circuit for a long time without attenuation.
Classical electron theory cannot explain superconductivity. This became possible 60 years after its discovery, based on quantum mechanical concepts.
Interest in this phenomenon increased with the emergence of new materials capable of high critical temperatures. In 1986, a complex compound with a temperature Tcr = 35 K was discovered. The following year, they managed to create ceramics with a critical T of 98 K, which exceeded the T of liquid nitrogen (77 K).
Definition 7
The phenomenon of the transition of substances into a superconducting state at temperatures exceeding the boiling point of liquid nitrogen is called high-temperature superconductivity .
Later, in 1988, a Tl-Ca-Ba-Cu-O compound was created with a critical T reaching 125 K. At the moment, scientists are interested in finding new substances with the highest Tcr values. They hope to obtain a superconducting substance at room temperature. If this is done, there will be a revolution in science and technology. To date, all the properties and mechanisms of the composition of superconducting ceramic materials have not been fully studied.
Source: https://Zaochnik.com/spravochnik/fizika/postojannyj-elektricheskij-tok/elektricheskij-tok-v-metallah/
Application of electric current in metals
Almost all metals can be considered as conductors of electric current. This is due to their structure, which is a crystalline spatial lattice. The nodes of this lattice coincide with the centers of positive ions, around which chaotic movement of free electrons is observed. This explains the phenomenon of conductivity, due to which the use of electric current in metals has become most widespread.
Physical properties of metals
The properties of metals depend entirely on their internal structure. The solid state of metals is a spatial crystal lattice, where the crystals are arranged in an orderly manner. As already noted, the movement of free electrons is observed between the nodes of the crystal lattice.
The absolute value of their negative charges coincides with the positive charge of all ions located at the sites of the crystal lattice. When electric current is passed through a conductor, the ions remain in place. There is a movement of free electrons, the same in any substance.
Electric current in metals: application
The fact that metals contain electrons that conduct current has been proven a long time ago. First of all, these useful properties are used when transmitting electricity from sources to consumers. The operation of generators and electric motors is also based on the physical properties of metals. They are also used in heating devices of all types intended for industrial production and home use.
Thus, electric current in metals is the ordered movement of free electrons, which are affected by an electric field. In its absence, the movement of electrons becomes chaotic, similar to the movement of molecules of liquids or gases. However, if there is an electric field in the conductor, electrons shift to the positive pole of the current source, that is, their movement becomes ordered.
The electrons themselves move at a low speed in a conductor, in contrast to the electric field, which moves in a conductor at a speed approaching the speed of light. It is this value that serves as an indicator of the speed of propagation of electric current in a conductor.
Electric current in metal: electronic conductivity
Source: https://electric-220.ru/news/primenenie_ehlektricheskogo_toka_v_metallakh/2014-10-26-727
What is electricity and how does it arise ⋆ diodov.net
Electronics is a wonderful applied and theoretical science that is gaining momentum every day, spreading and being introduced into all industries. Its study should begin with the most general concepts and physical processes. Knowledge of which will further simplify the understanding of the operating principles of various electronic devices and devices. And the first concept that we need to understand is what is electricity?
Discovery of electricity
The properties of electricity were first discovered more than 2.5 thousand years ago by the ancient philosopher Thales of Miletus, when he rubbed amber with wool.
An attentive philosopher noticed that small objects are attracted to an already rubbed gem. Although, according to the logic formed at the level of knowledge of that time, all objects should have been attracted to the earth, i.e. fall to the ground under the influence of gravity.
However, amber rubbed with wool acquired some mysterious property, later called a charge, which created a force greater in magnitude than the force of gravity. And this force was called “electricity”.
Since the word “electron” is translated from Greek as “amber,” electricity can be literally translated as amber.
In those ancient times, it was believed that only amber had some mysterious property that, after rubbing with wool, could attract light objects, overcoming the force of gravity. However, now a similar experience is quite easy to repeat if, instead of this stone, you take a plastic stick and rub it on clothes containing wool. Then, when you bring the rubbed stick to small pieces of paper, under the influence of electrical forces, the pieces of paper will be attracted to the stick.
From the above, let's highlight two important points:
- Only after rubbing it against wool does the plastic stick acquire certain properties.
- The acquired properties generate a certain force, under the influence of which pieces of paper are attracted to the stick.
