The electric potential is a scalar physical quantity characterizing the field strength. The parameter also expresses the electrical voltage.
Physical meaning of the electric field
Scientists have long puzzled over the substances of the electric and magnetic fields, but so far this is a mystery to them, like gravity.existence is not contested, but the essence is unclear. People didn’t know the secret of electricity long before our era, and they didn’t strive to explore.
Major achievements in the study of electricity would have happened at least 20 years earlier than in reality. Before Oersted, Giovanni Domenico Romanozi in 1802 noted the influence of a wire with a current on a magnetic needle. This is confirmed by official publications data, and the actual event may have happened earlier. The merit of Oersted only in the focus of public attention on the observed fact.
Similar examples of darkness. Sometimes scientists, regardless of each other, made discoveries, inventions. There were cases when the husband of science thought that his inventions were not new. Then he was surprised when it turned out that authorship now belongs to a stranger, although his own discovery happened earlier in time. Silence guaranteed the transition of the share of fame to the event described. This happened in the XIX century - scientists constantly cooperated, discussed something, sometimes it was hard to find ends. For example, Faraday blamed for the plagiarism of the design of the first human engine, and Wikipedia attributed to him the authorship of the inductor invented by Laplace, for which Michael did not claim. However, when it comes to the matter of the fields, scientists keep a united silence. The only exception was Nikola Tesla, who asserted that everything in the Universe consists of harmonic oscillations.
So, scientists do not know anything about the field, and the electric potential is a characteristic of the field. Nobody saw the substance, they were not able to register for a long time and are hardly present today! Do not believe it - try to draw in the imagination of an electromagnetic wave:
- It is known that the oscillation is a superposition of electric and magnetic fields, changing in time.
- The vector of magnetic intensity is perpendicular to the electric vector, connected through a medium constant( a certain physical quantity).
- In appearance, these are two perpendicular waves. .. stop! What is a wave?
This is what modern physics looks like. No one knows exactly what the field, the oscillation, the wave looks like, how to draw it. It is clear only: pictures from the textbook poorly describe what is happening. The matter is aggravated by the inability of a person to see and feel electromagnetic radiation. Oscillation does not look sinusoidal, is considered for one point, line, front, etc. It is rather a compaction and stretching of the ether, something resembling a three-dimensional indescribable figure.
A long introduction shows how unexplored is what is used in everyday life. And sometimes poses a real danger to humans. For example, it is proved that the radiation of the microwave oven gradually "spoils" the food. A person who regularly eats from the microwave runs the risk of getting an extensive list of ailments at his disposal. First of all - blood diseases. Unsafe for people and the network frequency of 50 Hz.
Characteristics of the electric field
The man quickly realized that there was an electric field, already in the 18th century - or earlier - his picture was painted with sawdust. People saw lines emerging from the poles. By analogy, began to try to portray the electric field. For example, Charles Coulomb at the end of the eighteenth century discovered the law of attraction and repulsion of charges. Writing the formula, I realized that the equipotential lines of the interaction force concentrically diverge around a point cluster of electricity, and the trajectories of motion are straight.
This is how the first picture of the electric field appeared. It reminds a picture of how the researchers represented a magnetic one, but with a giant difference: in nature there were charges of both signs. The lines of tension go to infinity( in theory, of course, they will end).And the magnetic charges are not found one by one, their lines are always closed in the visible region of space.
For the rest, there was much in common, for example, charges of the same sign repel each other and attract each other. This is true for magnets and electricity. Hilbert remarked that magnetism is a strong substance that is difficult to screen or destroy, and electricity is easily destroyed by moisture and other substances. He added Coulomb to the barrel, which, following Benjamin Franklin, assigned a negative charge to the electrons. Although it was about the amount of fluid. And the excess electrons should be called positive.
As a result, the field strength lines are arranged in the opposite direction to the correct one. The potential grows not there. .. The main characteristics of the electric field are:
- Tension - shows what force acts on a positive unit charge at a given point from the field.
- Potential - shows what kind of work a field can expend to move a single test positive charge to an infinitely distant point.
- Voltage - the potential difference between two points. Voltage is determined solely on some level.
