An electric field arises around a charge or charged body in space. In this field, any charge is affected by the electrostatic Coulomb force. A field is a form of matter that transmits force interactions between macroscopic bodies or particles that make up the substance. In an electrostatic field, the force interaction of charged bodies occurs. An electrostatic field is a stationary electric field and is a special case of an electric field created by stationary charges.
The electric field is characterized at each point in space by two characteristics: power - the vector of electrical intensity and energy - potential, which is scalar quantity. The strength of a given point of the electric field is called the vector physical quantity, numerically equal and coinciding in direction with the force acting from the field on a unit positive charge, placed at the field point in question:
An electric field line is a line whose tangents at each point determine the directions of the intensity vectors of the corresponding points of the electric field. The number of field lines passing through a unit area normal to these lines is numerically equal to the magnitude of the electric field strength vector at the center of this area. Tension lines electrostatic field begin on a positive charge and go to infinity for the field created by this charge. For the field created by a negative charge, the lines of force come from infinity to the charge.
The electrostatic field potential at a given point is a scalar quantity numerically equal to potential energy unit positive charge placed this point fields:
The work that is done by the forces of the electrostatic field when moving a point electric charge, is equal to the product of this charge and the potential difference between the starting and ending points of the path:
where and are the potentials of the initial and end points fields when moving a charge.
The tension is related to the potential of the electrostatic field by the relation:
The potential gradient indicates the direction of the fastest change in potential when moving in a direction perpendicular to a surface of equal potential.
The field strength is numerically equal to the change in potential per unit length , measured in the direction perpendicular to the surface of equal potential, and directed in the direction of its decrease (minus sign):
Geometric place points of the electric field whose potentials are the same is called an equipotential surface or surface of equal potential. The intensity vector of each point of the electric field is normal to the equipotential surface drawn through this point. In Fig. 1 graphically depicts the electric field formed by a positive point charge and a negatively charged plane R.
Solid lines are equipotential surfaces with potentials , , etc., dotted lines are field lines, their direction is shown by an arrow.
As is known, characteristic feature conductors is that they always have large number mobile charge carriers, i.e. free electrons or ions.
Inside a conductor, these charge carriers, generally speaking, move chaotically. However, if there is an electric field in the conductor, then the chaotic movement of the carriers is superimposed by their ordered movement in the direction of action electrical forces. This directed movement of mobile charge carriers in a conductor under the influence of a field always occurs in such a way that the field inside the conductor is weakened. Since the number of mobile charge carriers in a conductor is large (the metal contains about free electrons), their movement under the influence of the field occurs until the field inside the conductor disappears completely. Let's find out in more detail how this happens.
Let a metal conductor, consisting of two parts tightly pressed to each other, be placed in an external electric field E (Fig. 15.13). On free electrons In this conductor, field forces act to the left, i.e., opposite to the field strength vector. (Explain why.) As a result of the displacement of electrons under the influence of these forces, an excess of positive charges appears at the right end of the conductor, and an excess of electrons at the left end. Therefore, an internal field (field of displaced charges) arises between the ends of the conductor, which in Fig. 15.13 is shown with dotted lines. Inside
conductor, this field is directed towards the external one and each free electron remaining inside the conductor acts with a force directed to the right.
Strength first more power and their resultant is directed to the left. Therefore, the electrons inside the conductor continue to shift to the left, and the internal field gradually increases. When quite a lot of free electrons accumulate at the left end of the conductor (they still make up an insignificant share from them total number), the force will be equal to the force and their resultant will be equal to zero. After this, the free electrons remaining inside the conductor will move only chaotically. This means that the field strength inside the conductor is zero, i.e., that the field inside the conductor has disappeared.
So, when a conductor enters an electric field, it becomes electrified so that a positive charge appears at one end, and a negative charge of the same magnitude appears at the other. This electrification is called electrostatic induction or electrification by influence. Note that in this case only the conductor’s own charges are redistributed. Therefore, if such a conductor is removed from the field, its positive and negative charges will again be evenly distributed throughout the entire volume of the conductor and all its parts will become electrically neutral.
It is easy to verify that at the opposite ends of a conductor electrified by influence, there are indeed equal amounts of charges of opposite sign. Let's divide this conductor into two parts (Fig. 15.13) and then remove them from the field. By connecting each part of the conductor to a separate electroscope, we will make sure that they are charged. (Think about how you can show that these charges have opposite signs.) If we again connect the two parts so that they form one conductor, we will find that the charges are neutralized. This means that before the connection, the charges on both parts of the conductor were equal in magnitude and opposite in sign.
