What is current: basic characteristics and concepts. What is electric current? Conditions for the existence of electric current: characteristics and actions

". Today I want to touch on such a topic as electric current. What is it? Let's try to remember the school curriculum.

Electric current is the ordered movement of charged particles in a conductor.

If you remember, in order for charged particles to move, (an electric current arises) you need to create an electric field. To create an electric field, you can carry out such elementary experiments as rubbing a plastic handle on wool and for some time it will attract light objects. Bodies capable of attracting objects after rubbing are called electrified. We can say that the body in this state has electric charges, and the bodies themselves are called charged. From the school curriculum, we know that all bodies are made up of tiny particles (molecules). A molecule is a particle of a substance that can be separated from a body and it will have all the properties inherent in this body. Molecules of complex bodies are formed from various combinations of atoms of simple bodies. For example, a water molecule consists of two simple ones: an oxygen atom and one hydrogen atom.

Atoms, neutrons, protons and electrons - what are they?

In turn, an atom consists of a nucleus and revolving around it electrons. Each electron in an atom has a small electrical charge. For example, a hydrogen atom consists of a nucleus of an electron revolving around it. The nucleus of an atom consists, in turn, of protons and neutrons. The nucleus of an atom, in turn, has an electrical charge. The protons that make up the nucleus have the same electric charges and electrons. But protons, unlike electrons, are inactive, but their mass is many times greater than the mass of an electron. The particle neutron, which is part of the atom, has no electric charge, it is neutral. The electrons that revolve around the nucleus of an atom and the protons that make up the nucleus are carriers of equal electric charges. Between the electron and the proton there is always a force of mutual attraction, and between the electrons themselves and between the protons, the force of mutual repulsion. Because of this, the electron has a negative electric charge, and the proton positive. From this we can conclude that there are 2 kinds of electricity: positive and negative. The presence of equally charged particles in an atom leads to the fact that between the positively charged nucleus of the atom and the electrons rotating around it, there are forces of mutual attraction that hold the atom together. Atoms differ from each other in the number of neutrons and protons in the nuclei, which is why the positive charge of the nuclei of atoms of various substances is not the same. In atoms of different substances, the number of rotating electrons is not the same and is determined by the positive charge of the nucleus. The atoms of some substances are firmly bound to the nucleus, while in others this bond can be much weaker. This explains the different strengths of the bodies. Steel wire is much stronger than copper wire, which means that steel particles are more strongly attracted to each other than copper particles. The attraction between molecules is especially noticeable when they are close to each other. The most striking example is that two drops of water merge into one upon contact.

Electric charge

In the atom of any substance, the number of electrons revolving around the nucleus is equal to the number of protons contained in the nucleus. The electric charge of an electron and a proton are equal in magnitude, which means that the negative charge of the electrons is equal to the positive charge of the nucleus. These charges mutually balance each other, and the atom remains neutral. In an atom, electrons create an electron shell around the nucleus. The electron shell and the nucleus of an atom are in continuous oscillatory motion. When the atoms move, they collide with each other and one or more electrons fly out of them. The atom ceases to be neutral and becomes positively charged. Since its positive charge has become more negative (weak connection between the electron and the nucleus - metal and coal). In other bodies (wood and glass), the electronic shells are not broken. After breaking away from atoms, free electrons move randomly and can be captured by other atoms. The process of appearances and disappearances in the body is continuous. As the temperature increases, the speed of the vibrational movement of atoms increases, the collisions become more frequent, become stronger, the number of free electrons increases. However, the body remains electrically neutral, since the number of electrons and protons in the body does not change. If a certain amount of free electrons is removed from the body, then the positive charge becomes greater than the total charge. The body will be positively charged and vice versa. If a lack of electrons is created in the body, then it is additionally charged. If the excess is negative. The greater this deficiency or excess, the greater the electric charge. In the first case (more positively charged particles), bodies are called conductors (metals, aqueous solutions of salts and acids), and in the second (lack of electrons, negatively charged particles) dielectrics or insulators (amber, quartz, ebonite). For the continuous existence of an electric current, it is necessary to constantly maintain a potential difference in the conductor.

