Electric voltage. What is current and voltage with simple words

Instruction

The electrical voltage is measured by voltmeters that are divided into millivoltmeters, voltmeters, kilovoltmeters, etc.

Three-phase networks

The entire planet power system is based on three-phase network. It carries two voltage types: linear and phase. Linear network voltage is a voltage between two conductors, and the phase is between the conductor and the neutral wire or zero. Therefore, when we connect the load on the triangular scheme, the linear voltage becomes equal to the phase, and when we connect the load according to the "Star" scheme, then the linear voltage increases to the root of three times. Hence the designations of the three-phase network, as 220/380 in or 127/220 V. The first number indicates a phase voltage, and the second is on linear.
For a general idea of \u200b\u200bthe values \u200b\u200bof electrical voltage on various objects, we give them.

Voltage on some objects

The voltage between the electrodes when the electrocardiogram is removed - 1-2 mV.
Palching battery - 1.5 V.
Telephone line - 60 V.
Electric eel - 650 V.
High-frequency television antenna - from 1 to 100 mV.
Contacts of the tram line - 550 V.
The thunderstorm cloud is 10 gigavolts.

When the torn wire concerns the Earth, stepper voltage may occur. Until a certain point, it is not very dangerous. It becomes fatal only when the path of electricity movement in the human body is changing.

Stepper voltage - the tension of one person. Feet are contacts, and the current moves along a closed foot chain. This is a dangerous state, but not fatal, since the scale part of electricity passes through the heart. If the current leads to uncontrolled muscle contractions and a person will fall, the passage path will change and step tension will increase. This is a deadly situation. In no case should it be allowed. To do this, it is necessary to leave the danger zone quickly, but very small chains, since the stepper voltage is directly proportional to the distance between the contact points. But it is better to jump on one leg from the lesion zone.

Electrical voltage - this is energy characteristic electric field. The voltage is numerically equal to the ratio of work on the movement of the charged particle q to the size of the charge of this particle.

If one pendant value was made to move the value of one joule, the magnitude of the electrical voltage was made - one volt. Volt is a unit of voltage measurement on the international system SI. Named in honor of Alessandro Volta, who opened the world's first source electrical Energy (galvanic cell).

About electrical voltage sometimes speak as a difference in potentials. Suppose that the potential of one field point is 5 pendant, and the second point of the field 10 pendant. The voltage between the two points will be equal to the potential difference of two points 10 cl - 5 cl \u003d 5 V.

To record the voltage values \u200b\u200boften use kilovolts (1 kV \u003d 1000 V), malelvolts (1 mV \u003d 0.001 V). Less often occurs the value of megavolt (1 mV \u003d 1000 kV), gigavolts (1 gv \u003d 1000 mV), as well as microvolt (1 μV \u003d 0.001 mV) and nanovolt (1 H \u003d 0.001 μV). As a rule, in electrical installations to the operating voltage to 1000 V to designate the parameter, volts are used, and in electrical installations above 1000 V - kilovolts. To determine the voltage value, special electrical meters are used - voltmeters. Depending on the value of the voltage measured, in addition to voltmeters, Millivoltmeters and kilovoltmeters are used.

Electrical voltage in three-phase network

The basis of our entire power system is a three-phase network. In a three-phase network, two types of electrical stress distinguish: linear and phase. Linear network voltage is the voltage between the two linear wires of the three-phase network. Phase voltage network - voltage value between the beginning and end of one of three phases electrical network, that is, the voltage between the linear wire and neutral (zero) wire. When connecting the load of consumers according to the "triangle" scheme, the linear voltage is equal to the network voltage. When connecting electrical energy consumers according to the "Star" scheme, a linear voltage to the root of three more phase. For example, linear voltage is 380 volts, and the phase voltage is 220 volts.

The voltage in the three-phase network is made to designate a fraction in which the numerator is a phase voltage of the network, and the denominator is a linear voltage of the network. For example, 127/220 B, 220/380 V, 380/660 V.

There is a generally accepted range of standard (nominal) voltage values \u200b\u200bin a three-phase electrical network:

In electrical installations up to 1000 in: 127, 220, 380, 660 V. - in electrical installations above 1000 volts: 3, 6, 10, 20, 35, 110, 150, 220, 330, 500 square meters. Significant exceeding the standards of the nominal voltage value is called.

Nominal values \u200b\u200bof electrical voltage of some objects

(Object, type and voltage value):

electrocardiogram: impulse, 1-2 mV;
finger Battery: Permanent, 1.5 V;
aerial television: high-frequency, 1-100 mV;
croon Battery: Permanent, 9 V;
nutrition Laptop: Permanent, 12 V;
telephone line: Permanent, 60 V;
the discharge of an electrical eel: constant, 650 V;
electric Scope Date: Permanent, 250 V;
contact system tram: constant, 550 V;
church of Russia: A variable 220/380 V;
uS electricity: A variable 110/190 V;
japan's power grid: variable 100/172 V.
the thunderstorm cloud: constant, up to 10 gv. (10 gigavolt \u003d 10000000000 volts !!!)

