What is the name of the phenomenon of occurrence. The phenomenon of electromagnetic induction

The date: 07.05.2021

Electromagnetic induction was discovered by Michael Faraday on August 29, 1831. He found that the electromotive force generated in a closed conductive loop is proportional to the rate of change of the magnetic flux through the surface bounded by this loop. The magnitude of the electromotive force (EMF) does not depend on what is the cause of the change in flux - a change in the magnetic field itself or the movement of the circuit (or part of it) in a magnetic field. The electric current caused by this EMF is called induction current.

Being instantaneous, instantly disappearing after their appearance, inductive currents would have no practical value if Faraday had not found a way, using an ingenious device (switch), to continually interrupt and re-conduct the primary current flowing from the battery along the first wire, due to which the second wire is continuously excited more and more inductive currents, thus becoming constant. So a new source of electrical energy was found, in addition to the previously known (friction and chemical processes) - induction, and a new type of this energy - induction electricity.

IN 1820 Hans Christian Oersted showed that the electric current flowing through the circuit causes the magnetic needle to deflect. If electric current generates magnetism, then the appearance of electric current must be associated with magnetism. This thought captured the English scientist M. Faraday... “Convert magnetism into electricity,” he wrote in 1822 in his diary. For many years he persistently set up various experiments, but unsuccessfully, and only August 29, 1831 a triumph came: he discovered the phenomenon of electromagnetic induction. The setup on which Faraday made his discovery was that Faraday made a ring of soft iron about 2 cm wide and 15 cm in diameter and wound many turns of copper wire on each half of the ring. The circuit of one winding was closed by a wire, in its turns there was a magnetic needle, far removed so that the effect of the magnetism created in the ring did not affect. A current from a battery of galvanic cells was passed through the second winding. When the current was turned on, the magnetic needle made several oscillations and calmed down; when the current was interrupted, the needle oscillated again. It turned out that the arrow deviated in one direction when the current was turned on and in the other when the current was interrupted. M. Faraday established that "converting magnetism into electricity" can be done with the help of an ordinary magnet.

POWER LINES are lines drawn in any force field ( cm. FORCE FIELD) (electric, magnetic, gravitational), the tangents to which at each point of the field coincide in direction with the vector characterizing the given field (the vector of intensity ( cm. ELECTRIC FIELD STRENGTH) electric or gravitational fields, the vector of magnetic induction ( cm. MAGNETIC INDUCTION)). Lines of force are only a visual way of depicting force fields. For the first time the concept of "lines of force" for electric and magnetic fields was introduced by M. Faraday ( cm. FARADAY Michael).
Since field strengths and magnetic induction are single-valued functions of a point, only one line of force can pass through each point in space. The density of the lines of force is usually chosen so that the number of lines of force crossing a unit area perpendicular to the lines of force is proportional to the field strength (or magnetic induction) at that area. Thus, the lines of force give a clear picture of the distribution of the field in space, characterizing the magnitude and direction of the field strength.
The lines of force of the electrostatic field ( cm. ELECTROSTATIC FIELD) are always open: they start at positive charges and end at negative ones (or go to infinity). The lines of force do not intersect anywhere, since at each point of the field its intensity has one single value and a definite direction. The density of the field lines is greater near charged bodies, where the field strength is greater.
The lines of force of the electric field in the space between two positive charges diverge; you can specify a neutral point at which the fields of repulsive forces of both charges extinguish each other.
The lines of force of a single charge are radial straight lines that radiate from the charge in beams, like the lines of force of the gravitational field of a point mass or a ball. The farther from the charge, the less dense the lines - this illustrates the weakening of the field with increasing distance.
The lines of force emanating from a charged conductor of irregular shape thicken near any protrusion or tip, near concavities or cavities the density of the lines of force decreases.
If the lines of force come from a positively charged tip located near a negatively charged flat conductor, then they condense around the tip, where the field is very strong, and diverge into a large region near the plane, on which they end, entering the plane perpendicularly.
The electric field in the space between the parallel charged plates is uniform. The lines of tension in a uniform electric field are parallel to each other.
If a particle, for example an electron, enters the force field, then it acquires acceleration under the action of the force field, and the direction of its motion cannot exactly follow the direction of the lines of force, it will move in the direction of the momentum vector.
A magnetic field ( cm. A MAGNETIC FIELD) characterize the lines of magnetic induction, at any point of which the vector of magnetic induction is tangential.
The lines of magnetic induction of the magnetic field of a straight conductor with current are circles lying in planes perpendicular to the conductor. The centers of the circle are on the axis of the conductor. The lines of force of the vector of magnetic induction are always closed, that is, the magnetic field is vortex. Iron filings placed in a magnetic field line up along the lines of force; due to this, it is possible to experimentally determine the form of the lines of force of magnetic induction. The vortex electric field generated by the changing magnetic field also has closed lines of force.