The time during which the conductor is electrified by the influence is so short that the balance of charges on the conductor occurs almost instantly. In this case, the tension, and therefore the potential difference inside the conductor, becomes everywhere equal to zero. Then for any two points inside the conductor the relation is true
Consequently, when the charges on the conductor are in equilibrium, the potential of all its points is the same. This also applies to a conductor electrified by contact with a charged body. Let's take a conducting ball and place a charge at point M on its surface (Fig. 15.14). Then in the explorer on short time a field arises, and at point M an excess charge occurs. Under the influence of the forces of this field
the charge is evenly distributed over the entire surface of the ball, which leads to the disappearance of the field inside the conductor.
So, regardless of how the conductor is electrified, when the charges are in equilibrium, there is no field inside the conductor, and the potential of all points of the conductor is the same (both inside and on the surface of the conductor). At the same time, the field outside the electrified conductor, of course, exists, and its intensity lines are normal (perpendicular) to the surface of the conductor. This can be seen from the following reasoning. If the tension line were somewhere inclined to the surface of the conductor (Fig. 15.15), then the force acting on the charge at this point on the surface could be decomposed into components. Then, under the influence of a force directed along the surface, the charges would move along the surface of the conductor, which There should be no charge equilibrium. Consequently, when the charges on the conductor are in equilibrium, its surface is an equipotential surface.
If there is no field inside a charged conductor, then bulk density charges in it (the amount of electricity per unit volume) must be zero everywhere.
Indeed, if there was a charge in any small volume of a conductor, then an electric field would exist around this volume.
In field theory it has been proven that at equilibrium, all the excess charge of an electrified conductor is located on its surface. This means that all inner part This conductor can be removed and nothing will change in the arrangement of charges on its surface. For example, if two solitary metal balls of equal size, one of which is solid and the other is hollow, are equally electrified, then the fields around the balls will be the same. M. Faraday was the first to prove this experimentally.
So, if a hollow conductor is placed in an electric field or electrified by contact with a charged body, then
When the charges are in equilibrium, the field inside the cavity will not exist. Electrostatic protection is based on this. If any device is placed in a metal case, then external electric fields will not penetrate inside the case, i.e., the operation and readings of such a device will not depend on the presence and changes of external electric fields.
Let us now find out how the charges are arranged along outer surface conductor. Let's take a metal mesh on two insulating handles, to which paper leaves are glued (Fig. 15.16). If you charge the mesh and then stretch it (Fig. 15.16, a), the leaves on both sides of the mesh will separate. If you bend the mesh into a ring, then only the leaves with outside grids (Fig. 15.16, b). By giving the mesh a different bend, you can make sure that the charges are located only on the convex side of the surface, and in those places where the surface is more curved ( smaller radius curvature), more charges accumulate.
So, the charge is distributed evenly only over the surface of a spherical conductor. At free form conductor surface density charges a, and therefore the field strength near the surface of the conductor is greater where the curvature of the surface is greater. The charge density is especially high on the protrusions and on the tips of the conductor (Fig. 15.17). This can be verified by touching various points of the electrified conductor with a probe and then touching the electroscope. An electrified conductor that has points or is equipped with a point quickly loses its charge. Therefore, the conductor on which the charge must be stored for a long time, should not have any points.
(Think about why the rod of an electroscope ends in a ball.)
What allows us to say that there is an electric field around a charged body?
- The presence of electromagnetic voltage and vortex fields.
- the effect of an electric field on a charge.
simple experience:
1. take a wooden stick and tie a sleeve made from a shiny chocolate wrapper to it with a silk thread.
2. rubbing the handle on hair or wool
3. bring the handle to the sleeve - the sleeve will deviate
this allows us to assert that around a charged body (in in this case pens, there is an electric field))) - someone help me solve this problem
http://otvet.mail.ru/question/94520561 - everything is in the textbook)
- Link (electrono.ru Electric field strength, electric...)
- In the space around an electrically charged body there is an electric field, which is one of the types of matter. The electric field has a reserve electrical energy, which manifests itself in the form of electrical forces acting on charged bodies in the field.
The electric field is conventionally depicted in the form of electric lines of force, which show the directions of action of the electric forces created by the electric field.
Electrical power lines diverge into different sides from positively charged bodies and converge at bodies with a negative charge. The field created by two flat oppositely charged parallel plates is called uniform.