Now we clearly know what questions we need to answer in order to understand what electricity is.
Let's look at the physics of the ongoing process. And first of all, in order to analyze what happens to a substance (in this case, plastic and wool), we need knowledge about the structure of any substance. Let us say in advance that in the further story we will accept generalizations and simplifications, but they will not distort the essence of this topic.
Atomic structure
So, let's begin. Any substance, be it wood, stone, glass or water, consists of smaller elements called molecules. For example, a drop of water consists of many individual molecules with the familiar chemical formula H2O. Further, the molecule of the substance can be divided into even smaller particles - atoms .
At one time it was believed that the atom was the smallest particle existing in nature and it was no longer possible to divide it into smaller elements. Therefore, the word “atom” is translated from the ancient Greek “indivisible”.
Now only more than a hundred different atoms are known, but they can form millions of different molecules and, accordingly, as many different substances. For example, the water molecule H2O is formed by two hydrogen atoms H and one oxygen atom O.
Over time, after doing many painstaking experiments, scientists came to the conclusion about the existence of much smaller particles.
Planetary model of the atom
The central and heaviest element of an atom is considered to be the nucleus. Electrons move around it at a certain distance in different orbits. The nucleus is not a solid element; it is made up of protons and neutrons.
Electrons have a negative charge, and protons have a positive charge. The neutron does not exhibit the properties of either charge, i.e. it is neutral, hence its name.
To simplify some processes, a planetary model of the atom is used. By analogy with the Sun, around which the planets move in orbits, in an atom electrons move around the nucleus. But an electron is not some kind of dense particle, but a clot of energy spread out in space, like flattened ball lightning.
The mass of a proton is approximately 2000 times the mass of an electron. But the total positive electric charge of all protons is equal to the total negative charge of all electrons. Therefore, under normal (default) conditions, the atom is electrically neutral and no forces are felt outside of it. Positive and negative charges seem to neutralize each other.
In the periodic system of chemical elements, known to us as the periodic table, all atoms are arranged in a strict sequence: from the lightest to the heaviest - according to the relative atomic mass, the main share of which is made up of protons. Neutrons also have mass, but we will not talk about them, since they do not have a pronounced electric charge.
The lightest chemical element is hydrogen, which is why it is placed first on the periodic table. A hydrogen atom has one proton and one electron. Other chemical elements contain several protons in the nucleus. And electrons move around the nucleus in several orbits.
The closer the electron is to the nucleus, the stronger, with greater force it is attracted to the proton. Electrons located in the most distant orbits have the weakest electrical connection with protons.
And if an atom is given some energy from the outside, for example, heated, then under the influence of excess energy the electron can leave its orbit, and, accordingly, its atom.
However, it can not only leave the original atom, but also take a place in the orbit of another atom. It is those electrons that are located in the orbits farthest from the nucleus that have practical application in electronics, since in the presence of additional energy they easily leave their orbits and become free. And a free electron, when moving, can already perform some useful work.
Positive and negative ions
As we noted earlier, by default an atom is electrically neutral: positive and negative charges are equal and cancel each other out. But as soon as at least one electron leaves its place in the atom, the total positive electric charge of the protons is dominated by the negative charge of all remaining electrons, therefore such an atom as a whole has the properties of a positive charge and is called a positive ion .
If an atom has received an additional electron, then it will have a predominant negative charge. In this case, the atom is called a negative ion .
It should be noted that not only the atom will have a positive or negative charge, but also the molecule, and accordingly the substance that contains this atom.
Electrification
The process of gaining an additional electron or, conversely, losing an electron is called electrification . If any body has an excess or shortage of electrons, i.e. a clearly expressed charge of any sign, then they say that the body is electrified.
It has been experimentally established that charges of the same sign repel, and charges of different signs attract. A similar experiment can be repeated in the following very well-known way: hang two metal balls, which initially have a neutral charge, on a thread. Next, give one ball a positive charge and the second a negative one. As a result, the balls will be attracted to each other. If two balls are charged with the same sign, they will repel.
Now it's time to return to our experience with rubbing wool on a plastic stick. When the plastic is rubbed due to frictional forces, the electrons located in the atoms of the wool are given some energy, under the influence of which they leave their atoms and take place in the orbits of the plastic atoms. As a result, the plastic stick acquires a negative charge due to the excess electrons coming from the wool.
