The electrostatic field is a special type of electro magnetic field... It is created by a set of electric charges, motionless in space in relation to the observer and constant in time. The charge of a body is understood as a scalar quantity, which, as a rule, we will deal with a field created in a homogeneous and isotropic medium, that is, in such, electrical properties, which are the same for all points of the field and do not depend on the direction. An electrostatic homogeneous field has the ability to act isotropically on an electric charge placed in it with a mechanical force directly proportional to the magnitude of this charge. The determination of the electric field is based on its mechanical manifestation. It is described by Coulomb's law.
- Coulomb's law.
Two point charges q 1 and q 2 in a vacuum interact with each other with a force F directly proportional to the product of the charges q 1 and q 2 and inversely proportional to the square of the distance between them R. This force is directed along the line connecting the point charges. Charges of the same name are repelled, and unlike charges are attracted.
Where is the unit vector directed along the line connecting the charges.
Electric constant ( 
)
When using SI, the distance R is measured in meters, the charge - in pendants (C), the force - in newtons.
- Tension electrostatic field.
Any field is characterized by some basic values. The main quantities characterizing the electrostatic field are tensionand potential.
The electric field strength is numerically equal to
the ratio of the force F acting on a charged particle to the charge q and has the direction of the force that acts on a particle with a positive charge. In this way
- this is the strength characteristic of the field, determined on the condition that the charge introduced into a given point did not distort the field that existed before the introduction of this charge. Hence it follows that the force acting on a finite value, the point charge q introduced into the field will be equal to 
, and the tension is numerically equal to the force acting on the charge, equal in magnitude to one. If the field is created by several charges ( 
), then its intensity is equal to the geometric sum of the intensities from each of the charges separately:
, that is, with electric
fields apply the overlay method.
An electrostatic field can be characterized by a combination of lines of force and equipotential lines. A line of force is a line drawn mentally in a field that begins on a positively charged body. It is carried out in such a way that the tangent to it at any point gives the direction of the field strength Ē at this point. A very small positive charge would move along the line of force if it were able to move freely in the field and did not have inertia. Thus, the lines of force have a beginning (on a positively charged body) and an end (on a negatively charged body).
Equipotential (equally potential) surfaces can be drawn in an electrostatic field. An equipotential surface is understood as a set of rest points that have the same potential. Moving on this surface does not change the potential. Equipotential lines and lines of force at any point of rest intersect at right angles. There is a relationship between the strength of the electric field and the potential:
or 
, where for q \u003d 1
The potential of an arbitrary point of the field 1 is defined as the work done by the forces of the field on the transition of a unit positive charge from a given point of the field to a point in the field, the potential of which is zero.
- The flow of the vector through the surface element and the flow of the vector through the surface.
Let in the vector field (for example, in the field of the electric field strength vector Ē) there is some element of the electric field surface, the area of \u200b\u200bwhich is numerically equal on one side.
Let's choose the positive direction of the normal (perpendicular) to the surface element. We put the vector equal area surface element, and its direction coincides with the positive direction of the normal. In the general case, the flux of the vector Ē through an element of the surface is determined by the scalar product 
... If the surface. Through which the flux of the vector is determined, is large, then it cannot be assumed that at all points Ē is the same. In this case, the surface is subdivided into individual elements of small dimensions, and the total flux is equal to the algebraic sum of fluxes through all elements of the surface. The sum of the flows is written as an integral 
.
The S under the integral icon means that the summation is performed over all surface elements. If the surface through which the vector flux is determined is closed, then a circle is placed on the integral sign:
- Polarization.
Polarization is understood as an ordered change in the arrangement of bound charges in the body, caused by an electric field. This is manifested in the fact that negatively bound charges in the body will move towards a higher potential, and positive ones vice versa.
a)
The product is called the electrical of two equal in magnitude and opposite in sign charges, located at a distance from each other (dipole). In a polarized substance, molecules are electrically dipoles. Under the action of an external electric field, the dipoles tend to orient themselves in space in such a way that their electric moment is directed parallel to the vector of the electric field strength. The electric moment of the sum of dipoles in the volume of a substance V, referred to the volume V as V tends to zero, is called polarization (polarization vector).