Maxwell laid the foundations for modern classical electrodynamics (Maxwell's equations), introduced the concepts of bias current and electromagnetic field, received a number of consequences from his theory (prediction electromagnetic waves, electromagnetic nature Sveta, light pressure and others). He is one of the founders kinetic theory of gases, established the velocity distribution of gas molecules ( Maxwell distribution). Maxwell was one of the first to introduce statistical concepts into physics, showed the statistical nature second law of thermodynamics(« Maxwell's demon"), Received a number of important results in molecular physics and thermodynamics(Maxwell's thermodynamic relations, Maxwell's rule for the liquid-gas phase transition, and others). He is the pioneer of the quantitative theory of colors, the author of the principle color photography... Maxwell's other work includes studies on stability rings of Saturn, elasticity theory and mechanics ( photoelasticity, Maxwell's theorem), optics, mathematics. He prepared manuscripts for publication Henry Cavendish, paid a lot of attention popularization of science, designed a number of scientific instruments.

Experimental confirmation by Hertz of Maxwell's theory
The first experimental confirmation of Maxwell's electromagnetic theory was given in the experiments of Hertz in 1887, eight years after Maxwell's death. To obtain electromagnetic waves, Hertz used a device consisting of two rods separated by a spark gap (Hertz vibrator). At a certain potential difference in the gap between them, a spark appeared - a high-frequency discharge, current oscillations were excited and an electromagnetic wave was emitted. To receive waves, Hertz used a resonator - a rectangular contour with a gap, at the ends of which small copper balls are fixed.
The experiment also managed to measure the speed of electromagnetic waves, which turned out to be equal to the speed of light in a vacuum. These results are one of the strongest proofs of the correctness of Maxwell's electromagnetic theory, according to which light is an electromagnetic wave.

№29????

1 Einstein's postulate or the principle of relativity: all laws of nature are invariant with respect to all inertial frames of reference. All physical, chemical, biological phenomena occur in all inertial reference systems in the same way.

The postulate or principle of the constancy of the speed of light: the speed of light in a vacuum is constant and the same in relation to any inertial reference frames. It does not depend on the speed of the light source or on the speed of its receiver. No material object can move at a speed exceeding the speed of light in a vacuum. Moreover, pi is one particle of matter, i.e. a particle with a rest mass other than zero cannot reach the speed of light in a vacuum; only field particles can move at this speed, i.e. particles with zero rest mass.

Space-time (space-time continuum) is a physical model that complements space with equal temporal dimensions and, thus, creates a theoretical-physical structure, which is called the space-time continuum.

According to the theory of relativity, the Universe has three spatial dimensions and one time dimension, and all four dimensions are organically linked into a single whole, being almost equal and (within certain limits, see the notes below), capable of transforming into each other when the observer changes the system countdown.

Within the framework of the general theory of relativity, space-time also has a single dynamic nature, and its interaction with all other physical objects (bodies, fields) is gravity. Thus, the theory of gravity within the framework of general relativity is a theory of space-time (assumed in it not flat, but capable of dynamically changing its curvature).

Space-time is continuous and from a mathematical point of view it is a manifold, which is usually endowed with the Lorentzian metric.

The phenomenon of the appearance of an electric current in a closed conducting circuit when the magnetic flux covered by this circuit changes is called electromagnetic induction.