When rubbing a glass rod with silk, the opposite happens. Electrons from the surface layer of glass leave the rod. In this case, the glass rod acquires a positive charge due to the preponderance of the total charge of protons.
Thus, the change in the number of electrons in the upper layers of the materials in question during their friction is called electrification by friction .
It should be noted here that due to friction, only a very tiny part of the atoms gives up their electrons. Even if we say that one billionth of the atoms remain without electrons in the outer orbit, this will still be too much of an exaggeration, so the masses of electrified bodies remain practically unchanged.
It should also be noted that as a result of electrification, electrons do not appear from anywhere and do not disappear anywhere, but only move from the atoms of one body to the atoms of another body.
In our experience we used glass, plastic, wool, silk. Electrons move very poorly through these materials, so they are classified as good dielectrics - materials that, unlike conductors, have very poor conductivity.
Source: https://diodov.net/chto-takoe-elektrichestvo-i-kak-ono-voznikaet/
The best conductors of electric current: characteristics of substances that transmit electricity
When using electrical appliances, a person constantly encounters substances that are conductors, semiconductors and dielectrics that do not conduct current. These materials differ in the degree of electrical conductivity. In order to work with household appliances, you need to know all their features and characteristics. You can choose the best conductor of electric current from metals.
- Features of the concept
- First and second kind
- Processes in electrical conductors
Current conductors are those substances in which the number of free electrical charges exceeds the number of bound ones. They may begin to move under the influence of an external force. The state of materials can be gaseous, solid and liquid. Electricity can flow through a metal wire if it is connected between two conductors of different potentials.
The current is carried by electrons that are not connected by atoms. They are the ones who are able to characterize the ability of an object to pass electrical charges through itself, or the amount of current conductivity. Its value is inversely proportional to the resistance, it is measured in siemens: cm = 1/Ohm.
The main carriers of electricity in nature are ions, holes and electrons. Therefore, conductivity ability is divided into three types:
- ionic;
- electronic;
- hole
The applied voltage makes it possible to evaluate the quality of the conductor. This ability of a substance is also called the current-voltage characteristic.
First and second kind
After you have figured out what conducts electric current, you need to find out the characteristics of some substances. Conductors can be different - metal wire, sea water. But the current in them differs, so substances are divided into two groups:
- the first kind, in which electricity flows through electrons;
- the second type is based on ions.
The former include all metals and carbon. The second type includes alkalis, acids, and molten salts—electrolytes. In them, the current represents the ordered movement of negative and positive ions. Electricity flows in such materials at any voltage level. Under normal conditions, a good conductor of electric current is a product made of gold, silver, aluminum or copper.
The latter two materials produce cables that are low cost. A high-quality liquid substance that conducts current is mercury, and current flows well through carbon. But this substance is not flexible, so it is not used in practice. Although physicists have recently been able to imagine carbon in the form of graphene, which has made it possible to make cords from its threads.
Graphene products have such a resistance that it is unacceptable for conductors. They can only be used in heaters. In this case, metal wires made of nickel and chromium lose out, since they cannot withstand very high temperatures. Spirals in fluorescent lamps are made of tungsten. This material is capable of heating up, since the substance is refractory.
Processes in electrical conductors
During the flow of electricity, the conductor comes under a certain influence. The most important thing is the increase in temperature. They also release some chemical reactions that can change the physical properties of a substance. Conductors of the second kind are most exposed to this influence. A chemical reaction occurs in them, which is called electrolysis.
The ions of substances near the electric poles receive the necessary charge and restore the original state that they had before the formation of an alkali, acid or salt. Using electrolysis, chemists and physicists can produce pure chemicals from natural raw materials. Aluminum and other types of metals are created in this way.
Substances of the first and second kind participate in processes other than conduction of electricity. For example, when acid reacts with lead, a chemical reaction occurs that causes the release of current. All batteries work on this principle.
The conductors of the first group may change when in contact with each other. During operation, copper and aluminum must be covered with a special shell, otherwise both metals will simply melt. Humid air will cause an electrochemical reaction to occur.
Therefore, the conductors are coated with a layer of varnish or other protective material.
Some conductors cannot resist electricity in cold air. This phenomenon is called superconductivity, which corresponds to a temperature value close to the chemical state of liquid helium. But research has led to the fact that there are new conductors with high temperatures.