The electric field can be made visible by placing gypsum particles suspended in liquid oil into it: they rotate along the field, positioning themselves along its power lines. A uniform field is an electric field in which the intensity is the same in magnitude and direction at all points in space.Wikipedia: For quantification electric field is introduced power characteristic- electric field strength - vector physical quantity, equal to the ratio the force with which the field acts on a positive test charge placed at a given point in space, to the magnitude of this charge. The direction of the tension vector coincides at each point in space with the direction of the force acting on the positive test charge.
The field between two oppositely charged flat metal plates is approximately uniform. In a uniform electric field, the tension lines are directed parallel to each other. - Recharge yourself and pour some fluff out of your pillow. Everything will be very clear.
- If you bring another electrically charged object to the first one, it is also electric. charged object, then you can see their interaction, which proves the existence of an electric field.
- Allows you to calculate the laws of physics
- Electric field - special shape matter that exists around bodies or particles with an electric charge, as well as in free form in electromagnetic waves Oh. The electric field is directly invisible, but can be observed by its action and with the help of instruments. The main effect of the electric field is the acceleration of bodies or particles with an electric charge.
The electric field can be considered as mathematical model, describing the value of the electric field strength at a given point in space. Douglas Giancoli wrote: “It should be emphasized that the field is not some kind of substance; or rather, it is an extremely useful concept... The question of “reality” and the existence of the electric field is actually a philosophical, rather even metaphysical question. In physics, the concept of field has proven to be extremely useful - it is one of the greatest achievements human mind."
The electric field is one of the components of a single electromagnetic field and the manifestation of electromagnetic interaction.
Physical properties of the electric field
At present, science has not yet reached an understanding physical entity fields such as electric, magnetic and gravitational, as well as their interactions with each other. The results have just been described so far. mechanical impact on charged bodies, and there is also a theory of electromagnetic waves, described by Maxwell's Equations.Field effect - The field effect is that when an electric field is applied to the surface of an electrically conducting medium, the concentration in its near-surface layer changes free media charge. This effect underlies the operation of field-effect transistors.
The main effect of the electric field is the force effect on stationary (relative to the observer) electrically charged bodies or particles. If a charged body is fixed in space, then it does not accelerate under the influence of force. The magnetic field (the second component of the Lorentz force) also exerts a force on moving charges.
Observing the electric field in everyday life
In order to create an electric field, it is necessary to create an electric charge. Rub some dielectric on wool or something similar, such as a plastic pen on your own hair. A charge will be created on the handle, and an electric field will be created around it. A charged pen will attract small pieces of paper. If you rub a larger object, such as a rubber band, on wool, then in the dark you will be able to see small sparks resulting from electrical discharges.An electric field often occurs near the television screen when the television receiver is turned on or off. This field can be felt by its effect on the hairs on the hands or face.
The electric field is one of the theoretical concepts, explaining the phenomena of interaction between charged bodies. The substance cannot be touched, but its existence can be proven, which was done in hundreds of natural experiments.
Interaction of charged bodies
We are accustomed to considering outdated theories a utopia, yet men of science are not at all stupid. Today Franklin’s doctrine of electric fluid sounds funny; the prominent physicist Apinus dedicated an entire treatise. Coulomb's law was discovered experimentally based on torsion scales, similar methods were used by Georg Ohm when deducing the known. But what lies behind all this?
We must admit that the electric field is simply another theory, not inferior to the Franklin fluid. Today two facts are known about the substance:
The stated facts laid the basis for the modern understanding of interactions in nature and act as a support for the theory of short-range interaction. In addition to this, scientists have put forward other assumptions about the essence of the observed phenomenon. The theory of short-range action implies the instantaneous distribution of forces without the participation of the ether. Since phenomena are more difficult to sense than an electric field, many philosophers have dubbed such views idealistic. In our country they were successfully criticized Soviet power, since, as you know, the Bolsheviks did not like God, they pecked at every opportunity the idea of the existence of something “depending on our ideas and actions” (while studying Juna’s superpowers).
Franklin explained the positive and negative charges of bodies by excess and insufficiency of electrical fluid.
Electric field characteristics
The electric field is described by a vector quantity - intensity. An arrow whose direction coincides with the force acting at a point on a unit positive charge, the length of which is proportional to the magnitude of the force. Physicists find it convenient to use potential. The quantity is scalar; it is easier to imagine it using the example of temperature: at each point in space there is a certain value. Electric potential refers to the work done to move a unit charge from a point of zero potential to a given point.