Before considering the concept of voltage electric currentBriefly remark the concept of current at all. In very general concept - This is an ordered, directional motion of charged particles (electrons), produced under the influence of the electric field. You can also not forget about the strength of the current - one of the main values \u200b\u200bof electricity. When moving charges electric field Makes a certain job.

Principle of voltage operation

Than greater charge must be moved in 1 second in electrical chainThe greater work is performed by an electric field. Therefore, its work is completely dependent on. However, in addition to the strength of the current, there is another value that affects the work. This will be the tension that will be discussed.

The voltage is the ratio of the current operation on the segment of the chain to the size of the charge passing through this section of the electrical circuit. In other words, this is the work (energy) consumed when moving one positive charge From a point with a small potential to a point with great potential. The voltage is defined as a difference in potentials or electromotive power.

Unit of measurement of electric current is Joule (J), electric charge Measured in the coulons (CL). Thus, the voltage measurement unit is 1 J / CL. This unit was called Volt (B), in honor of Alessandro Giuseppe Antonio Anastasio Volta (1745-1827) - Italian scientist physics and chemist, one of the founders of electricity doctrine.

How this unit is working in practice

If you explain simply, for the uninitiated, the volt will be considered a measure of "pressure" or the impact that causes the electric current to move around the chain or wire. At the same time, the amp will be its measure "volume". To clearly explain the work of Volta and Ampere, as an example, you can use the principle of "water in the hose". Here, the voltage in volts will be similar to the pressure of water, and the force in amperes is the volume of water. If water enters the hose without a tip, then a large amount of water passes through it (), the pressure occurs a small (volt). When we press the tip of the hose with a finger, the volume of water passing on it decreases, but the water pressure increases and the jet splashes much further.

Comparing this example with electricity, we see that the current of the current is the number of electrons passing through the wire, and the voltage shows us, with what force these electrons are pushing. It follows from this that with the same voltage at the wire, conducting larger electrical current must be larger diameter.

To occur in the voltage in the electrical network, some kind of current source is required. When the electrical circuit is in an open state, the voltage exists only on the terminals of the source itself. When the current source is turned on in the electrical circuit, voltage occurs in separate areas. Simultaneously in the circuit there is a strength of the current. We observe the relationship: without voltage - there is no current strength.

To measure the voltage, a special electrical measuring device is used, which is called a voltmeter. In its appearance, it is practically similar to, and differs only by the scale. On the scale of the ammeter - the letter "A", at the Voltmeter - the letter "V". When performing measurements, the ammeter is turned on in a circuit sequentially, and a voltmeter-parallel.

This is passing through the conductor electrons carrying negative charge. The volume of this charge or, in other words, the amount of electricity characterizes current strength. We know that the current is the same in all places of the chain.

Electrons can not disappear or "jump off" from wires and load. Therefore, current strength we can measure in any place of the electrical circuit. However, will the same current effect on different sections of this chain? Let's figure it out.

Passing along the wires, the current is only slightly heats them, but it does not make a lot of work. Passing through the spiral of the light bulb, the current does not just heats it strongly, it heats it to such an extent that she, raving, starts glowing. That is, in this case, the current performs mechanical work, and quite a decent work. Clean spends its energy. Electrons in the same quantity continue to run on, but they already have less energy.

Determination of electrical stress

That is, the electric field was to "drag" electrons through the load, and the energy that was spent, characterized by the value called electric voltage. The same energy has spent some change in the state of the load of the load. Energy, as we know, does not disappear to nowhere and does not appear from nowhere. This is a law of energy conservation. That is, if the current spent the energy to pass through the load, the load acquired this energy and, for example, heated.

That is, we come to definition: electric current voltage - This is the value showing what work the field has made when the charge is moving from one point to another. The voltage in different parts of the chain will be different. The voltage on the portion of the empty wire will be very small, and the voltage on the plot with any load will be much large, and the voltage value will depend on the value of the operation produced by the current. Measure voltage in volts (1 V). To determine the voltage, there is a formula:

where u is tension,
A - work performed by a current to move the charge Q to a certain section of the chain.

Voltage on the Poles of the current source

As for the voltage on the plot of the chain - everything is clear. And what then means tension on the poles? In this case, this voltage means the potential value of the energy that the source can give the current. It is like water pressure in the pipes. This amount of energy that will be spent if you connect some load to the source. Therefore, the greater the voltage at the current source, the greater work can be made.