It was discovered by Joseph Henry (observations made in 1830, results published in 1832) and Michael Faraday (observations made and results published in 1831).

Faraday's experiments were carried out with two coils inserted into each other (the outer coil is permanently connected to the ammeter, and the inner one, through a key, to the battery). The induction current in the outer coil is observed:

but

When closing and opening the circuit of the inner coil, which is stationary relative to the outer one (Fig. A);

When moving the inner coil with direct current relative to the outer one (Fig. B);

When moving relative to the external coil of the permanent magnet (Fig. C).

Faraday showed that in all cases of induction current in the outer coil, the magnetic flux through it changes. In fig. the outer coil is shown as one turn. In the first case (Fig. A), when the circuit is closed, a current flows through the inner coil, a magnetic field arises (changes) and, accordingly, a magnetic flux through the outer coil. In the second (Fig. B) and third (Fig. C) cases, the magnetic flux through the outer coil changes due to a change in the process of movement of the distance from it to the inner coil with current, or to a permanent magnet.

but

In 1834, Emiliy Khristianovich Lenz experimentally established a rule that allows one to determine the direction of the induction current: the induction current is always directed so as to counteract the cause that causes it; the induction current always has such a direction that the increment of the magnetic flux created by it and the increment of the magnetic flux that caused this induction current are opposite in sign. This rule is called the Lenz rule.

The law of electromagnetic induction can be formulated as follows: the emf of the electromagnetic induction in the circuit is equal to the rate of change with time of the magnetic flux through the surface bounded by this circuit, taken with a minus sign

Here dФ = is the scalar product of the magnetic induction vector and the vector of the surface area. Vector, where is the unit vector () of the normal to an infinitesimal part of the surface with an area.

The minus sign in the expression is associated with the rule for choosing the direction of the normal to the contour that bounds the surface, and the positive direction of walking along it. In accordance with the definition, the magnetic flux Ф through a surface with an area S

depends on time, if changes with time: surface area S;

modulus of the vector of magnetic induction B; angle between vectors and normal .

If a closed loop (coil) consists of turns, then the total flux through the surface bounded by such a complex loop is called flux linkage and is defined as

where Ф i is the magnetic flux through the i loop. If all turns are the same, then

where Ф is the magnetic flux through any loop. In this case

N turns

1 turn

2 turns

The expression allows you to determine not only the magnitude, but also the direction of the induction current. If the values of the emf and, consequently, the induction current, are positive values, then the current is directed along the positive direction of bypassing along the contour, if negative - in the opposite direction (the direction of the positive bypass is determined when choosing the normal to the surface bounded by the contour)

Test 11-1 (electromagnetic induction)

Option 1

1. Who discovered the phenomenon of electromagnetic induction?

BUT. X. Oersted. B. Sh. Coulomb. V. A. Volta. G.A. Amper. D. M. Faraday. E . D. Maxwell.

2. The leads of the copper wire coil are connected to a sensitive galvanometer. In which of the above experiments will the galvanometer detect the occurrence of EMF of electromagnetic induction in the coil?

A permanent magnet is removed from the coil.

The permanent magnet rotates around its longitudinal axis inside the coil.

A. Only in case 1. B. Only in case 2. C. Only in case 3. D. In cases 1 and 2. E. In cases 1, 2 and 3.

3. What is the name of the physical quantity equal to the product of the modulus B of the induction of the magnetic field by the area S of the surface penetrated by the magnetic field, and the cosine
angle a between the induction vector B and the normal n to this surface?

A. Inductance. B. Magnetic flux. B. Magnetic induction. D. Self-induction. D. Energy of the magnetic field.

4. Which of the following expressions determines the EMF of induction in a closed loop?

A. B. IN. G. D.

5. When the strip magnet is pushed into and out of the metal ring, an induction current is generated in the ring. This current creates a magnetic field. Which pole is the current magnetic field in the ring to: 1) the retractable north pole of the magnet and 2) the retractable north pole of the magnet.