Such substances were discovered in the 20th century. Ceramics made of oxygen, barium, copper and lanthanum do not conduct current under normal conditions, but when heated they become superconductors . In practice, it is advantageous to use substances that can transmit electricity at 58 degrees Kelvin and above, a temperature above the boiling point of nitrogen.
Liquids and gases that conduct current are used less often than solids. But they are also necessary for the manufacture of modern electrical appliances.
Source: https://220v.guru/elementy-elektriki/provodka/luchshie-provodniki-elektricheskogo-toka.html
III. Basics of electrodynamics
As you know, chemically pure (distilled) water is a poor conductor. However, when various substances (acids, alkalis, salts, etc.) are dissolved in water, the solution becomes a conductor due to the breakdown of the molecules of the substance into ions. This phenomenon is called electrolytic dissociation , and the solution itself is an electrolyte capable of conducting current.
Unlike metals and gases, the passage of current through an electrolyte is accompanied by chemical reactions at the electrodes, which leads to the release of chemical elements that make up the electrolyte on them.
Faraday's first law: the mass of a substance released on any of the electrodes is directly proportional to the charge passing through the electrolyte
The electrochemical equivalent of a substance is a tabular value.
Faraday's second law:
The flow of current in liquids is accompanied by the release of heat. In this case, the Joule-Lenz law is fulfilled.
Electric current in metals
When current passes, the metals heat up. As a result, the ions of the crystal lattice begin to vibrate with greater amplitude near the equilibrium positions. As a result, the flow of electrons more often collides with the crystal lattice, and consequently the resistance to their movement increases. As the temperature increases, the resistance of the conductor increases.
Each substance is characterized by its own temperature coefficient of resistance - a tabular value. There are special alloys whose resistance practically does not change when heated, for example manganin and constantan.
The phenomenon of superconductivity. At temperatures close to absolute zero (-2730C), the resistivity of the conductor abruptly drops to zero. Superconductivity is a microscopic quantum effect.
Application of electric current in metals
An incandescent light bulb produces light by electric current flowing through a filament. The filament material has a high melting point (for example, tungsten), as it heats up to a temperature of 2500 - 3250K. The filament is placed in a glass flask with an inert gas.
Electric current in gases
Gases in their natural state do not conduct electricity (they are dielectrics), since they consist of electrically neutral atoms and molecules. An ionized gas containing electrons, positive and negative ions can become a conductor.
Ionization can occur under the influence of high temperatures, various radiations (ultraviolet, x-rays, radioactive), cosmic rays, and collisions of particles with each other.
The ionized state of the gas is called plasma . On the scale of the Universe, plasma is the most common state of matter. The Sun, stars, and the upper layers of the atmosphere are made of it.
The passage of electric current through a gas is called a gas discharge .
A glow discharge flows in the “advertising” neon tube . The glowing gas is “living plasma.”
An arc discharge occurs between the electrodes of the welding machine .
An arc discharge occurs in mercury lamps, which are very bright light sources.
a spark discharge in lightning. Here the electric field strength reaches the breakdown value. The current strength is about 10 MA!
A corona discharge by gas glowing, forming a “corona” surrounding the electrode.
Corona discharge is the main source of energy loss in high-voltage power lines.
Electric current in a vacuum
Is it possible for electric current to propagate in a vacuum (from the Latin vacuum - emptiness)? Since there are no free charge carriers in a vacuum, it is an ideal dielectric. The appearance of ions would lead to the disappearance of the vacuum and the production of ionized gas. But the appearance of free electrons will ensure the flow of current through the vacuum. How to get free electrons in a vacuum? Using the phenomenon of thermionic emission - the emission of electrons by a substance when heated.
Vacuum diode, triode, cathode ray tube (in old TVs) are devices whose operation is based on the phenomenon of thermionic emission. The basic principle of operation: the presence of a refractory material through which current flows - cathode , a cold electrode that collects thermionic electrons - anode .
Source: http://fizmat.by/kursy/jelektricheskij_tok/sreda_toka
Electrical conductivity in metals 2020
Electrical conductivity in metals results from the movement of electrically charged particles.
Atoms of metallic elements are characterized by the presence of valence electrons—electrons in the outer shell of the atom that can move freely. It is these “free electrons” that allow metals to conduct electric current.
Because valence electrons are free to move, they can pass through the lattice that forms the physical structure of the metal.
