Electrotechnics: Basics

Electric field

Action at a distance

The concept of interaction between electric charges seen in Coulomb's law, which explains how the interaction of charges. One sign of the charges repel and opposite signs - attract. Coulomb's law is valid for two point charges when there are no other charges near or their value is negligible, that is, as if there are only two operating point charge. If the charges are in motion are not the point, or the charges are in the electric field of the other charges, then it is impossible to apply the formula of Coulomb's law.

The electric force of interaction between charges is described as a non-contact action, and that is to say there is a long-range action, that is action at a distance. In order to describe a long-range convenient to introduce the concept of the electric field and use it to explain the action at a distance.

The concept of an electric field can be expressed in mathematical language in mathematical expressions and terms.

Electric forces are noncontact

The concept of power - a concept (idea) of force in physics, as defined in Newton's three laws. There are two categories of forces: contact and non-contact forces. Gravitational and electric power are non-contact and talk about them as a long-range forces.

Gravitational forces - a long-range forces, they act between two objects, even if they are located at some distance from each other. Car freely sliding down a hill is an example of long-range forces, the Earth attracts another physical body - the car. If you run a shell of artillery, he will move on a parabolic trajectory. During the flight, the projectile he could not in contact with the Earth, and even with its surface, indicating no contact between them. Earth and flying projectile-contact action of gravitational forces. Similarly, such a long-range interaction, and electric charges. Such interaction can be conveniently described using a mathematical representation of the field (electric, gravity).

The concept of the electric field

Provide real field area, for example, one hectare. Let it be sown with wheat. Let's say you wanted to explore where in the space of this field is every grain of wheat and what it has mass. To do this, you will need to take a sheet of paper and draw an area on the scale of the field, first apply the coordinate axes X and the Y. Thus you get a grid-like table, where each cell has its own address as the value of X and Y. Suppose that You managed to find each grain in this field and weigh it, and the result is written in the proper place of this cell. As a result of a full investigation of the real you get a wheat field on a sheet of paper his abstract mathematical representation of the values ​​of the mass of each seed. Just as you can at each location to explore the field of the real temperature, humidity and other physical parameters, and the results also add to the list table. This is an abstract representation of a mathematical field.

There are different physical values ​​and characteristics, which can be divided into two types. It is scalar, that is, without the direction of quantities such as temperature, humidity, mass, density and so on. N., And the vector physical quantities, which, unlike the scalar are characterized not only by the size (number), but the direction. Such a physical quantity like - the force is a vector quantity, meaning it is not only the size (as well as scalar), but also the direction. How to take into account the direction? What is it measured? Temperature, humidity and pressure have a scale in the form of a line (a coordinate axis). This method of measuring scalar values. For vector quantities in the plane, a two coordinate axes and in the space the three coordinate axes is required. In order to determine and measure the direction vector quantities using a vector angle of rotation about the origin. To write a vector is most convenient to use polar coordinates, but it can do the usual Cartesian coordinates.

In the above example with wheat field, when we measured the mass of grains was established mathematical notation scalar value - the mass. This entry can be called a scalar field of mathematics. To describe this way the electric forces acting in the space on the far distance, i.e. without contact, it is necessary to use the vector mathematical notation. This vector notation just will be what is called an electric field. The vector field is different from the scalar greater complexity and deeper understanding, as is necessary to consider the direction of action of physical forces, in addition to their value (scalar).

It is important to remember that the recording sheet of paper in the form of representation of the field lines of force is merely a recording and in reality no such field lines in the space does not exist. For each entry, the image field, is original, that is, the real action of forces in space, or the potential or the actual action. One can say that the recording of the electric field in the form of lines and numbers, colors, and so on. N. - This picture only test space where the springs acting forces are electric charges. This "picture" can not be considered a special kind of matter, but it can be argued that the entire space is filled with fields, sources of which are long-range forces. The source of power is primary, and mathematical notation of the vector or scalar field is secondary. The source of power is real, and the record just a "picture" of the original image.

The image electric field

In order to record information represented as the forces of electric charges using the mathematical vector field, which is depicted in the space in the form of power lines of two types. One kind is the equipotential lines, that is formed by equal values ​​of potential (voltage), and the other type is called the power lines. These field lines intersect the equipotential and scales are the value of forces in the points in space. To build a picture of the electric field is used to compute the value of the electric field. The voltage value is the base, in order to describe the interaction of charges through the presentation of the electric field.

Electric field lines

Date: 01.28.2016

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© Valentin Grigoryev

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