6. What is the name of the unit for measuring magnetic flux?

7. The unit of measurement of which physical quantity is 1 Henry?

A. Induction of magnetic field. B. Electrical capacity. B. Self-induction. D. Magnetic flux. D. Inductance.

8. What expression determines the connection of the magnetic flux through the circuit with the inductance L circuit and amperage I in the loop?

A. LI . B. IN. LI ‘ . G. LI 2 . D.

9. What expression determines the relationship between the EMF of self-induction and the current in the coil?

BUT. B . IN . LI . G . . D. LI ‘ .

10. The properties of the various fields are listed below. Which of them does the electrostatic field have?

Tension lines are not associated with electric charges.

The field has energy.

The field has no energy.

BUT. 1, 4, 6. B. 1, 3, 5. IN. 1, 3, 6. G. 2, 3, 5. D. 2, 3, 6. E. 2, 4, 6.

11. A contour with an area of 1000 cm 2 is in a uniform magnetic field with an induction of 0.5 T, the angle between the vector IN

BUT. 250Wb. B. 1000 Wb. IN. 0.1 Wb. G. 2,5 · 10 -2 Wb. D. 2.5 Wb.

12. What is the current in the loop with an inductance of 5 mH creates a magnetic flux 2· 10 -2 Wb?

A. 4 mA. B. 4 A. C. 250 A. D. 250 mA. D. 0.1 A. E. 0.1 mA.

13. The magnetic flux through the loop in 5 · 10 -2 s has uniformly decreased from 10 mWb to 0 mWb. What is the value of the EMF in the circuit at this time?

A. 5 · 10 -4 V. B. 0.1 V. V. 0.2 V. G. 0.4 V. D. 1 V. E. 2 C.

14. What is the value of the energy of the magnetic field of a coil with an inductance of 5 H with a current in it of 400 mA?

A. 2 J. B. 1 J. W. 0.8 J. G. 0.4 J. D. 1000 J. E. 4 10 5 J.

15. A coil containing n turns of wire is connected to a direct current source with voltage U at the exit. What is the maximum value of the EMF of self-induction in the coil when the voltage at its ends increases from 0 V to U IN?

A, U B, B. nU V.V. U /NS U ,

16. Two identical lamps are included in the direct current source circuit, the first in series with the resistor, the second in series with the coil. In which of the lamps (Fig. 1), when the key K is closed, the current will reach its maximum value later than the other?

A. In the first. B. In the second. B. In the first and second at the same time. D. In the first, if the resistance of the resistor is greater than the resistance of the coil. E. In the second, if the resistance of the coil is greater than the resistance of the resistor.

17. A coil with an inductance of 2 H is connected in parallel with a resistor with an electrical resistance of 900 ohms, the current in the coil is 0.5 A, and the electrical resistance of the coil is 100 ohms. What electrical charge will flow in the coil and resistor circuit when they are disconnected from the current source (Fig. 2)?

A. 4000 Cl. B. 1000 cl. H. 250 Cl. G. 1 10 -2 Cl. D. 1.1 10 -3 Cl. E. 1 10 -3 Cl.

18. The plane flies at a speed of 900 km / h, the modulus of the vertical component of the induction vector of the Earth's magnetic field is 4 10 5 T. What is the potential difference between the ends of the wings of an airplane if the wingspan is 50 m?

A. 1.8 C. B. 0.9 C. C. 0.5 C. G. 0.25 C.

19. What should be the current in the armature winding of the electric motor so that a force of 120 N acts on a section of the winding of 20 turns 10 cm long, located perpendicular to the induction vector in a magnetic field with an induction of 1.5 T?

A. 90 A. B. 40 A. C. 0.9 A. G. 0.4 A.

20. What force must be applied to the metal bridge for its uniform movement at a speed of 8 m / s along two parallel conductors located at a distance of 25 cm from each other in a uniform magnetic field with an induction of 2 T? The induction vector is perpendicular to the plane in which the rails are located. The conductors are shorted with a 2 ohm resistor.