Under an electric field, free electrons move through the metal much like billiard balls clattering together, passing electrical charge as they move.
Energy transfer is greater when resistance is low. On a pool table, this occurs when the ball hits another single ball, transferring most of its energy to the next ball. If one ball hits several other balls, each of them will carry only a portion of the energy.
In addition, the most efficient conductors of electricity are metals that have one valence electron that moves freely and causes a strong repulsion reaction in other electrons. This occurs in the most conductive metals such as silver, gold and copper, each of which has a single valence electron that moves with little resistance and produces a strong repulsive reaction.
Semiconducting metals (or metalloids) have a higher number of valence electrons (usually four or more), so although they can conduct electricity, they are inefficient at the task.
However, when heated or doped with other elements, semiconductors such as silicon and germanium can become extremely efficient conductors of electricity.
Conduction in metals must follow Ohm's law, which states that current is directly proportional to the electric field applied to the metal. The key variable in applying Ohm's Law is the resistivity of the metal.
Resistance is the opposite of electrical conductivity, measuring how much a metal opposes the flow of electrical current. This is usually measured across opposing surfaces of a one-meter cube of material and is described as an ohmmeter (Ω⋅m). Resistance is often represented by the Greek letter rho (ρ).
Electrical conductivity, on the other hand, is usually measured in siemens per meter (S⋅m -1) and is represented by the Greek letter sigma (σ). One siemens is equal to the inverse of one ohm.
Conductivity and resistance in metals
| Silver | 1. 59×10 -8 | 6. 30×10 7 |
| Copper | 1. 68×10 -8 | 5. 98×10 7 |
| Annealing of copper | 1. 72×10 -8 | 5. 80×10 7 |
| Gold | 2.44×10 -8 | 4. 52×10 7 |
| Aluminum | 2. 82×10 -8 | 3. 5×10 7 |
| Calcium | 3. 36×10 -8 | 2. 82×10 7 |
| Beryllium | 4. 00×10 -8 | 2. 500×10 7 |
| Rhodium | 4. 49×10 -8 | 2. 23×10 7 |
| Magnesium | 4. 66×10 -8 | 2. 15×10 7 |
| Molybdenum | 5. 225×10 -8 | 1. 914×10 7 |
| Iridium | 5. 289×10 -8 | 1. 891×10 7 |
| Tungsten | 5. 49×10 -8 | 1. 82×10 7 |
| Zinc | 5. 945×10 -8 | 1. 682×10 7 |
| Cobalt | 6. 25×10 -8 | 1. 60×10 7 |
| Cadmium | 6. 84×10 -8 | 1. 46 7 |
| Nickel (electrolytic) | 6. 84×10 -8 | 1. 46×10 7 |
| ruthenium | 7. 595×10 -8 | 1. 31×10 7 |
| Lithium | 8. 54×10 -8 | 1. 17×10 7 |
| Iron | 9. 58×10 -8 | 1. 04×10 7 |
| Platinum | 1. 06×10 -7 | 9. 44×10 6 |
| Palladium | 1. 08×10 -7 | 9. 28×10 6 |
| Tin | 1. 15×10 -7 | 8. 7×10 6 |
| Selenium | 1. 197×10 -7 | 8. 35×10 6 |
| Tantalum | 1. 24×10 -7 | 8. 06×10 6 |
| Niobium | 1. 31×10 -7 | 7. 66×10 6 |
| Steel (Cast) | 1. 61×10 -7 | 6. 21×10 6 |
| Chromium | 1. 96×10 -7 | 5. 10×10 6 |
| Lead | 2. 05×10 -7 | 4. 87×10 6 |
| Vanadium | 2. 61×10 -7 | 3. 83×10 6 |
| Uranus | 2. 87×10 -7 | 3. 48×10 6 |
| Antimony* | 3. 92×10 -7 | 2. 55×10 6 |
| Zirconium | 4. 105×10 -7 | 2. 44×10 6 |
| Titanium | 5. 56×10 -7 | 1. 798×10 6 |
| Mercury | 9. 58×10 -7 | 1. 044×10 6 |
| Germanium* | 4. 6×10 1 | 2. 17 |
| silicon* | 6. 40×10 2 | 1. 56×10 -3 |
*Note: The resistivity of semiconductors (metalloids) is highly dependent on the presence of impurities in the material.