Well, that's a little physics course is over. I think you, with my help, remembered the school curriculum for the 7th grade, and we will analyze what the potential difference is in my next article. Until we meet again on the pages of the site.

Without electricity, it is impossible to imagine the life of a modern person. Volts, Amps, Watts - these words are heard in a conversation about devices that run on electricity. But what is this electric current and what are the conditions for its existence? We will talk about this further, providing a brief explanation for beginner electricians.

Definition

An electric current is a directed movement of charge carriers - this is a standard formulation from a physics textbook. In turn, certain particles of matter are called charge carriers. They may be:

• Electrons are negative charge carriers.
• Ions are positive charge carriers.

But where do charge carriers come from? To answer this question, you need to remember the basic knowledge about the structure of matter. Everything that surrounds us is matter, it consists of molecules, its smallest particles. Molecules are made up of atoms. An atom consists of a nucleus around which electrons move in given orbits. Molecules also move randomly. The movement and structure of each of these particles depends on the substance itself and the influence of the environment on it, such as temperature, stress, and so on.

An ion is an atom in which the ratio of electrons and protons has changed. If the atom is initially neutral, then the ions, in turn, are divided into:

• Anions are the positive ion of an atom that has lost electrons.
• Cations are an atom with "extra" electrons attached to the atom.

The unit of current is Ampere, according to it is calculated by the formula:

where U is voltage [V] and R is resistance [Ohm].

Or directly proportional to the amount of charge transferred per unit of time:

where Q is the charge, [C], t is the time, [s].

Conditions for the existence of an electric current

We figured out what electric current is, now let's talk about how to ensure its flow. For electric current to flow, two conditions must be met:

1. The presence of free charge carriers.
2. Electric field.

The first condition for the existence and flow of electricity depends on the substance in which the current flows (or does not flow), as well as its state. The second condition is also feasible: for the existence of an electric field, the presence of different potentials is necessary, between which there is a medium in which charge carriers will flow.

Recall: Voltage, EMF is a potential difference. It follows that in order to fulfill the conditions for the existence of current - the presence of an electric field and an electric current, voltage is needed. These can be plates of a charged capacitor, a galvanic cell, an EMF that has arisen under the influence of a magnetic field (generator).

We figured out how it arises, let's talk about where it is directed. The current, basically, in our usual use, moves in conductors (electrical wiring in an apartment, incandescent bulbs) or in semiconductors (LEDs, your smartphone's processor and other electronics), less often in gases (fluorescent lamps).

So, in most cases, the main charge carriers are electrons, they move from minus (a point with a negative potential) to a plus (a point with a positive potential, you will learn more about this below).

But an interesting fact is that the direction of current movement was taken to be the movement of positive charges - from plus to minus. Although in fact the opposite is happening. The fact is that the decision on the direction of the current was made before studying its nature, and also before it was determined due to which the current flows and exists.

Electric current in different environments

We have already mentioned that in different media the electric current can differ in the type of charge carriers. Media can be divided according to the nature of conductivity (in descending order of conductivity):

1. Conductor (metals).
2. Semiconductor (silicon, germanium, gallium arsenide, etc.).
3. Dielectric (vacuum, air, distilled water).

in metals

Metals contain free charge carriers and are sometimes referred to as "electric gas". Where do free charge carriers come from? The fact is that metal, like any substance, consists of atoms. Atoms somehow move or oscillate. The higher the temperature of the metal, the stronger this movement. At the same time, the atoms themselves generally remain in their places, actually forming the structure of the metal.

In the electron shells of an atom, there are usually several electrons that have a rather weak bond with the nucleus. Under the influence of temperatures, chemical reactions and the interaction of impurities, which are in any case in the metal, electrons are detached from their atoms, positively charged ions are formed. The detached electrons are called free and move randomly.

