In the space around an electrically charged body, there is an electric

A field that is one of the types of matter. Electric field possesses energy, which manifests itself in the form of forces acting on charged bodies in the field.

The electric field is conventionally depicted as ley lines, which are directed in the direction in which a positively charged particle would move in the field.

Field strength... The electric field acts on the charge introduced into it q (fig. 4) with some force F ... Therefore, about the intensity electric field can be judged by the value of the force with which a certain electric charge is attracted or repulsed. In electrical engineering, field intensity is characterized by electric field strength E, which is understood as the relation of power F acting on a charged body at a given point of the field, to the charge q of this body:

E \u003d F / q

As the distance from the charged body increases, the lines of force of the electric field are located less frequently, i.e., the field strength E decreases (Fig. 3, a, b and c). Only in a uniform electric field (Fig. 3d) is the strength the same at all its points.

Electrical potential . An electric field has a certain amount of energy, that is, the ability to perform work, which can be realized if any charge is introduced into it. This charge will move in the direction of the lines of force, doing some work. To characterize the energy stored at each point of the electric field, a special concept is introduced - electrical potential. Electrical potential φ fields at a given point equal to work, which the forces of this field can perform when the unit moves positive charge from that point out of the field.

For the zero potential, the potential that the earth's surface has is conventionally taken.

Electrical voltage.Different points of the electric field have different potentials. Usually we are of little interest in the absolute value of the potentials of individual points of the electric field, it is more important to know the potential difference φ 1 -φ 2 between two points of the field AND and B (fig. 5). Potential difference φ 1 and φ 2 two points of the field characterizes the work spent by the field forces to move the charge from one point of the field with a large potential to another - a point with a lower potential and is called electric

voltage. Electric voltage is indicated by the letter U .

Unit electrical voltage serves Volt (V).

Similar information:

1. A. Body impulse. B. Impulse of power. B. Kinetic energy. D. Potential energy. E. Double kinetic energy
2. A. Voltage. B. Current strength. B. Electromotive force. D. Specific electrical resistance. D. Electrical resistance
3. A. Potential of the electric field. B. Electric field strength. B. Electrical voltage. D. Electric capacity
4. A. Potential energy. B. Work. B. Power. D. Pressure. D. Efficiency
5. A. Current strength. B. Voltage. B. Electrical resistance. D. Specific electrical resistance. D. Electromotive force

In the space around an electrically charged body, there is an electric

A field that is one of the types of matter. An electric field has energy, which manifests itself in the form of forces acting on charged bodies in the field.

An electric field is conventionally depicted in the form of lines of force, which are directed in the direction in which a positively charged particle would move in the field.

Field strength... The electric field acts on the charge introduced into it q (fig. 4) with some force F ... Consequently, the intensity of the electric field can be judged by the value of the force with which a certain electric charge is attracted or repulsed. In electrical engineering, field intensity is characterized by electric field strength E, which is understood as the relation of power F acting on a charged body at a given point of the field, to the charge q of this body:

E \u003d F / q

As the distance from the charged body increases, the lines of force of the electric field are located less frequently, i.e., the field strength E decreases (Fig. 3, a, b and c). Only in a uniform electric field (Fig. 3d) is the strength the same at all its points.

Electrical potential . An electric field has a certain amount of energy, that is, the ability to perform work, which can be realized if any charge is introduced into it. This charge will move in the direction of the lines of force, doing some work. To characterize the energy stored at each point of the electric field, a special concept is introduced - electrical potential. Electrical potential φ field at a given point is equal to the work that the forces of this field can perform when moving a unit of positive charge from this point outside the field.

For the zero potential, the potential that the earth's surface has is conventionally taken.

Electrical voltage.Different points of the electric field have different potentials. Usually we are of little interest in the absolute value of the potentials of individual points of the electric field, it is more important to know the potential difference φ 1 -φ 2 between two points of the field AND and B (fig. 5). Potential difference φ 1 and φ 2 two points of the field characterizes the work spent by the field forces to move the charge from one point of the field with a large potential to another - a point with a lower potential and is called electric

voltage. Electric voltage is indicated by the letter U .

The unit of electrical voltage is Volt (V).