For most dielectrics t wx: val \u003d "Cambria Math" /\u003e
A vector is equal to the sum of two vectors: vectors 
, which characterizes the field in vacuum, and polarization, which characterizes the ability of the dielectric to polarize at the point under consideration:
As 
then 
Where 
; 
Relative dielectric constant has dimension zero; they show how many times the absolute dielectric constant of a substance () is greater than the electrical constant characterizing the properties of vacuum. In the SI system, [D] \u003d [P] \u003d Cl /
- Gauss's theorem in integrated form.
Gauss's theorem is one of greatest theorems electrostatics.
It complies with Coulomb's law and the superposition principle. The theorem can be formulated and written in three ways.
The flux of the electric displacement vector through any closed surface surrounding a certain volume is equal to the algebraic sum of free charges inside this surface:
From this formula it follows that the vector is such a characteristic of the field, which, other things being equal, does not depend on the dielectric properties of the medium (on the magnitude).
As 
, then Gauss's theorem for a homogeneous and isotropic medium can be written in the following form:
that is, the flux of the electric field strength vector through any closed surface is equal to the sum of free charges inside this surface, divided by the product. It follows from this formula that the vector is a characteristic of the field, which, in contrast to the vector, other things being equal, depends on the dielectric properties of the medium (on the magnitude). The vector flux is determined only by the sum of the charges and does not depend on their location inside the closed surface.
The flow of a vector through any closed surface is created not only by the sum of free charges ( 
), but also by the sum of bound charges ( 
) inside the surface. It is known from the physics course that the flux of the polarization vector through any closed surface is equal to the algebraic sum of bound charges inside this surface taken with the opposite sign:
The first version of Gauss's theorem can be written as follows:
Hence
- application of the Gauss theorem to determine the potential strength in the field of a point charge.
Gauss's theorem in integral form can be used to find the strength or electrical displacement at any point in the field, if a closed surface can be drawn through this point in such a way that all its points will be in the same (symmetric) conditions with respect to the charge inside the closed surface ... As an example of using the Gauss theorem, we find the field strength created by point charges at a point remote at a distance R from the charge. For this purpose, through a given point, draw a spherical surface of radius R from the charge.
The surface element ___ is perpendicular to the surface of the sphere and is directed towards the outer (with respect to the volume inside the surface) surface. In this case, at each point, the sides ___ and ___ coincide in direction. The angle between them is zero.
By Gauss's theorem:
Consequently, the tension created by a point charge q at a distance R from it will be determined as
- Gauss's theorem in differential form.
Gauss's theorem in integral form expresses the relationship between the flow of a vector through a surface bounding a certain volume, and the algebraic sum of the charges inside this volume. However, using the Gauss theorem in integral form, it is impossible to determine how the flux of lines at a given point of the field is related to the density of free charges at the same point of the field. The answer to this question is given by the differential form of Gauss' theorem. Let us divide both sides in the equation of the first way of writing the Gauss theorem in integral form by one and the same scalar quantity - by the volume V located inside the closed surface S.
Let the volume go to zero:
When the volume tends to zero 
also tend to zero, but the ratio of two infinitesimal quantities 
and V is a constant (finite) value. The limit of the ratio of the flow of a vector quantity through a closed surface bounding a certain volume to the volume V is called the vector divergence 
... Often, instead of the term “divergence”, the term “divergence” or “source” of a vector is used. As 
is the volumetric density of free charges, then the Gauss theorem in differential form is written as follows (first notation):
That is, the source of the lines at a given point of the field is determined by the value of the density of free charges at this point. If the bulk charge density at a given point is positive ( 
), then from the infinitely small volume surrounding a given point of the field, the lines of the vector emanate (the source is positive). If at a given point of the field 
, then the lines of the vector enter the infinitesimal volume, inside which the given point is located. And finally, if at any point in the field 
, then at a given point of the field there is neither a source nor a drain of lines, that is, at a given point, the lines of the vector do not begin or end.
