Talks on Electrical Engineering: Electricity - from simple to complex. Part 2.

English physicist Michael Faraday suggested a different approach. He introduced the concept in physics electric field. What it allowed, as they believed, to completely abandon the "action at a distance" in physics. According to Faraday, the charges do not interact with each other directly. Each of them creates an electric field in the space, whose value (or voltage) decreases with increasing distance from the charge. The effect of this charge is transferred to the space from point to point by means of an electric field. This view is known as the theory of short-range.

Modern electrophysics is based on this theory. But note that to date, there are very subtle experimental facts, which work on the revival of the long-range theory. However, to talk about them we are not going to ... The science of electricity is divided into electrostatics and electrodynamics. The first studies the interaction of electric charges through purely electric fields.

II (electrodynamics) - is the science of interaction between moving electric charges with the electromagnetic field, or rather, electromagnetic effects, arising from the movement of electric charges in any metals or vacuum. It is here that we encounter the phenomenon of the flow of electric current in a closed circuit.

What is the electric current in metals? Since the nucleus of atoms of metals are massive, they remain in the crystal lattice and the electrons (both very mobile and "light") move freely in the interior of the crystal. This refers to the peripheral electrons, which are very poorly connected electrical forces with .dalekim. atomic nucleus. And so it is sufficient to power a small surplus, so they left their atom and began to migrate within the crystal lattice.

As soon as an electron leaves the atom, he immediately becomes positively charged. And a free electron from among those that move freely within the crystal, immediately takes a "position." The atom becomes neutral again, but not for long ...

Note that the electrons within the crystal move randomly, and their speed is quite high. It depends largely on the temperature of the crystal. At room temperature, the average electron velocity is a few meters per second.

A lot or a little? If we take into account the size of the electron, and relate them to move the value committed to them for a second, this ratio is impressive, for example, in an ordinary CRT, an electron speed reaches tens of thousands of kilometers per second! But it in vacuo. Now, to visualize the length of wire, such as copper (Figure 1).

Here, the free electrons are depicted as circles, provided with arrows. These arrows representing vectors, illustrate the fact that the average speed of free electrons at a given temperature is approximately the same, which is not the direction of (electron) movement.

It has a disordered, chaotic. This means that for a certain unit of time, for example, for one second, the number of electrons that cross-sectional plane of the wire (marked as 2) in the direction from right to left, and those that are for the same time cross-section is the same LEFT TO RIGHT!

In this case, it holds the following conclusion: despite the fact that a large number of free electrons is a continual movement within the crystal structure of the metal, no current NO! And now we introduce into the picture for a change (Figure 2) above.

EACH free electron appeared some additional component of the average speed, which is indicated in Figure 2 by the dashed arrows. In its absolute value, these arrows (vector) is ten times smaller than the average vectors of chaotic speed. But they all act in unison in the same direction. Since the rule of vector addition, the average velocity of the electrons, which move from left to right, will be higher than the average velocity of the electrons, which move from right to left! And as in this case, there is no equality between the number of electrons that pass through the section plane in the opposite direction, then we may say that in this case there is an electric current! In the idealized figures 1 and 2 (so as not to clutter the picture) is shown only six electrons.

Let us remember that the electric current can have two completely different mechanisms. In fact, imagine that, for example, in the open space of any metallic object gets into force of any third-party cause of some electric charge (for example, negative) comes up to another piece of metal that has or excess charge there are no or it is opposite in sign. In addition, let the first object has a structure similar to that shown in Figure 3.

Then at the moment of contact items 1 and 2 of the excess charge of the electrons will be distributed between them in such a way that the concentrations become equal. However, since the electrons will flow from one to two through the rod, which is built in ammeter, then, naturally, the latter will record the electric current. The magnitude of this current will have no permanent and exponential, as shown in Figure 4. Here is an example that the electric current can flow in the open circuit.

Incidentally, the initial value of the current can reach enormous values, for example, when lightning strikes a metallic object. An entirely different mechanism of the phenomenon takes place in a closed circuit. Electrical engineering and electronics is based on the functioning of closed circuits.

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