If an electric field acts on them, for example, if you connect a battery to a piece of metal, the chaotic movement of electrons will become ordered. Electrons from a point to which a negative potential is connected (the cathode of a galvanic cell, for example) will begin to move towards a point with a positive potential.

in semiconductors

Semiconductors are materials in which there are no free charge carriers in the normal state. They are in the so-called forbidden zone. But if external forces are applied, such as an electric field, heat, various radiations (light, radiation, etc.), they overcome the band gap and pass into the free band or the conduction band. Electrons break away from their atoms and become free, forming ions - positive charge carriers.

Positive carriers in semiconductors are called holes.

If you simply transfer energy to a semiconductor, for example, heat it, a chaotic movement of charge carriers will begin. But if we are talking about semiconductor elements, such as a diode or a transistor, then at the opposite ends of the crystal (a metallized layer is applied to them and the leads are soldered), an EMF will appear, but this does not apply to the topic of today's article.

If you apply an EMF source to a semiconductor, then the charge carriers will also move into the conduction band, and their directed movement will also begin - holes will go to the side with a lower electric potential, and electrons - to the side with a larger one.

In vacuum and gas

A vacuum is a medium with a complete (ideal case) absence of gases or a minimized (in reality) its amount. Since there is no matter in vacuum, there is no source for charge carriers. However, the flow of current in a vacuum marked the beginning of electronics and a whole era of electronic elements - vacuum tubes. They were used in the first half of the last century, and in the 50s they began to gradually give way to transistors (depending on the specific field of electronics).

Let's assume that we have a vessel from which all the gas has been pumped out, i.e. it is a complete vacuum. Two electrodes are placed in the vessel, let's call them an anode and a cathode. If we connect the negative potential of the EMF source to the cathode, and positive to the anode, nothing will happen and no current will flow. But if we start heating the cathode, the current will start to flow. This process is called thermionic emission - the emission of electrons from a heated surface of an electron.

The figure shows the process of current flow in a vacuum lamp. In vacuum tubes, the cathode is heated by a nearby filament in Fig. (H), such as that found in a lighting lamp.

At the same time, if you change the polarity of the supply - apply a minus to the anode, and apply a plus to the cathode - the current will not flow. This will prove that the current in vacuum flows due to the movement of electrons from the CATHODE to the ANODE.

A gas, like any substance, consists of molecules and atoms, which means that if the gas is under the influence of an electric field, then at a certain strength (ionization voltage), the electrons will break away from the atom, then both conditions for the flow of electric current will be fulfilled - the field and free media.

As already mentioned, this process is called ionization. It can occur not only from the applied voltage, but also when the gas is heated, x-rays, under the influence of ultraviolet and other things.

Current will flow through the air, even if a burner is installed between the electrodes.

The flow of current in inert gases is accompanied by gas luminescence; this phenomenon is actively used in fluorescent lamps. The flow of electric current in a gaseous medium is called a gas discharge.

in liquid

Let's say that we have a vessel with water in which two electrodes are placed, to which a power source is connected. If the water is distilled, that is, pure and does not contain impurities, then it is a dielectric. But if we add a little salt, sulfuric acid, or any other substance to the water, an electrolyte is formed and a current begins to flow through it.

An electrolyte is a substance that conducts electricity by dissociating into ions.

If copper sulfate is added to water, then a layer of copper will settle on one of the electrodes (cathode) - this is called electrolysis, which proves that the electric current in the liquid is carried out due to the movement of ions - positive and negative charge carriers.

Electrolysis is a physical and chemical process, which consists in the separation of the components that make up the electrolyte on the electrodes.

Thus, copper plating, gilding and coating with other metals occur.

Conclusion

To summarize, for the flow of electric current, free charge carriers are needed:

• electrons in conductors (metals) and vacuum;
• electrons and holes in semiconductors;
• ions (anions and cations) in liquids and gases.

In order for the movement of these carriers to become ordered, an electric field is needed. In simple terms, apply a voltage at the ends of the body or install two electrodes in an environment where an electric current is expected to flow.

It is also worth noting that the current in a certain way affects the substance, there are three types of exposure:

• thermal;
• chemical;
• physical.