The most likely origin of terms from the Latin language. The tension was put into use, presumably, by Alessandro Volta, and the potential is called by the name of the field type, which is characterized by a specified value: the work on moving the charge does not depend on the trajectory is equal to the difference of the potentials of the initial and final points. Consequently, on a closed trajectory is zero.
Zero potential and potential field
The electric field is considered potential, which means that the work of moving the charge in it does not depend on the trajectory and is determined solely by the potential. Potential is a universal physical concept, often used. For example, for the gravitational field of the Earth, the origin of which is still inexplicable. It is known that the masses are attracted by the law, reminiscent of that derived by Charles Coulomb.
In an electric field, the globe becomes the starting point. There is no difference as to what to calculate the potential, but people quickly realized that pitch electricity beats, glass bites with electricity, and the ground does not cause harm. Therefore, in full accordance with the logic adopted for zero. This is a plus: the Earth is huge in size, giant currents, static and variable, flow easily onto the planet. It is proved that on the body the charge is trying to distribute mutually at the maximum distance. What corresponds to the surface of the planet. In this scenario, the charge density turns out to be insignificant, much less than on any electrified body.
On Earth, potential with rare exceptions is measured relative to the ground, the value is called electrical voltage. From the context it becomes clear that the voltage is positive and negative. However, not always. On power lines, it is sometimes considered advantageous to use circuits with insulated neutral. Then the potential of any point is not considered relative to the Earth, there is no neutral. This becomes possible in three-phase circuits.
An isolation transformer is installed at the local substation, the secondary neutral of which is grounded in order to supply consumers with a phase voltage of 220 V and not a linear one. Sometimes people naively think that the planet is one, therefore, a neutral is not needed, the current will still flow. But it will flow through the ground, causing considerable economic damage and posing a danger to people by the creation of stepwise tension. Copper conductor zero - called returnable in the first half of the XIX century - has little resistance and is guaranteed not to cause harm.
In circuits with insulated neutral, the potential is not measured relative to the ground level, and the voltage is measured between two points. It is worth mentioning that, according to Ohm’s law, the current flowing through a conductor creates a potential difference. Therefore, it is not possible to undertake an earth loop at an accident. Low resistance can be the cause of the formation of a considerable potential difference here. And a person must remember about the danger of the voltage of touch.
However, circuits with insulated neutral are also used for security purposes. If the voltage is created between two points of the secondary winding of the isolation transformer, the current to the ground through the careless person who takes up the bare wire will not go - the potential difference relative to the ground is less. Consequently, the isolation transformer becomes a measure of protection and is often used in practice.
Potential drop in an external electrical circuit
An external electrical circuit is an area outside the source. In practice, the EMF is produced on the secondary windings of a three-phase transformer of a substation, being considered a source. Starting with the pin, there is an external circuit.
On it, the potential drops from phase to neutral voltage. We are talking about ordinary consumers. When electricity comes to the house, it is invariably a three-phase current system. The neutral is deafly grounded to ensure the desired level of security. Residential building does not guarantee uniform loading of all phases, current will flow through the neutral. If the circuit is used for protection, there is no complete guarantee of security: the current path is able to flow through a person who suddenly takes up the grounding conductor.
Therefore, it is necessary to provide two neutral conductors: working and protective. Through the first, the metal parts of the object are zeroed off, through the second - grounding. And abroad, it is common to divide two branches into two different lines, and in the Russian Federation they are combined in the area of the ground loop. The first is made for reliable protection, the second - for the ability to work in the building of three-phase equipment( suddenly come in handy!).If the industrial installation leaves only the grounding of the case, it will end badly for a loser who has fallen under the electric potential.
Consequently, the western system is good for single-phase equipment. But due to the unification of the system of the Russian Federation more difficult. Imported equipment does not fit well with Russian conditions: the power filters are designed so that the protective and working neutral conductors do not overlap. The reason for the electric potential:
- On the protective conductor is always the potential of the soil - zero.
- At the working, a different value is permissible due to the voltage drop on the wires of the power supply line.
To equalize the difference, the lines at the entrance to the building are combined and lead to the lightning circuit. That for imported equipment does not become an ideal solution, the companies-suppliers of electricity suffer losses. This is the well-known system TN-C-S, used in the Russian Federation. Houses built back in the USSR are gradually being re-equipped.