Chart source data
Eddy Current Technology Inc. URL: // eddy currents. com/conductivity-of-metals-sorting by resistivity/Wikipedia: Electrical conductivity
URL: // ru. Wikipedia. org/wiki/Electrical_conductivity
Source: https://ru.routestofinance.com/electrical-conductivity-in-metals
Electric current in metals - materials for preparing for the Unified State Exam in Physics
The author of the article is a professional tutor, author of textbooks for preparing for the Unified State Exam Igor Vyacheslavovich Yakovlev
Topics of the Unified State Examination codifier: carriers of free electric charges in metals
In this worksheet, we begin a detailed study of how electric current flows in various conducting media - solids, liquids and gases.
Let us recall that a necessary condition for the occurrence of a current is the presence in the medium of a sufficiently large number of free charges that can begin to move in an orderly manner under the influence of an electric field. Such media are precisely called conductors of electric current.
Metal conductors are the most widely used. Therefore, we begin with questions of the propagation of electric current in metals.
We have talked many times about free electrons, which are carriers of free charges in metals. You are well aware that electric current in a metal conductor is formed as a result of the directed movement of free electrons.
Free electrons
Metals in the solid state have a crystalline structure: the arrangement of atoms in space is characterized by periodic repetition and forms a geometrically regular pattern, called a crystal lattice.
Metal atoms have a small number of valence electrons located in the outer electron shell. These valence electrons are weakly bound to the nucleus and the atom can easily lose them.
When metal atoms occupy places in the crystal lattice, valence electrons leave their shells - they become free and go “walking” throughout the crystal (namely, free electrons move along the outer orbitals of neighboring atoms.
These orbitals overlap each other due to the close arrangement of atoms in the crystal lattice, so that free electrons are the “common property” of the entire crystal).
Positive ions remain at the nodes of the metal crystal lattice, the space between which is filled with a “gas” of free electrons (Fig. 1).
Rice. 1. Free electrons
Free electrons indeed behave like gas particles (another adequate image is the electron sea that “washes” the crystal lattice) - performing thermal motion, they chaotically scurry back and forth between the ions of the crystal lattice. The total charge of free electrons is equal in magnitude and opposite in sign to the total charge of positive ions, therefore the metal conductor as a whole turns out to be electrically neutral.
The gas of free electrons is the “glue” that holds the entire crystalline structure of a conductor together.
After all, positive ions repel each other, so that the crystal lattice, bursting from the inside with powerful Coulomb forces, could fly apart in different directions.
However, at the same time, the metal ions are attracted to the electron gas enveloping them and, as if nothing had happened, remain in their places, performing only thermal vibrations at the nodes of the crystal lattice near the equilibrium positions.
What happens if a metal conductor is connected to a closed circuit containing a current source? Free electrons continue to perform chaotic thermal motion, but now - under the influence of the emerging external electric field - they will also begin to move in an orderly manner.
This directional flow of electron gas, superimposed on the thermal movement of electrons, is the electric current in the metal (therefore, free electrons are also called conduction electrons).
The speed of ordered movement of electrons in a metal conductor, as we already know, is approximately 0.1 mm/s.
Rikke's Experience
Why did we decide that current in metals is created by the movement of free electrons? Positive ions of the crystal lattice also experience the action of an external electric field. Maybe they also move inside a metal conductor and participate in the creation of current?
The ordered movement of ions would mean a gradual transfer of matter along the direction of the electric current. Therefore, you just need to pass current through the conductor for a very long time and see what happens in the end. This kind of experiment was carried out by E. Rikke in 1901.
Three cylinders pressed against each other were included in the electrical circuit: two copper cylinders at the edges and one aluminum cylinder between them (Fig. 2). Electric current was passed through this circuit for a year.
Rice. 2. Rikke's experience
Over the course of a year, a charge of more than three million coulombs passed through the cylinders. Let us assume that each metal atom loses one valence electron, so that the charge of the ion is equal to the elementary charge Cl. If the current is created by the movement of positive ions, then it is easy to calculate (do it yourself!) that this amount of charge passed through the circuit corresponds to the transfer of about 2 kg of copper along the chain.
However, after separating the cylinders, only a slight penetration of the metals into each other was discovered, due to the natural diffusion of their atoms (and nothing more). Electric current in metals is not accompanied by the transfer of matter, so positive ions of the metal do not take part in creating the current.