Useful

(electron-hole conductivity). Sometimes electric current is also called displacement current, resulting from a change in time of the electric field.

Electric current has the following manifestations:

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Classification

If charged particles move inside macroscopic bodies relative to a particular medium, then such a current is called electric conduction current. If macroscopic charged bodies are moving (for example, charged raindrops), then this current is called convection .

There are direct and alternating electric currents, as well as all kinds of alternating current. In such terms, the word "electric" is often omitted.

• DC Current - current, the direction and magnitude of which do not change with time.

Eddy currents

Eddy currents (Foucault currents) are “closed electric currents in a massive conductor that arise when the magnetic flux penetrating it changes,” therefore, eddy currents are induction currents. The faster the magnetic flux changes, the stronger the eddy currents. Eddy currents do not flow along certain paths in the wires, but, closing in the conductor, form vortex-like contours.

The existence of eddy currents leads to the skin effect, that is, to the fact that the alternating electric current and magnetic flux propagate mainly in the surface layer of the conductor. Eddy current heating of conductors leads to energy losses, especially in the cores of AC coils. To reduce energy losses due to eddy currents, the alternating current magnetic circuits are divided into separate plates, isolated from each other and located perpendicular to the direction of eddy currents, which limits the possible contours of their paths and greatly reduces the magnitude of these currents. At very high frequencies, instead of ferromagnets, magnetodielectrics are used for magnetic circuits, in which, due to the very high resistance, eddy currents practically do not occur.

Characteristics

It is historically accepted that current direction coincides with the direction of movement of positive charges in the conductor. In this case, if the only current carriers are negatively charged particles (for example, electrons in a metal), then the direction of the current is opposite to the direction of movement of charged particles. .

Drift velocity of electrons

Radiation resistance is caused by the formation of electromagnetic waves around the conductor. This resistance is in complex dependence on the shape and dimensions of the conductor, on the wavelength of the emitted wave. For a single rectilinear conductor, in which everywhere the current is of the same direction and strength, and the length of which L is much less than the length of the electromagnetic wave emitted by it λ (\displaystyle \lambda ), the dependence of resistance on wavelength and conductor is relatively simple:

The most used electric current with a standard frequency of 50 Hz corresponds to a wave with a length of about 6 thousand kilometers, which is why the radiation power is usually negligibly small compared to the heat loss power. However, as the frequency of the current increases, the length of the emitted wave decreases, and the radiation power increases accordingly. A conductor capable of radiating appreciable energy is called an antenna.

Frequency

Frequency refers to an alternating current that periodically changes strength and/or direction. This also includes the most commonly used current, which varies according to a sinusoidal law.

An alternating current period is the shortest period of time (expressed in seconds) after which changes in current (and voltage) are repeated. The number of periods completed by the current per unit of time is called the frequency. Frequency is measured in hertz, one hertz (Hz) corresponds to one period per second.

Bias current

Sometimes, for convenience, the concept of displacement current is introduced. In Maxwell's equations, the displacement current is present on an equal footing with the current caused by the movement of charges. The intensity of the magnetic field depends on the total electric current, which is equal to the sum of the conduction current and the displacement current. By definition, the bias current density j D → (\displaystyle (\vec (j_(D))))- vector quantity proportional to the rate of change of the electric field E → (\displaystyle (\vec (E))) in time:

The fact is that with a change in the electric field, as well as with the flow of current, a magnetic field is generated, which makes these two processes similar to each other. In addition, a change in the electric field is usually accompanied by energy transfer. For example, when charging and discharging a capacitor, despite the fact that there is no movement of charged particles between its plates, they speak of a displacement current flowing through it, carrying some energy and closing the electrical circuit in a peculiar way. Bias current I D (\displaystyle I_(D)) in the capacitor is determined by the formula:

where Q (\displaystyle Q)- charge on the capacitor plates, U (\displaystyle U)- potential difference between the plates, C (\displaystyle C) is the capacitance of the capacitor.

Displacement current is not an electric current, because it is not related to the movement of an electric charge.