A field described in the above manner is called irrotational. Sometimes called potential. The electric field potential function is continuous and varies smoothly over the extent of space. As a result, we select points of equal potential that fold the surfaces. For a unit charge sphere: further object, weaker field(Coulomb's law). Surfaces are called equipotential.
To understand Maxwell's equations, understand several characteristics vector field:
- Gradient electric potential called a vector, the direction coincides with the fastest growth of the field parameter. The faster the value changes, the greater the value. The gradient is directed from smaller value potential for more:
- The gradient is perpendicular to the equipotential surface.
- The greater the gradient, the closer the location of equipotential surfaces that differ from each other by specified value electric field potential.
- The potential gradient, taken with the opposite sign, is the electric field strength.
Electric potential. Gradient "climbing uphill"
- Divergence is a scalar quantity calculated for the electric field strength vector. It is analogous to a gradient (for vectors), shows the rate of change of a value. The need to introduce an additional characteristic: the vector field has no gradient. Therefore, the description requires a certain analogue - divergence. Parameter in mathematical notation similar to a gradient, denoted Greek letter nabla, used for vector quantities.
- The rotor of the vector field is called a vortex. Physically, the value is zero when the parameter changes uniformly. If the rotor is non-zero, closed line bends occur. Potential fields point charges by definition, there is no vortex. The lines of tension in this case are not necessarily straight. They simply change smoothly, without forming vortices. A field with a non-zero rotor is often called solenoidal. The synonym is often used - vortex.
- The total flux of the vector is represented by the surface integral of the product of the electric field strength and the elementary area. The limit of magnitude when the body's capacitance tends to zero represents the divergence of the field. The concept of limit is studied in senior classes high school, the student can get some idea about the subject of discussion.
Maxwell's equations describe a time-varying electric field and show that in such cases a wave arises. It is generally accepted that one of the formulas indicates the absence of isolated magnetic charges(poles). Sometimes in the literature we come across a special operator – the Laplacian. Denoted as the square of the nabla, calculated for vector quantities, represented by the divergence of the field gradient.
Using these quantities, mathematicians and physicists calculate electric and magnetic fields. For example, it has been proven: only an irrotational field (point charges) can have a scalar potential. Other axioms have been invented. The vortex field of the rotor is devoid of divergence.
We can easily use such axioms as the basis for describing the processes occurring in real existing devices. Anti-gravity, perpetual motion machine would be a good help to the economy. If no one has succeeded in putting Einstein’s theory into practice, Nikola Tesla’s achievements are being studied by enthusiasts. There is no rotor or divergence.
A Brief History of the Development of the Electric Field
The formulation of the theory was followed by numerous works on the application of electric and electromagnetic fields in practice, the most famous of which in Russia is considered to be Popov’s experience in transmitting information through the air. A number of questions arose. Maxwell's harmonious theory is powerless to explain the phenomena observed during the passage of electromagnetic waves through ionized media. Planck hypothesized that radiant energy is emitted in measured portions, later called quanta. Diffraction of individual electrons, kindly demonstrated on YouTube in English, was discovered in 1949 Soviet physicists. The particle simultaneously exhibited wave properties.
This tells us: modern performance about the electric field constant and variable are far from perfect. Many people know Einstein, but are powerless to explain what the physicist discovered. The 1915 theory of relativity links electrical, magnetic field and gravity. True, no formulas were presented in the form of a law. Today it is known: there are particles that move faster than the propagation of light. Another stone in the garden.
Unit systems were constantly changing. The initially introduced GHS, based on the work of Gauss, is not convenient. The first letters indicate the basic units: centimeter, gram, second. Electromagnetic quantities added to the GHS in 1874 by Maxwell and Thomson. The USSR began using the ISS (meter, kilogram, second) in 1948. The introduction of the SI system (GOST 9867) in the 60s of the 20th century put an end to the battles, where the electric field strength is measured in V/m.
Using an electric field
Electric charge accumulates in capacitors. Consequently, a field is formed between the plates. Since the capacitance directly depends on the magnitude of the voltage vector, in order to increase the parameter, the space is filled with a dielectric.
Indirectly, electric fields are used by picture tubes and Chizhevsky chandeliers; the grid potential controls the movement of electron tube beams. Despite the lack of a coherent theory, electric field effects underlie many images.