Work on moving electric charge

Let's calculate the work when moving an electric charge in a uniform electric field with intensity. If the charge moved along the line of field strength at a distance (Fig. 134), then the work is

A \u003d F e(d 1- d 2) = qE(d 1- d 2), (39.1)

where d 1 and d 2 - distances from start and end points to plate IN.
In mechanics, it was shown that when moving between two points in a gravitational field, the work of gravity does not depend on the trajectory of the body. The forces of gravitational and electrostatic interaction have the same dependence on the distance, the force vectors are directed along a straight line connecting the interacting point bodies. It follows from this that when a charge moves in an electric field from one point to another, the work of the electric field forces does not depend on the trajectory of its motion.
This conclusion is confirmed by the most accurate experiments.
When the direction of movement is changed by 180 °, the work of the forces of the electric field, like the work of the force of gravity, changes its sign to the opposite. If when moving the charge q from point IN exactly FROM the forces of the electric field did the work AND, then when moving the charge q along the same path from point FROM exactly IN they do the work - AND... But since the work does not depend on the trajectory, then when moving along the trajectory CKBwork is done too - AND... Hence it follows that when the charge moves first from the point IN exactly FROMand then from point FROM exactly IN, that is, along a closed trajectory, the total work of the forces of the electrostatic field turns out to be zero (Fig. 135).

The work of the forces of the electrostatic field when the electric charge moves along any closed path is zero.
A field whose work of forces along any closed trajectory is equal to zero is called potential field. Gravitational and electrostatic field are potential fields.

Potential and voltage in an electric field

For energy performance each point of the electric field introduces the concept of "potential". The potential is indicated by the letter φ.

The potential at each point of the electric field is characterized by the energy W, which is spent (or can be spent) by the field to move a unit of positive charge q from a given point outside the field, if the field is created by a positive charge, or from outside the field to a given point, if the field created by a negative charge (Fig. 1.7a).

From the above definition it follows that the potential at point A is equal to φ A= W A / q; at point B - W B / q, and the potential at point C is W C / q.

The potential is measured in volts [ φ ] \u003d \u003d J / Kl \u003d V.

The magnitude of the potential at each point of the electric field is determined by the expression

φА \u003d(1.12)

Potential - scalar... If an electric field is created by several charges, then the potential at each point of the field is determined by the algebraic sum of the potentials created at this point by each charge.

Since (Fig. 1.7a) r А< r В < r С, то из (1.12) следует, что φ А > φ В\u003e φ С, if the field is created by a positive charge.

If a positive test charge is placed at point A (Fig. 1.7a) of the electric field, then under the action of the field forces it will move from point A to point B, and then to point C, i.e. in the direction of the field. Thus, the positive test charge moves from a point of high potential to a point of lower potential. The charge will not move between points with equal potentials. Therefore, to move the charge between two points of the electric field, there must be a potential difference at these points.

The potential difference between two points of an electric field characterizes the voltage between these points.

U AB \u003d φ A - φ B; U BC \u003d φ B - φ C; U АС \u003d φ А - φ C

The voltage between two points of the electric field is characterized by the energy expended to move a unit of positive charge between these points, i.e. U AB \u003d W AB / q

The voltage is measured in volts (V).

There is a relationship between voltage and intensity in a uniform electric field (Fig. 1.8)

U AB \u003d φ A - φ B \u003d W AB / q = Fl / q \u003d El,

whence follows

E \u003d U AB / l . (1.13)

It can be seen from this formula that the strength of a uniform electric field is determined by the ratio of the voltage between two points of the field to the distance between these points.

The unit of electric field strength is V / m (volt per meter).

The potentials at the points of the electric field have different meanings. However, in an electric field, a number of points with the same potential can be distinguished. The surface passing through these points is called equipotential or equipotential. An example of such a surface are the plates of a cylindrical capacitor (Fig. 1.7b) and a flat capacitor (Fig. 1.9). They have the same potential over the entire area of \u200b\u200beach plate and are equipotential surfaces.

3. Electricity - this is the phenomenon of directional movement of carriers electric charges and (or) the phenomenon of changes in the electric field in time, accompanied by magnetic field... In metal conductors and in vacuum (under certain conditions), the current is formed by an electron flow, and in liquids and gases - by a flow of ions and electrons.

Bodies that conduct electricity well are called CONDUCTORS.

Conductors.Very often electrons (especially those that are weakly bound to the nucleus of an atom) can leave their orbit, go into interatomic space. These electrons are called free. Substances, in the interatomic space of which there are always free electrons, are classified as conductors of the first kind. and the current in the conductor is created by free electrons. These include all metals. In practice, these are wires, cable cores, relay contacts, e-wires. lamps, etc.

