Initially, people did not know what the current. It was known static charge, but no one understood, and was not aware of the nature of electricity. It took many centuries until Coulomb developed his own theory, and German priest von Klein discovered that the bank is able to store energy. By that time, Van de Graaff generator created the first, all knew what the difference direct current from the AC.
History of alternating and direct electric current
Long since, for example, people have seen that the tourmaline crystal attracts the ashes. By the way, the properties of piezoelectricity was first described by the example of tourmaline.
Comparing the current type
In the early 19th century, it was shown that the heated crystal becomes electrically charged. Due to the strain formed two poles:
- South (analogical).
- Northern (antilogichesky).
And if after the heating temperature remains constant, electricity disappears. Then the appearance of poles already noted upon cooling. It turns out that the tourmaline crystal temperature change produces electricity. Further investigation showed that the capacity of the size depends on:
- Crystal cross-section (cut across the poles).
- Temperature difference.
Other factors influence the amount of charge does not provide. This phenomenon has been called the pyroelectric effect. Dielectric tourmaline slowly charged from a current flowing inside. A charge remained on site (specific surface areas) due to the insulating properties. Until you close the pole conductor tourmaline crystal will continue to accumulate charge as the temperature changes. The line that unites the poles, called the pyroelectric axis.
Piezoelectricity publicly known Curie pair based tourmaline in 1880 year. Realize that changing the dimensions of the crystal will be generated charges remain only come up procedure for the experiment. Curie used to do static pressure normal weight. The experiment is conducted on the insulating surface. For example, a weight of 1 kg causes a tourmaline crystal an electric charge within five hundredths static units.
As there is an electric current
Curiously, the coherent theory of the described phenomenon does not exist yet. It is important to specify that in nature there are charges obtained by various methods. During thunderstorms it occurs at the expense of air masses of friction, moisture and other molecular events. Earth is negatively charged, current flows continuously upward through the atmosphere. Current is called the movement of charge carriers due to some reasons. For example, the potential difference - difference in level of carriers between two points in space.
Comparable to the pressure of the water. When the obstacle is removed, the flow of rush toward lower pressure. Now we take the analogy of tourmaline crystals. Assume there charges on its ends. More need to call the movement, for example, copper wire vein. Uniting the pole, and the electric current will flow. Movement of vehicles will continue until the capacity is on par. In this case, the crystal is discharged.
About variability or constancy of the current can not be said in the course of this during the process. AC and DC are physical ideals, and are used because of the relative ease of production of mathematical models and control them using the technological equipment.
- By this is meant a constant current when carriers flow in a single direction. Number of through-section unequally medium. More broadly constant (rectified) is called the current motion of the charge carriers in the one direction. But the basic concept in physics requires strict conditions. The current is formed is a constant number of carriers moving in the general direction. Moreover, these positive carriers (which is contrary to the practice, where the electrons are for the most part are considered as such).
The principle of the AC
- AC is called not just the one where the carriers move alternately in different directions and do it to the beat. Half period of the wave travels to the left, and the second to the right, so to speak. The carrier density changes in a sinusoidal law. Actually, this is a graph showing the behavior of the process. At the points of zero crossing there is no current. The network is 100 times per second. Consequently, half of the period falls on the carrier motion in the positive direction, and the second - in the negative. Total full cycles per second 50 is formed, which corresponds to a mains frequency of 50 Hz.
Electric current in reality
In practice, current form (charge density dependence on time) is not sinusoidal. For various reasons of the graph is distorted. This, for example, occurs at startup and shutdown of equipment because of the induced noise of various natures. Shape of AC and DC distorted. And long it has been established that it is harmful to the equipment. To combat the scourge of such required methods and mathematics invented spectral analysis.
Fluctuation of any form may be written as the sum of different specific gravity of simple sine waves of different frequencies. It turns out that both components of the mass moving through the circuit, giving a total current. And not necessarily all the components move together with the main mass. Represent like elements ants group, each drags in its side, and the net effect causes the load to move in only one. We mention that, in addition coefficient (amplitude) of each component has a phase (direction) and is referred to as harmonics.
Cascades equipment arranged to useful frequency (preferably 50 Hz) held inside the device, and others took the ground. Set a sign for solving the difficulties mentioned at the outset. Any fluctuation is represented as a set of useful and harmful signals on this basis, equipment design relies properly. For example, in the described working principle, all receivers: current selectively passes desired frequency. So manage to cut the noise, and the wave is transmitted with minimal distortion over long distances.
Examples of the use of AC and DC
Approximately constant current is considered to be a car battery discharge. Voltage is gradually falls, and therefore even when the same load effect varies chronometrically. In general, it happens smoothly. Current flows in one direction and exhibits an approximately constant density. Similarly, work:
- Cell Phone Battery.
- The battery of any type.
- Battery power laptops.
In nature, the constant current sources (generators), with the exception of Mother Earth, no. Man is much easier to create rotors are rotating with the particular frequency, create conditions for forming coils in the stator of the alternating electric current. Then industrial frequency of 50 Hz passes through the wire through the station and is fed to the consumer.
DC power adapter is permissible to consider. This device, operating on alternating DC conversion. Let's say the cell phone is + 5V, and the mobile radios is characterized by a large spread. DC apparatus can function solely of the nominal value for which is designed. Otherwise, any operation is disturbed, or - for large deviations - possible complete failure.
This applies to both AC and DC. Now it's time to say that in the industry of DC to AC conversion and vice versa are not practiced. motors powered by three phases reasons of economy. Each considered alternating current frequency of 50 Hz. We mentioned above, that any harmonic phase is present. In this case, the phase is 120 degrees. A circle is formed by the 360 degrees. It turns out that the three phases are equidistant from each other. If such a scenario generators HPP easier to produce the energy that comes into the house intact. But the apartment comes a single phase AC.
Therefore, home appliances the internal mechanics are very different from the industry. AC parameters is important to recognize. In any country, they are standardized and well maintained. The parameters AC include:
- The effective value of the voltage - in the usual causes permanent conductor of identical rating. The current amplitude value is lower in the root of two times or close to said. Requirements for RF up 220-230 plus or minus 10% of the nominal value.
- To the AC frequency are increased stringent requirements. Limit deviation of 50 Hz is measured in tenths of a percent. Because the stabilization of the movement of the shaft at the HPP is given so much attention. On the speed of rotation depends on the parameter.
- Non-linear distortions are considered a separate topic. many requirements are not easily discernible. Especially strictly normalized harmonic of the fundamental frequency, for example: 100, 150, 200, 250 Hz.
These are the requirements and DC parameters. Assume known car batteries actually include the arsenal is not 12, and 14 V. As the discharge voltage falls. If the battery voltage of 11.9 recorded in the bank is considered to be a failed. We suggest to read the instructions carefully. Supplement: in some notebooks, there is a careful charge the battery power consumption. In this case, the level of support in the framework of two-thirds of the total. It is believed that if the battery will last longer.
Thus, the requirements are intended to maintain a long and proper operation of the equipment. AC and DC parameters are considered to be a factor in determining the reliability and performance of the system.