Stewart–Tolman experiment
Direct experimental proof that electric current in metals is created by the movement of free electrons was given in the experiment of T. Stewart and R. Tolman (1916).
The Stewart–Tolman experiment was preceded by qualitative observations made four years earlier by Russian physicists L.I. Mandelstam and N.D. Papaleksi. They drew attention to the so-called electroinertial effect: if you sharply brake a moving conductor, a short-term current pulse appears in it. The effect is explained by the fact that for a short time after the conductor is decelerated, its free charges continue to move by inertia.
However, Mandelstam and Papaleksi did not obtain any quantitative results, and their observations were not published. The honor of calling the experiment by its name belongs to Stewart and Tolman, who not only observed the indicated electroinertial effect, but also made the necessary measurements and calculations.
The Stewart and Tolman setup is shown in Fig. 3.
Rice. 3. Stewart–Tolman experiment
The coil was driven into rapid rotation around its axis by a large number of turns of metal wire. The ends of the winding were connected using sliding contacts to a special device - a ballistic galvanometer, which allows you to measure the charge passing through it.
After a sharp braking of the coil, a current pulse appeared in the circuit. The direction of the current indicated that it was caused by the movement of negative charges. By measuring the total charge passing through the circuit with a ballistic galvanometer, Stewart and Tolman calculated the ratio of the charge of one particle to its mass. It turned out to be equal to the ratio for the electron, which was already well known at that time.
Thus, it was finally found out that the carriers of free charges in metals are free electrons. As you can see, this fact, which has long been well known to you, was established relatively late - given that metal conductors by that time had already been actively used for more than a century in a wide variety of experiments in electromagnetism (compare, for example, with the date of discovery of Ohm's law - 1826. Case, however, is that the electron itself was discovered only in 1897).
Dependence of resistance on temperature
Experience shows that when a metal conductor is heated, its resistance increases. How to explain this?
The reason is simple: with increasing temperature, thermal vibrations of the ions of the crystal lattice become more intense, so that the number of collisions of free electrons with ions increases.
The more active the thermal motion of the lattice, the more difficult it is for electrons to get through the gaps between the ions (Imagine a rotating passage door. In which case is it more difficult to slip through it: when it rotates slowly or quickly? :-)).
The speed of the ordered movement of electrons decreases, therefore the current strength decreases (at a constant voltage). This means an increase in resistance.
As experience again shows, the dependence of the resistance of a metal conductor on temperature is linear with good accuracy:
(1)
Here is the conductor resistance at . The dependence graph (1) is a straight line (Fig. 4).
Rice. 4.
The multiplier is called the temperature coefficient of resistance. Its values for various metals and alloys can be found in tables.
The length of the conductor and its cross-sectional area do not change significantly with temperature changes. Let us also express it in terms of resistivity:
and substitute these formulas into (1). We obtain a similar dependence of resistivity on temperature:
The coefficient is very small (for copper, for example), so that the temperature dependence of the metal’s resistance can often be neglected. However, in some cases you have to take it into account. For example, the tungsten filament of an electric light bulb heats up to such an extent that its current-voltage characteristic turns out to be significantly nonlinear.
Rice. 5. Volt-ampere characteristic of a light bulb
So, in Fig. Figure 5 shows the current-voltage characteristic of a car light bulb. If a light bulb were an ideal resistor, its current-voltage characteristic would be a straight line in accordance with Ohm's law. This straight line is shown as a blue dotted line.
However, as the voltage applied to the light bulb increases, the graph deviates from this straight line more and more. Why? The fact is that with increasing voltage, the current through the light bulb increases and heats the coil more; The resistance of the spiral therefore also increases. Consequently, although the current strength will continue to increase, it will have a smaller and smaller value compared to that prescribed by the “dotted” linear dependence of current on voltage.
Source: https://ege-study.ru/ru/ege/materialy/fizika/elektricheskij-tok-v-metallax/
Electrical conductivity of metals
The classical theory of electrical conductivity of metals originated at the beginning of the twentieth century. Its founder was the German physicist Karl Rikke. He experimentally established that the passage of a charge through a metal does not involve the transfer of conductor atoms, unlike liquid electrolytes. However, this discovery did not explain what exactly is the carrier of electrical impulses in the metal structure.
