An electric field is called matter, which ensures the interaction of electric charges in it. It can be generated by both an electric charge and a changing magnetic flux. In the first case, it is called electrostatic, in the second - vortex. Without this field, electric current cannot arise, but in order to know how it arises, one should familiarize oneself with the basic characteristics of the electric field.
Content
- The nature of the phenomenon
-
Main characteristics
- Field strength
- Potentials and their difference
- Electric induction
- Static and vortex field
The nature of the phenomenon
It is impossible to see the electric field with the eyes: it can be detected by its action on charged bodies. In this case, such an effect does not require direct contact of the potential carriers, but has a force nature. Thus, electrified hair will be drawn towards other objects.
Observing electric fields shows that they work in a similar way to gravitational ones. This is described by Coulomb's law, which in general looks like this:
F = q₁ q₂ / 4 π ε ε₀ r ²,
where q₁ and q₂ are the values of the charges in coulombs, ε is the dielectric constant of the medium, ε₀ is the electric constant, equal to 8.854 * 10⁻¹² F / m, r is the distance between charges in meters, and F is the force with which the charges interact, in newtons.
Thus, the farther from the center, the less the effect of the field will be felt.
You can display a field graphically in the form of lines of force. Their location will depend on the geometry of the media. There are two types of fields:
- Homogeneous when the lines of force are parallel to each other. The ideal case is infinite parallel charged plates.
- Inhomogeneous, a special case of which is the field around a point or spherical charge; its lines of force diverge radially from the center if it is positive, and to the center if it is negative.
The lines of force of the electric field induced by the electric charge are not closed. They are closed only in the vortex field, which is formed around the changing magnetic flux.
These are the basic properties of an electric field. To get acquainted with its characteristics, it is worth considering the simplest option - electrostatic, which is formed by constant and stationary charges. For convenience, they will be point-like so that their contours do not complicate the calculations. The test charge, which will also appear in the future, will also be point-like and infinitely small.
Main characteristics
They can be described using mathematical patterns, and some can be expressed graphically. The latter characteristics are vector, that is, they have a direction. This is important, since in solving practical problems it is often necessary to operate not with the magnitude of the magnitude, but with the projection of the vector onto some chosen axis.
The main parameters of the field are:
- tension;
- potential;
- induction.
Field strength
This is the strength characteristic of the electric field. The quantity is vector, and it characterizes the force with which the field acts on the charge at a particular point. Mathematically, this is expressed as follows:
Ē = F̄ / q.
If we substitute the formula for Coulomb's law here, we get:
Ē = q₀ / 4 π ε ε₀ r ².
Thus, at each point of the field, its strength is different, and it depends on the charge that it creates, the conditions of the environment and the value inversely proportional to the square of the distance to the point.
If the field is created by two charges, then the resulting strength is calculated graphically - by adding the strength vectors from each individual source. This method is called the principle of superposition.
Potentials and their difference
An electric field is capable of doing work. If the test charge is moved in the field, then the work done by email. field, will depend on the initial and final distance from the test charge to the center of the email. fields. This can be compared to a person who is about to jump from a roof. While he is at the height of the tenth floor, his potential energy will be equal to:
W = -GMm / Rr.
Or if we take into account the proportionality of land and man:
W = mgh.
Until a person has jumped, he has potential energy. When it finally falls, the gravitational field will do work, numerically equal to the above value. This does not take into account horizontal movement - this work was done by the deceased himself.
An electric field works in a similar way. The test charge q₁, placed in it, has potential energy:
W = q₁ q₀ / 4 π ε ε₀ r.
When moving to another point, when the distance r is different, the field will perform work equal to:
A = W₁ - W₂ = q₁ q₀ / 4 π ε ε₀ r₁ - q₁ q₀ / 4 π ε ε₀ r₂.
If we select a parameter from both terms that refers directly to the field, and not to the test charge, it will look like this:
φ₁ = q₀ / 4 π ε ε₀ r₁; φ₂ = q₀ / 4 π ε ε₀ r₂.
And this φ is called the field potential at a point. Based on all the formulas written above, you can express this value as follows:
φ ₁ = W₁ / q₁; φ₂ = W₂ / q₁.
Thus, the work that the field will do will be expressed as follows:
A = W₁ - W₂ = φ₁ q₁ - φ₂ q₁ = q₁ (φ₁ - φ₂).
The expression in parentheses will be called the potential difference, or voltage. It shows what kind of work the field will do to move the test charge.
A / q = (φ₁ - φ₂).
The unit of this value, J / Kl, was named Volt, in honor of the scientist Alessandro Volta. The dimension of other quantities in electrostatics and electrodynamics is measured from this unit. For example, field strength is measured in V / m.
Electric induction
This value characterizes the electric field, as they say, in its pure form. In reality, we are dealing with a field in various media with a certain dielectric constant. Despite the fact that for most substances this is a tabular value, in some cases it is unstable, and its dependence on environmental parameters (temperature, humidity, etc.) ) is nonlinear.
This phenomenon is typical for Rochelle salt, barium titanate, lithium niobate, and a number of others.
Electrical induction is measured in C / m2, and its value is expressed by the formula:
D = ε ε₀ E.
This is also a vector quantity, the direction of which coincides with the direction of tension.
Static and vortex field
As mentioned at the beginning of this article, an electric field can occur around an alternating magnetic field. It even creates a current, which can be achieved in two ways:
- a change in the intensity of the magnetic field passing through the contour of the conductor in it;
- by changing the position of the conductor itself.
In this case, the conductor does not have to be closed at all - the current will still flow in it.
To illustrate the differences between static and vortex fields, a table can be drawn up.
| Parameter | Electrostatic | Vortex |
| field line shape | open | closed |
| what is created | stationary charge | variable magnetic flux |
| source of tension | charge | absent |
| closed loop motion work | zero | creates EMF of induction |
This is not to say that the first and second fields are not connected in any way. This is not true. In reality, the following pattern works: a stationary charge creates an electrostatic field that moves the charge in the conductor; a moving charge generates a constant magnetic field. If the charge moves with a variable speed and direction, then the magnetic field becomes variable and creates a secondary electric one. Thus, the electric field and its characteristics affect the possibility of the occurrence of a magnetic field and its parameters.