A. 10000 N. B. 400 N. V. 200 N. H. 4 N. D. 2 N. E. 1 N. N.

Test 11-1 (electromagnetic induction)

Option 2

1. What is the name of the phenomenon of the appearance of an electric current in a closed loop when the magnetic flux through the loop changes?

A. Electrostatic induction. B. Phenomenon of magnetization. B. Ampere Force. D. Lorentz force. D. Electrolysis. E. Electromagnetic induction.

A permanent magnet is inserted into the coil.

The coil is put on a magnet.

3) The coil rotates around the magnet located
inside her.

A. In cases 1, 2 and 3. B. In cases 1 and 2. C. Only in case 1. D. Only in case 2. E. Only in case 3.

3. Which of the following expressions determines the magnetic flux?

A. BScosα. B. IN. qvBsinα. G. qvBI. D. IBlsina .

4. What does the following statement express: the EMF of induction in a closed loop is proportional to the rate of change of the magnetic flux through the surface bounded by the loop?

A. The law of electromagnetic induction. B. Lenz's Rule. B. Ohm's law for a complete circuit. D. The phenomenon of self-induction. E. The law of electrolysis.

5. When the strip magnet is pushed into and out of the metal ring, an induction current is generated in the ring. This current creates a magnetic field. Which pole is the current magnetic field in the ring to: 1) the retractable south pole of the magnet and 2) the retractable south pole of the magnet.

A. 1 - north, 2 - north. B. 1 - southern, 2 - southern.

B. 1 - south, 2 - north. G. 1 - north, 2 - south.

6. The unit of measurement of which physical quantity is 1 Weber?

A. Magnetic field induction. B. Electrical capacity. B. Self-induction. D. Magnetic flux. D. Inductance.

7. What is the name of the unit for measuring inductance?

A. Tesla. B. Weber. W. Gauss. G. Farad. D. Henry.

8. What expression determines the relationship of the energy of the magnetic flux in the circuit with the inductance L circuit and amperage I in the loop?

BUT . ... B . . IN . LI 2 , G . LI ‘ . D . LI.

9.What is the physical quantity NS defined by the expression x = for coil from NS turns .

A. EMF of induction. B. Magnetic flux. B. Inductance. D. EMF of self-induction. D. Energy of the magnetic field. E. Magnetic induction.

10. The properties of the various fields are listed below. Which of them does the vortex induction electric field have?

Tension lines are necessarily associated with electric charges.

Tension lines are not associated with electrical charges.

The field has energy.

The field has no energy.

The work of forces to move an electric charge along a closed path may not be equal to zero.

The work of forces to move an electric charge along any closed path is zero.

A. 1, 4, 6. B. 1, 3, 5. C. 1, 3, c. G. 2, 3, 5. D. 2, 3, 6. F. 2, 4, 6.

11. The contour with an area of 200 cm 2 is in a uniform magnetic field with an induction of 0.5 T, the angle between the vector IN induction and normal to the surface of the contour 60 °. What is the magnetic flux through the circuit?

A. 50 Vb. B. 2 · 10 -2 Wb. V. 5 · 10 -3 Wb. G. 200 Wb. D. 5 Vb.

12. A current of 4 A creates a magnetic flux of 20 mVb in the loop. What is the inductance of the loop?

A. 5 Mr. B. 5 mH. H. 80 G. G. 80 mH. D. 0.2 G. E. 200 G.

13. The magnetic flux through the loop in 0.5 s decreased uniformly from 10 mWb to 0 mWb. What is the value of the EMF in the circuit at this time?

A. 5 · 10 -3 V. B. 5 V. V. 10 V. G. 20 V. D. 0.02 V. E. 0.01 V.

14. What is the value of the energy of the magnetic field of a coil with an inductance of 500 mH with a current in it of 4 A?

A. 2 J. B. 1 J. W. 8 J. G. 4 J. D. 1000 J. E. 4000 J.

15. Coil containing NS turns of wire, connected to a direct current source with voltage U at the exit. What is the maximum value of the EMF of self-induction in the coil when the voltage at its ends decreases from U V to 0 V?

A. U V. B. nU V.V. U / n V.G.May be many times more U , depends on the rate of change of the current strength and on the inductance of the coil.