Voltmeter

To measure the voltage, there is a device called a voltmeter. Unlike the ammeter, it is not connected arbitrarily anywhere in the chain, but parallel to the load, before it is after. In this case, the voltmeter shows the voltage applied to the load. To measure the voltage on the poles of the current source, the voltmeter is connected directly to the instrument poles.

That is, the electric field was to "drag" electrons through the load, and the energy that was spent, characterized by an electrical voltage. The same energy has spent some change in the state of the load of the load. Energy, as we know, does not disappear to nowhere and does not appear from nowhere. About this read Law of energy conservation. That is, if the current spent the energy to pass through the load, the load acquired this energy and, for example, heated.

where U is the voltage, A is the work performed by the current to move the charge Q to a certain section of the chain.

Voltage on the Poles of the current source

As for the voltage on the plot of the chain - everything is clear. And what then means tension on the poles current source? In this case, this voltage means the potential value of the energy that the source can give the current. It is like water pressure in the pipes. This amount of energy that will be spent if you connect some load to the source. Therefore, the greater the voltage at the current source, the greater work can be made.

2) dielectrics in the electric field

Unlike conductors, there are no free charges in dielectrics. All charges are

related: electrons belong to their atoms, and solid dielectric ions fluctuate

near the crystal lattice nodes.

Accordingly, when placing a dielectric in the electric field does not arise a directed movement of charges

Therefore, for dielectrics do not pass our evidence properties.

conductors - after all, all these arguments relied on the possibility of current appearance. And acting, none of the four properties of conductors formulated in the previous article,

it does not spread to dielectrics.

2. The volumetric charge density in the dielectric can be different from zero.

3. Voltage lines may not be perpendicular to the surface of the dielectric.

4. Different dielectric points may have different potential. Became to talk about

The "dielectric potential" does not have.

Polarization of dielectrics - phenomenon associated with limited displacement related charges In a dielectric or rotation of electric dipoles, usually under the influence of an external electric field, sometimes under the action of other external strength or spontaneously.

Polarization of dielectrics characterizes vector of electric polarization. The physical meaning of the electric polarization vector is a dipole moment, referred to a unit volume of a dielectric. Sometimes the polarization vector is briefly called simply polarization.

Polarization vector is applicable to describing the macroscopic state of polarization not only conventional dielectrics, but also ferroelectrics, and, in principle, any media with similar properties. It is applicable not only to describe induced polarization, but also spontaneous polarization (in ferroelectrics).

Polarization is a dielectric state, which is characterized by the presence of an electrical dipole moment in any (or almost anyone) element of its volume.

There are polarization induced in a dielectric under the action of an external electric field, and spontaneous (spontaneous) polarization, which occurs in ferroelectrics in the absence of an external field. In some cases, the polarization of the dielectric (ferroelectric) occurs under the action of mechanical stresses, friction forces or due to temperature change.

Polarization does not change the total charge in any macroscopic volume inside a homogeneous dielectric. However, it is accompanied by the appearance of connected electrical charges on its surface with some surface density σ. These related charges are created in dielectric an additional macroscopic field with a voltage directed against the external field with tension. As a result, the field strength inside the dielectric will be expressed by the equality:

Depending on the polarization mechanism, the polarization of dielectrics can be divided into the following types:

Electronic - displacement of electronic shells of atoms under the action of an external electric field. The fastest polarization (up to 10 -15 s). Not related to losses.

Ionic - displacement of the assemblies of the crystal structure under the action of an external electric field, and the displacement by a value smaller than the magnitude of the lattice. The flow time is 10 -13 s, without loss.

Dipole (orientational) - proceeds with losses to overcome communication forces and internal friction. Related to the orientation of dipoles in an external electric field.

Electron-relaxation - orientation of defective electrons in an external electric field.

Ion-relaxation - ion shift, weakly fixed in the nodes of the crystal structure, or in the interruption.

Structural - orientation of impurities and inhomogeneous macroscopic inclusions in the dielectric. The slowest type.

Spontaneous (spontaneous) - due to this type of polarization in dielectrics, which is observed, the polarization exhibits substantially nonlinear properties even at small values \u200b\u200bof the external field, the phenomenon of hysteresis is observed. Dielectrics (ferroelectrics) are characterized by very high dielectric constant values \u200b\u200b(from 900 to 7500 in some types of condenser ceramics). The introduction of spontaneous polarization, as a rule, increases the tangent of the corner of the material loss (up to 10 -2)

Resonant - orientation of particles, whose own frequencies coincide with the frequencies of the external electric field.

Migration polarization is due to the presence of layers in the material with different conductivity, the formation of volumetric charges, especially at high voltage gradients, has large losses and is the polarization of the slow motion.

Polarization of dielectrics (with the exception of resonant) is maximum in static electric fields. In variable fields, due to the presence of inertia electrons, ions and electric dipoles, the vector of electrical polarization depends on the frequency.