The experiments of scientists Stewart and Tolman, conducted in 1916, allowed us to answer this question. They were able to establish that the smallest charged particles - electrons - are responsible for the transfer of electricity in metals.
This discovery formed the basis of the classical electronic theory of electrical conductivity of metals. From this moment on, a new era of research into metal conductors began.
Thanks to the results obtained, today we have the opportunity to use household appliances, production equipment, machines and many other devices.
How does the electrical conductivity of different metals differ?
The electronic theory of electrical conductivity of metals was developed in the research of Paul Drude. He was able to discover such a property as resistance, which is observed when electric current passes through a conductor.
In the future, this will make it possible to classify different substances according to their conductivity level. From the results obtained, it is easy to understand which metal is suitable for the manufacture of a particular cable.
This is a very important point, since incorrectly selected material can cause a fire as a result of overheating from the passage of excess voltage current.
Silver metal has the highest electrical conductivity. At a temperature of +20 degrees Celsius, it is 63.3 * 104 centimeters-1. But making wiring from silver is very expensive, since it is a rather rare metal, which is used mainly for the production of jewelry and decorative items or bullion coins.
The metal with the highest electrical conductivity among all elements of the base group is copper. Its indicator is 57*104 centimeters-1 at a temperature of +20 degrees Celsius.
Copper is one of the most common conductors used for household and industrial purposes. It withstands constant electrical loads well, is durable and reliable.
The high melting point allows you to work for a long time in a heated state without problems.
In terms of abundance, only aluminum can compete with copper, which ranks fourth in electrical conductivity after gold. It is used in networks with low voltage, as it has almost half the melting point of copper and is not able to withstand extreme loads. The further distribution of places can be found by looking at the table of electrical conductivity of metals.
It is worth noting that any alloy has much lower conductivity than the pure substance. This is due to the merging of the structural network and, as a consequence, disruption of the normal functioning of electrons.
For example, in the production of copper wire, a material with an impurity content of no more than 0.1% is used, and for some types of cable this indicator is even stricter - no more than 0.05%.
All given indicators are the electrical conductivity of metals, which is calculated as the ratio between the current density and the magnitude of the electric field in the conductor.
Classical theory of electrical conductivity of metals
The basic principles of the theory of electrical conductivity of metals contain six points. First: a high level of electrical conductivity is associated with the presence of a large number of free electrons. Second: electric current arises through external influence on the metal, during which electrons move from random motion to ordered motion.
Third: the strength of the current passing through a metal conductor is calculated according to Ohm's law. Fourth: different numbers of elementary particles in the crystal lattice lead to unequal resistance of metals. Fifth: electric current in the circuit arises instantly after the start of exposure to electrons. Sixth: as the internal temperature of the metal increases, the level of its resistance also increases.
The nature of the electrical conductivity of metals is explained by the second point of the provisions. In a quiet state, all free electrons rotate chaotically around the nucleus. At this moment, the metal is not able to independently reproduce electrical charges. But as soon as you connect an external source of influence, the electrons instantly line up in a structured sequence and become carriers of electric current. With increasing temperature, the electrical conductivity of metals decreases.
This is due to the fact that the molecular bonds in the crystal lattice weaken, elementary particles begin to rotate in an even more chaotic order, so the formation of electrons in a chain becomes more complicated.
Therefore, it is necessary to take measures to prevent overheating of the conductors, as this negatively affects their performance properties. The mechanism of electrical conductivity of metals cannot be changed due to the current laws of physics.
But it is possible to neutralize negative external and internal influences that interfere with the normal course of the process.
Metals with high electrical conductivity
The electrical conductivity of alkali metals is at a high level, since their electrons are weakly attached to the nucleus and easily line up in the desired sequence. But this group is characterized by low melting points and enormous chemical activity, which in most cases does not allow their use for the manufacture of wires.
Metals with high electrical conductivity when opened are very dangerous for humans. Touching a bare wire will result in an electrical burn and a powerful discharge to all internal organs. This often results in instant death. Therefore, special insulating materials are used for the safety of people.
Depending on the application, they can be solid, liquid or gaseous. But all types are designed to do one thing—isolating electrical current within a circuit so that it cannot affect the outside world. The electrical conductivity of metals is used in almost all areas of modern human life, so ensuring safety is a top priority.
Source: https://promplace.ru/vidy-metallov-i-klassifikaciya-staty/electroprovodnost-metallov-1479.htm