Solutions of acids, salts and alkalis (electrolytes) are classified as conductors of the second kind. Positive and negative ions are continuously formed in the electrolyte. The electric current in the electrolyte is created not by free electrons, but by ions.

4. Electromotive force (EMF) - scalar physical quantitycharacterizing the work of third-party (non-potential) forces in sources of constant or alternating current... In a closed conducting circuit, the EMF is equal to the work of these forces to move a single positive charge along the circuit.

EMF can be expressed through the strength of the electric field of external forces (). In a closed loop () then the EMF will be equal to:

Where is the element of the contour length.

EMF, like voltage, is measured in volts. You can talk about electromotive force on any part of the chain. This is the specific work of external forces not in the entire circuit, but only in this area. The EMF of a galvanic cell is the work of external forces when a single positive charge moves inside the cell from one pole to another. The work of external forces cannot be expressed through the potential difference, since external forces are non-potential and their work depends on the shape of the trajectory. So, for example, the work of external forces when the charge moves between the current terminals outside the source itself is zero.

Volt-ampere characteristics (VAC) - a graph of the dependence of the current through a two-terminal device on the voltage at this two-terminal device. The current-voltage characteristic describes the behavior of a two-terminal device on a constant current. Most often, the CVC of nonlinear elements is considered (the degree of nonlinearity is determined by the nonlinearity coefficient), since for linear elements the CVC is a straight line and is not of particular interest.

Typical examples of elements with a substantially nonlinear I - V characteristic: diode, thyristor, zener diode.

For three-pole elements (such as a transistor, thyristor or tube triode), families of curves are often built, which are the I – V characteristics for a two-pole device with one way or another given the parameters at the third output of the element.

It should be noted that in a real circuit, especially one that operates at relatively high frequencies (close to the boundaries of the operating frequency range) for a given device, the real dependence of voltage on time can run along trajectories that are very far from the "ideal" I - V characteristic. Most often this is due to the capacity or other inertial properties of the element.

5. Job electric current shows what work has been done by the electric field when the charges move along the conductor.

The work of an electric current is equal to the product of current strength and voltage
and for the duration of the current in the circuit.

The unit for measuring the work of electric current in the SI system:
[A] \u003d 1 J \u003d 1A. B. c

The power of the electric current shows the work of the current, performed per unit of time
and is equal to the ratio of the work done to the time during which this work was done.

(power in mechanics is usually denoted by the letter N, in electrical engineering - the letter R)
because A \u003d IUt, then the power of the electric current is:

The unit of power of electric current in the SI system:

[P] \u003d 1 W (watt) \u003d 1 A. B

6. The simplest electrical circuit (Fig. 12) contains a source electrical energy G, energy receiver P and two line wires L 1 and L 2connecting the source to the receiver of energy. Line wires are connected to a source of electrical energy using two terminals called positive (+) and negative (-) poles.

A source of electrical energy converts mechanical, chemical, thermal or other type of energy into electrical energy. The receiver converts electrical energy into energy of a different type - mechanical, thermal, chemical, light, etc.

Sources of electrical energy are generators (electrical machines driven by any mechanical motors), batteries and galvanic cells, the symbol of which is shown in Fig. 13. Lighting lamps, electric motors, electric heaters, etc. are used as receivers of electrical energy.

Both galvanic cells and batteries are interconnected to form, in the first case, a battery of galvanic cells, and in the second - a battery of accumulators. A source of electrical energy with linear wires connected to it and an energy receiver form a closed electrical circuit, along which there is a continuous movement of electricity, called electric current.

D.C in metal conductors is a steady forward motion of free electrons in a closed circuit.

The strength of the current flowing in two conductors spaced at a certain distance from each other causes mechanical forces acting on these conductors. The unit for measuring current is ampere ( and). In the International System of Units (SI) ampere- the force of the constant current, which, passing through two parallel straight conductors infinite length and negligible round sectionlocated at a distance of 1 m one from the other in a vacuum, would cause a force between these conductors equal to 2 · 10 -7 Newtons ( n) for each meter of length.

The unit of force in the International System of Units is newton (n); n= ,

where kg - kilogram of mass,

m -meter,

sec -second.

Electricity determines the amount of electricity flowing through the cross section of a conductor per unit of time. If a current of 1 A flows in a conductor, then 1 k of electricity flows through the cross section of this conductor for 1 sec.

With current in the conductor I during t through the cross-section of this conductor, an amount of electricity flows equal to

This dependence is valid for the case when during the time t the current strength remains unchanged.