Main types of conductors

Unlike dielectrics, conductors contain free carriers of uncompensated charges, which, under the action of a force, usually a difference in electrical potentials, set in motion and create an electric current. The current-voltage characteristic (dependence of current strength on voltage) is the most important characteristic of a conductor. For metallic conductors and electrolytes, it has the simplest form: the current strength is directly proportional to the voltage (Ohm's law).

Metals - here the current carriers are conduction electrons, which are usually considered as an electron gas, clearly showing the quantum properties of a degenerate gas.

Plasma is an ionized gas. Electric charge is carried by ions (positive and negative) and free electrons, which are formed under the influence of radiation (ultraviolet, X-ray and others) and (or) heating.

Electrolytes - "liquid or solid substances and systems in which ions are present in any noticeable concentration, causing the passage of an electric current" . Ions are formed in the process of electrolytic dissociation. When heated, the resistance of electrolytes decreases due to an increase in the number of molecules decomposed into ions. As a result of the passage of current through the electrolyte, the ions approach the electrodes and are neutralized, settling on them. Faraday's laws of electrolysis determine the mass of the substance released on the electrodes.

There is also an electric current of electrons in a vacuum, which is used in cathode ray devices.

Electric currents in nature

Electric current is used as a carrier of signals of varying complexity and types in different areas (telephone, radio, control panel, door lock button, and so on).

In some cases, unwanted electric currents appear, such as stray currents or short circuit current.

The use of electric current as a carrier of energy

• obtaining mechanical energy in various electric motors,
• obtaining thermal energy in heating devices, electric furnaces, during electric welding,
• obtaining light energy in lighting and signaling devices,
• excitation of electromagnetic oscillations of high frequency, ultrahigh frequency and radio waves,
• receiving sound,
• obtaining various substances by electrolysis, charging electric batteries. This is where electromagnetic energy is converted into chemical energy.
• creating a magnetic field (in electromagnets).

The use of electric current in medicine

• diagnostics - the biocurrents of healthy and diseased organs are different, while it is possible to determine the disease, its causes and prescribe treatment. The branch of physiology that studies electrical phenomena in the body is called electrophysiology.
  • Electroencephalography is a method for studying the functional state of the brain.
  • Electrocardiography is a technique for recording and studying electric fields during the work of the heart.
  • Electrogastrography is a method for studying the motor activity of the stomach.
  • Electromyography is a method for studying bioelectric potentials that occur in skeletal muscles.
• Treatment and resuscitation: electrical stimulation of certain areas of the brain; treatment of Parkinson's disease and epilepsy, also for electrophoresis. A pacemaker that stimulates the heart muscle with a pulsed current is used for bradycardia and other cardiac arrhythmias.

electrical safety

It includes legal, socio-economic, organizational and technical, sanitary and hygienic, medical and preventive, rehabilitation and other measures. Electrical safety rules are regulated by legal and technical documents, regulatory and technical framework. Knowledge of the basics of electrical safety is mandatory for personnel servicing electrical installations and electrical equipment. The human body is a conductor of electric current. Human resistance with dry and intact skin ranges from 3 to 100 kOhm.

The current passed through the human or animal body produces the following actions:

• thermal (burns, heating and damage to blood vessels);
• electrolytic (blood decomposition, violation of the physico-chemical composition);
• biological (irritation and excitation of body tissues, convulsions)
• mechanical (rupture of blood vessels under the action of steam pressure obtained by heating with blood flow)

The main factor determining the outcome of electric shock is the amount of current passing through the human body. According to safety engineering, electric current is classified as follows:

• safe a current is considered, the long passage of which through the human body does not harm him and does not cause any sensations, its value does not exceed 50 μA (alternating current 50 Hz) and 100 μA direct current;
• minimally perceptible human alternating current is about 0.6-1.5 mA (alternating current 50 Hz) and 5-7 mA direct current;
• threshold relentless called the minimum current of such a force at which a person is no longer able to tear his hands away from the current-carrying part by an effort of will. For alternating current, this is about 10-15 mA, for direct current - 50-80 mA;
• fibrillation threshold is called an alternating current (50 Hz) of about 100 mA and 300 mA of direct current, the effect of which is longer than 0.5 s with a high probability of causing fibrillation of the heart muscles. This threshold is simultaneously considered conditionally lethal for humans.