If the medium is homogeneous and isotropic, then its 
... Instead of the first form of writing the Gauss theorem, we write in the differential form:
Let's find out the meaning behind the differential sign 
... Hence
This expression is the second notation of the Gauss theorem
The third form of writing the Gauss equation in integral form is described by the expression
The same equation in differential form will be written as
Therefore, the source of the vector ______, in contrast to the source of the vector _____, are not only free, but also bound charges
- Corollary to Gauss's theorem.
Any equipotential surface can be replaced with a thin conductive uncharged layer without changing the electric field outside the layer. The converse is also true: a thin uncharged layer is possible and the field does not change.
Lecture 2.
- The work of the forces of the electric field.
Let's place some charge q in the electric field. Force will act on the charge 
.
Let the charge q from point 1 move to point 2 along the path 1 - 3 - 2. Since the direction of the force acting on the charge at each point of the path may not coincide with the element of the path, the work of moving the charge along the path is determined by the scalar product of the force by path element 
... The work spent on transferring the charge from point 1 to point 2 along the path 1 - 3 - 2 is defined as the sum of elementary work 
... This sum can be written as a linear integral
The charge q can be anything. Let's set it equal to one. By the potential difference (or voltage), it is customary to understand the work expended by the field forces when transferring a unit charge from the starting point 1 to the end point 2:
This definition is an integral feature of the potential field.
If the potential of the end point of path 2 were equal to 0, then the potential of point 1 would be determined as follows (for 
):
that is, the potential of an arbitrary point of the field 1 can be defined as the work done by the forces of the field to transfer a unit charge 9 (positive) from a given point of the field to a point in the field, the potential of which is zero. Usually, in physics courses, a point with zero potential is at infinity. Therefore, the definition of the potential is given as the work performed by the field forces during the transfer of a unit charge from a given point of the field to infinity: 
It is often believed that a point with zero potential is on the surface of the earth (the earth under electrostatic conditions is a conducting body), so it makes no difference where exactly on the surface of the earth or in its thickness this point is located. Thus, the potential of any point in the field depends on which point in the field is given a zero potential, that is, the potential is determined with accuracy to a constant value. However, this is not essential, since it is not the potential of any point in the field that is practically important, but the potential difference and the derivative of the potential along the coordinates.
- The electric field is a potential field.
Let us define an expression for the potential difference in the field of a point charge. For this purpose, we assume that at point m there is a positive point charge that creates a field; and from point 1 to point 2 through the intermediate point 3 a unit positive charge q \u003d 1 moves.
Let's denote the distance from point m to the starting point 1; - distance from point m to end point 2; R is the distance from point m to an arbitrary point 3 on the path 1 - 3 - 2. The direction of the field strength and the direction of the path element at the intermediate point 3 generally do not coincide. Scalar product 
, where dR is the projection of the path element in the direction of the radius connecting point m with point 3.
According to the definition of field strength 
... According to Coulomb's law:
As 
and q \u003d 1, then the modulus of the field strength in the field of a point charge
Substituting the formula for determining the potential difference
instead of the value we get
We draw an important conclusion: the potential difference between the initial and final points of the path (points 1 and 2 in our example) depends only on the position of these points and does not depend on the path along which the movement from the starting point to the final one took place.
If the field is created by a set of point charges, then this conclusion is valid for the field created by each of the point charges separately. And since the superposition principle is valid for an electric field in a homogeneous and ________________ dielectric, the conclusion about the independence of the value of the potential difference __________ from the path along which the movement from point 1 to point 2 took place is also valid for the electric field created by a set of point charges.
If you walk along the closed path 1 - 3 - 2 - 4 - 1, then the starting point of path 1 and the end point of path 2 coincide, and then the left and right sides of the potential difference formula will be equal to 0:
The circle on the integral symbol means that the integral is taken along a closed contour.
An important conclusion follows from the last expression: in an electrostatic field, the linear integral of the electric field strength taken along any closed loop is equal to zero. Physically, this is explained by the fact that when moving along a closed path, a certain work is done by the forces of the field and the same work is done by external forces against the forces of the field. Equality (2.1) is interpreted as follows: the circulation of a vector along any closed path is equal to zero. This relationship expresses the main property of the electrostatic field. The fields for which this kind of relationship is satisfied are called potential. Potential are not only electrostatic, but also gravitational fields (the force of gravity between material bodies)
- Expression of tension in the form of a potential gradient.