Line wires and the energy receiver make up an external circuit in which the current flows under the action of a potential difference at the terminals of the energy source and is directed from a point of higher potential (positive terminal) to a point of lower potential (negative terminal)

Ohm's law for a chain section and is written in the following form:

This expression reads as follows: current is directly proportional to voltage and inversely proportional to resistance.

You should know that:

I is the value of the current flowing through the section of the circuit;

U is the value of the applied voltage to the section of the circuit;

R is the resistance value of the considered section of the circuit.

Using Ohm's law for a section of a circuit, you can calculate the applied voltage to a section of the circuit (Figure 1), or the voltage at the input terminals of the circuit (Figure 2).

Figure 2. Series circuit illustrating the calculation of the voltage at the terminals of the circuit.

In this case, formula (1) will take the following form:

U \u003d I * R

But it is necessary to know the current and resistance of the circuit section.

The third version of Ohm's law for a section of a circuit, which allows calculating the resistance of a section of a circuit using known values \u200b\u200bof current and voltage, is as follows:

7. When the conductors are connected in series, the current strength in all conductors is the same. When connected in series, all the elements are connected to each other so that the circuit section that includes them does not have a single node.

In the space around an electrically charged body, there is an electric

field, which is one of the types of matter. An electric field has energy, which manifests itself in the form of forces acting on charged bodies in the field.

E

an electric field is conventionally depicted in the form of lines of force that are directed in the direction in which a positively charged particle would move in the field.

H field strength... The electric field acts on the charge introduced into it q (fig. 4) with some force F ... Consequently, the intensity of the electric field can be judged by the value of the force with which a certain electric charge is attracted or repulsed. In electrical engineering, field intensity is characterized by electric field strength E, which is understood as the relation of power F acting on a charged body at a given point of the field, to the charge q of this body:

E = F / q

As the distance from the charged body increases, the lines of force of the electric field are located less frequently, i.e., the field strength E decreases (Fig. 3, a, b and c). Only in a uniform electric field (Fig. 3d) is the strength the same at all its points.

Electrical potential. An electric field has a certain amount of energy, that is, the ability to perform work, which can be realized if any charge is introduced into it. This charge will move in the direction of the lines of force, doing some work. To characterize the energy stored at each point of the electric field, a special concept is introduced - electrical potential. Electrical potential φ field at a given point is equal to the work that the forces of this field can perform when moving a unit of positive charge from this point outside the field.

For the zero potential, the potential that the earth's surface has is conventionally taken.

E

electrical voltage.Different points of the electric field have different potentials. Usually we are of little interest in the absolute value of the potentials of individual points of the electric field, it is more important to know the potential difference φ 1 -φ 2 between two points of the field AND and B (fig. 5). Potential difference φ 1 and φ 2 two points of the field characterizes the work spent by the field forces to move the charge from one point of the field with a large potential to another - a point with a lower potential and is called electric

voltage. Electric voltage is indicated by the letter U .

The unit of electrical voltage is Volt (V).

3. Electric current and electrical conductivity of a substance.

In a substance placed in an electric field, a process of directed movement of elementary carriers of electricity arises. The charged particles are electrons or ions. The movement of these electrically charged particles is called electric shock.

The unit of current is Ampere (A)... This is such a current at which an amount of electricity equal to 1 cl... In the formulas, the current is denoted by the letter I .

In electrical engineering, both direct and alternating current are widely used. Constant is the current, the value and direction of which at any time remain unchanged (Fig. 6, a). Currents, the value and direction of which do not remain constant, are called changing, or variables.

The property of a substance to conduct an electric current under the action of an electric field is called electrical conductivity... The electrical conductivity of various substances depends on the concentration of free electrically charged particles. The more there are, the greater the electrical conductivity of a given substance. All substances, depending on their electrical conductivity, are divided into three groups: conductors, dielectrics (insulating materials) and semiconductors.

The high electrical conductivity of metals is explained by the electronic theory of the structure of the atom, according to which the atoms of metals have such a structure in which the electrons in the last electronic orbit are relatively weakly bound to the nuclei of atoms. Therefore, they freely move between atoms, passing from one to another and filling the space between them. These electrons are called free .

If you introduce a metal conductor into an electric field, then free electrons under the action of the field forces will begin to move towards the positive pole, creating an electric current. Thus, an electric current in metal conductors is called an ordered (directed) movement of free electrons.