16. In the electrical circuit shown in Figure 1, four keys 1, 2, 3 and 4 closed. Opening which of the four will give the best opportunity to detect the phenomenon of self-induction?

BUT. 1. B. 2. B. 3.G. 4. E. Any of the four.

17. A coil with an inductance of 2 H is connected in parallel with a resistor with an electrical resistance of 100 ohms, the current in the coil is 0.5 A, and the electrical resistance of the coil is 900 ohms. What electrical charge will flow in the coil and resistor circuit when they are disconnected from the current source (Fig. 2)?

A. 4000 Cl. B. 1000 cl. H. 250 Cl. G. 1 10 -2 Cl. D. 1.1 10 -3 Cl. E. 1 10 -3 Cl.

18. The plane flies at a speed of 1800 km / h, the modulus of the vertical component of the induction vector of the Earth's magnetic field is 4 10 -5 T. What is the potential difference between the ends of the wings of an airplane if the wingspan is 25 m?

A. 1.8 V. V. 0.5 V. V. 0.9 V. H. 0.25 V.

19. Rectangular frame with an areaS with currentI placed in magnetic induction fieldIN . What is the moment of force acting on the frame, if the angle between the vectorIN and the normal to the frame is a?

A. IBS sin a. B. IBS. IN. IBS cos a. G. I 2 BS sin a. D. I 2 BS cos a. ...

Option 2

Charge in motion. It can take the form of a sudden discharge of static electricity such as lightning. Or it could be a controlled process in generators, batteries, solar or fuel cells. Today we will consider the very concept of "electric current" and the conditions for the existence of an electric current.

Electric Energy

Most of the electricity we use comes in the form of alternating current from the electrical grid. It is created by generators operating according to Faraday's law of induction, thanks to which a changing magnetic field can induce an electric current in a conductor.

Generators have spinning coils of wire that pass through magnetic fields as they rotate. As the coils rotate, they open and close relative to the magnetic field and create an electric current that changes direction at each turn. The current goes through a full cycle forward and backward 60 times per second.

The generators can be powered by steam turbines fueled by coal, natural gas, oil, or a nuclear reactor. From the generator, the current passes through a series of transformers, where its voltage rises. The diameter of the wires determines the amount and amperage they can carry without overheating and wasting energy, and the voltage is limited only by how well the lines are insulated from ground.

It is interesting to note that only one wire carries current, not two. Its two sides are designated as positive and negative. However, because AC polarity changes 60 times per second, they also have other names — hot (mains) and grounded (underground to complete a circuit).

Why do you need electric current?

There are many ways to use electric current: it can light up your home, wash and dry your clothes, open your garage door, make the water in your kettle boil, and enable other household items that make our life so much easier to work. Nevertheless, the ability of the current to transmit information is becoming more and more important.

When connecting to the Internet, a computer uses only a small part of the electric current, but this is something without which a modern person cannot imagine his life.

Electric current concept

Like a river flow, a flow of water molecules, an electric current is a flow of charged particles. What is it that causes it, and why does it not always go in the same direction? When you hear the word "flows", what do you think of? Perhaps it will be a river. This is a good association because it is for this reason that the electric current gets its name. It is very similar to the flow of water, only instead of water molecules moving along the channel, charged particles move along a conductor.

Among the conditions necessary for the existence of an electric current, there is a point providing for the presence of electrons. The atoms in a conductive material have many of these free charged particles that float around and between atoms. Their movement is random, so there is no flow in any given direction. What does it take for an electric current to exist?

The conditions for the existence of an electric current include the presence of voltage. When it is applied to a conductor, all free electrons will move in the same direction, creating a current.

Curious about electric shock

Interestingly, when electrical energy is transmitted through a conductor at the speed of light, the electrons themselves move much more slowly. In fact, if you walked slowly next to a conductive wire, your speed would be 100 times faster than electrons are moving. This is due to the fact that they do not need to travel huge distances in order to transfer energy to each other.