In Russia, in accordance with the Rules for the technical operation of electrical installations of consumers and the Rules for labor protection during the operation of electrical installations, 5 qualification groups for electrical safety have been established, depending on the qualifications and experience of the employee and the voltage of electrical installations.

2. Under what conditions does an electric current occur?

3. Why is the motion of charged particles in a conductor in the absence of an external electric field chaotic?

4. What is the difference between the motion of charged particles in a conductor in the absence and in the presence of an external electric field?

5. How is the direction of the electric current chosen? In what direction do electrons move in a metal conductor through which an electric current flows?

Current and voltage are quantitative parameters used in electrical circuits. Most often, these values ​​​​change over time, otherwise there would be no point in the operation of the electrical circuit.

Voltage

Conventionally, the voltage is indicated by the letter U. The work done to move a unit of charge from a point of low potential to a point of high potential is the voltage between these two points. In other words, this is the energy released after the transition of a unit of charge from a high potential to a small one.

Voltage can also be called the potential difference, as well as the electromotive force. This parameter is measured in volts. To move 1 coulomb of charge between two points that have a voltage of 1 volt, you need to do 1 joule of work. Coulombs measure electric charges. 1 pendant is equal to the charge of 6x10 18 electrons.

Voltage is divided into several types, depending on the types of current.

• Constant pressure . It is present in electrostatic circuits and DC circuits.
• AC voltage . This type of voltage is available in circuits with sinusoidal and alternating currents. In the case of a sinusoidal current, voltage characteristics such as:
  voltage fluctuation amplitude is its maximum deviation from the x-axis;
  instant voltage, which is expressed at a certain point in time;
  operating voltage, is determined by the active work of the 1st half-cycle;
  medium rectified voltage, determined by the modulus of the rectified voltage for one harmonic period.

When transmitting electricity through overhead lines, the arrangement of supports and their dimensions depend on the magnitude of the applied voltage. The voltage between phases is called line voltage , and the voltage between ground and each of the phases is phase voltage . This rule applies to all types of overhead lines. In Russia, in household electrical networks, the standard is a three-phase voltage with a linear voltage of 380 volts, and a phase voltage value of 220 volts.

Electricity

The current in an electrical circuit is the speed of electrons at a certain point, measured in amperes, and is indicated on the diagrams by the letter " I". Derived units of the ampere are also used with the appropriate prefixes milli-, micro-, nano, etc. A current of 1 ampere is generated by moving a unit of charge of 1 coulomb in 1 second.

Conventionally, it is considered that the current flows in the direction from the positive potential to the negative one. However, from the course of physics it is known that the electron moves in the opposite direction.

You need to know that the voltage is measured between 2 points on the circuit, and the current flows through one specific point of the circuit, or through its element. Therefore, if someone uses the expression "voltage in resistance", then this is incorrect and illiterate. But often we are talking about voltage at a certain point in the circuit. This refers to the voltage between ground and this point.

Voltage is formed from the impact on electrical charges in generators and other devices. Current is generated by applying voltage to two points in a circuit.

To understand what current and voltage are, it would be more correct to use. On it you can see the current and voltage, which change their values ​​over time. In practice, the elements of an electrical circuit are connected by conductors. At certain points, the circuit elements have their own voltage value.

Current and voltage obey the rules:

• The sum of the currents entering the point is equal to the sum of the currents leaving the point (charge conservation rule). Such a rule is Kirchhoff's law for current. The point of entry and exit of current in this case is called a node. A consequence of this law is the following statement: in a series electrical circuit of a group of elements, the current for all points is the same.
• In a parallel circuit of elements, the voltage across all elements is the same. In other words, the sum of voltage drops in a closed circuit is zero. This Kirchhoff's law applies to stresses.
• The work done per unit time by the circuit (power) is expressed as follows: P \u003d U * I. Power is measured in watts. 1 joule of work done in 1 second is equal to 1 watt. Power is distributed in the form of heat, is spent on mechanical work (in electric motors), is converted into radiation of various types, accumulates in tanks or batteries. When designing complex electrical systems, one of the challenges is the thermal load of the system.