Direct and alternating current

Today, two different types of current are widely used - direct current and alternating current. In the first, electrons move in one direction, from the "negative" side to the "positive". The alternating current pushes the electrons back and forth, changing the direction of the flow several times per second.

Generators used in power plants to generate electricity are designed to produce alternating current. You probably never noticed that the lights in your house actually flicker as the current direction changes, but this happens too quickly for the eyes to recognize.

What are the conditions for the existence of a constant electric current? Why do we need both types and which one is better? These are good questions. The fact that we still use both types of current suggests that they both serve specific purposes. Back in the 19th century, it was clear that efficient transmission of power over long distances between the power plant and the home was only possible at very high voltages. But the problem was that sending really high voltage was extremely dangerous to humans.

The solution to this problem was to relieve stress outside the home before sending it inside. To this day, direct electric current is used for long-distance transmission, mainly because of its ability to readily convert to other voltages.

How does electric current work

The conditions for the existence of an electric current include the presence of charged particles, a conductor, and a voltage. Many scientists have studied electricity and found that there are two types of electricity: static and current.

It is the second that plays a huge role in the daily life of any person, since it is an electric current that passes through the circuit. We use it daily to power our homes and more.

What is Electric Current?

When electrical charges circulate in a circuit from one place to another, an electric current is generated. The conditions for the existence of an electric current include, in addition to charged particles, the presence of a conductor. Most often this is a wire. Its circuit is a closed loop in which the current flows from the power source. When the circuit is open, he cannot complete the path. For example, when the light in your room is off, the circuit is open, but when the circuit is closed, the light is on.

Power current

The conditions for the existence of an electric current in a conductor are greatly influenced by such a voltage characteristic as power. It is a measure of how much energy is being used over a period of time.

There are many different units that can be used to express this characteristic. However, electrical power is almost measured in watts. One watt is equal to one joule per second.

Electric charge in motion

What are the conditions for the existence of an electric current? It can take the form of a sudden discharge of static electricity, such as lightning or a spark from rubbing against a woolen cloth. More often, however, when we talk about electric current, we mean a more controlled form of electricity, thanks to which lights are lit and appliances work. Most of the electrical charge is carried by negative electrons and positive protons inside the atom. However, the latter are mainly immobilized inside atomic nuclei, so the work of transferring charge from one place to another is done by electrons.

Electrons in a conductive material such as a metal are largely free to move from one atom to another along their conduction bands, which are the higher electron orbits. Sufficient electromotive force or voltage creates a charge imbalance that can cause electrons to move through the conductor as an electric current.

If we draw an analogy with water, then take, for example, a pipe. When we open the valve at one end to allow water to enter the pipe, then we do not need to wait for this water to work all the way to its end. We get water at the other end almost instantly because the incoming water pushes the water that is already in the pipe. This is what happens in the case of an electric current in a wire.

Electric current: conditions for the existence of electric current

An electric current is usually viewed as a stream of electrons. When the two ends of the battery are connected to each other with a metal wire, this charged mass through the wire travels from one end (electrode or pole) of the battery to the opposite. So, let's call the conditions for the existence of an electric current:

Charged particles.
Conductor.
Voltage source.

However, not all so simple. What conditions are necessary for the existence of an electric current? This question can be answered in more detail by considering the following characteristics:

Potential difference (voltage). This is one of the prerequisites. There must be a potential difference between the 2 points, meaning that the repulsive force generated by charged particles in one place must be greater than their force at another point. Voltage sources are generally not found in nature, and electrons are distributed fairly evenly throughout the environment. Yet scientists have succeeded in inventing certain types of devices where these charged particles can accumulate, thereby creating the very necessary voltage (for example, in batteries).
Electrical resistance (conductor). This is the second important condition that is necessary for the existence of an electric current. This is the path along which charged particles travel. Only those materials act as conductors that allow electrons to move freely. Those who do not have this ability are called insulators. For example, a metal wire would be an excellent conductor, while its rubber sheath would be an excellent insulator.

Having carefully studied the conditions for the emergence and existence of electric current, people were able to tame this powerful and dangerous element and direct it for the benefit of mankind.