Electric current characteristic

A prerequisite for the existence of current in an electrical circuit is a closed circuit. If the circuit breaks, then the current stops.

Everything in electrical engineering works on this principle. They break the electrical circuit with moving mechanical contacts, and this stops the flow of current, turning off the device.

In the energy industry, electric current occurs inside current conductors, which are made in the form of tires, and other parts that conduct current.

There are also other ways to create an internal current in:

• Liquids and gases due to the movement of charged ions.
• Vacuum, gas and air using thermionic emission.
• due to the movement of charge carriers.

Conditions for the occurrence of electric current

• Heating conductors (not superconductors).
• Application to charge carriers of potential difference.
• Chemical reaction with the release of new substances.
• The effect of a magnetic field on a conductor.

Current Waveforms

• Straight line.
• Variable harmonic sine wave.
• A meander that looks like a sine wave, but has sharp corners (sometimes the corners can be smoothed).
• A pulsating form of one direction, with an amplitude that fluctuates from zero to the largest value according to a certain law.

Types of work of electric current

• Light emitted by lighting devices.
• Generating heat with heating elements.
• Mechanical work (rotation of electric motors, action of other electrical devices).
• Creation of electromagnetic radiation.

Negative phenomena caused by electric current

• Overheating of contacts and current-carrying parts.
• The occurrence of eddy currents in the cores of electrical devices.
• Electromagnetic radiation to the external environment.

The creators of electrical devices and various circuits when designing must take into account the above properties of electric current in their designs. For example, the harmful effect of eddy currents in electric motors, transformers and generators is reduced by blending the cores used to transmit magnetic fluxes. Core blending is its manufacture not from a single piece of metal, but from a set of separate thin plates of special electrical steel.

But, on the other hand, eddy currents are used to operate microwave ovens, ovens, operating on the principle of magnetic induction. Therefore, we can say that eddy currents are not only harmful, but also beneficial.

An alternating current with a signal in the form of a sinusoid can vary in frequency of oscillation per unit of time. In our country, the industrial current frequency of electrical devices is standard, and is equal to 50 hertz. In some countries, the current frequency is 60 hertz.

For various purposes in electrical engineering and radio engineering, other frequency values ​​\u200b\u200bare used:

• Low frequency signals with lower current frequency.
• High frequency signals, which are much higher than the current frequency of industrial use.

It is believed that electric current occurs when electrons move inside a conductor, so it is called conduction current. But there is another type of electric current, which is called convection. It occurs when charged macrobodies move, for example, raindrops.

Electric current in metals

The movement of electrons under the influence of a constant force on them is compared with a parachutist who descends to the ground. In these two cases, uniform motion occurs. The force of gravity acts on the skydiver, and the force of air resistance opposes it. The electric field force acts on the movement of electrons, and the ions of the crystal lattices resist this movement. The average speed of the electrons reaches a constant value, as does the speed of the skydiver.

In a metal conductor, the speed of one electron is 0.1 mm per second, and the speed of an electric current is about 300,000 km per second. This is because electric current flows only where voltage is applied to the charged particles. Therefore, a high current flow rate is achieved.

When moving electrons in a crystal lattice, there is the following regularity. The electrons do not collide with all the oncoming ions, but only with every tenth of them. This is explained by the laws of quantum mechanics, which can be simplified as follows.

The movement of electrons is hindered by large ions that resist. This is especially noticeable when metals are heated, when heavy ions "swing", increase in size and reduce the electrical conductivity of the crystal lattices of the conductor. Therefore, when metals are heated, their resistance always increases. As the temperature decreases, the electrical conductivity increases. By reducing the temperature of the metal to absolute zero, the effect of superconductivity can be achieved.