The gradient of a scalar function is the rate of change of a scalar function, taken in the direction of its greatest increase. In determining the gradient, two provisions are essential: 1) the direction in which the two nearest points are taken must be such that the rate of potential change is maximum; 2) the direction should be such that the scalar function does not decrease in this direction.
In an electrostatic field, we take two adjacent points at different equipotentials. Let 
... Then, in accordance with the above definition, we will depict the gradient as a vector perpendicular to the equipotential lines and directed from and (in the direction of increasing the potential). Denote by dn the perpendicular distance (along the normal) between equivalent surfaces, and by the vector coinciding with the directions; through is a unit vector in the direction 
, but based on the comparison to determine the potential difference, you can write the expression
where 
increment of potential when going from point 1 to point 2. As 
, then the increment is negative.
Since the vectors and coincide in direction, the scalar product is equal to the product of the modulus by the modulus ( 
). In this way, 
... Hence the field directivity modulus 
... Field strength vector
.
Hence
(4.1)
It follows from the definition of the gradient that
(4.2)
(The gradient vector is always directed in the direction opposite to the vector).
Comparing (4.1) and (4.2), we conclude that
(4.3)
This is a differential equation of the relationship between strength and potential.
Relation (4.3) is interpreted as follows: the intensity at any point of the field is equal to the rate of change of the potential at this point, taken with the opposite sign. A sign (-) means that direction and direction 
are opposite.
It should be noted that the normal in the general case can be located so that it does not coincide with the direction of any coordinate axis, and therefore the potential gradient in the general case can be represented as the sum of three projections along the coordinate axes. For example, in a Cartesian coordinate system:
Where is the rate of change in the direction of the X axis; - numerical value (module) of speed (speed is a vector value); 
- unit unit vectors, respectively, along the X, Y, Z axes of the Cartesian system.
Tension vector 
... In this way,
Two vectors are equal only if their corresponding projections are equal to each other. Hence,
(4.4)
Relation (4.4) should be understood as follows: the projection of the field strength on the X axis is equal to the projection of the rate of change in the potential along the X axis, taken with the opposite.
Lecture 3.
- Hamiltonian differential operator (nabla operator).
To shorten the writing of various operations on scalar and vector quantities, the Hamilton differential operator (nabla operator) is used. The Hamilton differential operator is understood as the sum of partial derivatives along three coordinate axes, multiplied by the corresponding unit vectors (unit vectors). In the Cartesian coordinate system, it is written as:
It combines vector and differentiating properties and can be applied to scalar and vector functions. The one, the action on which, although to perform (differentiation by its coordinates, or, spatial differentiation), is written to the right of the operator nabla.
Let's apply the operator to the potential. For this purpose, we write
If we compare (2.1) with 
, - then 
, and assigning an operator to the left to some scalar function (in this case, to) means taking the gradient from this scalar function.
- Poisson and Lanlass equations.
These equations are the basic differential equations for electrostatics. They follow from Gauss's theorem in differentiated form. Indeed, it is known that 
... At the same time, according to Gauss theory 
(3. 2)
On the other hand, substituting in (3.2) the expression for the differential indicator of the field strength, we obtain
Let's write the sign (-) for the sign of divergence
Instead 
write down its equivalent; instead of div we write (nabla).
or 
(3.3)
Equation (3.3) is called the Poisson equation. A particular form of Poisson's equation when 
, called the Laplace equation:
Operator 
is called the Laplace operator, or Laplacian, and is sometimes denoted by the symbol (delta). Therefore, you can also find the following form of writing the Poisson equation: 
Let's open it in the Cartesian coordinate system. For this purpose, we will write the product of two factors in expanded form:
scalar product,
We carry out term-by-term multiplication and get
Thus, the Poisson equation in a Cartesian coordinate system is written as follows:
Laplace's equation in Cartesian coordinate systems:
Poisson's equation expresses the relationship between the second-order partial derivatives of ___ at any point in the field and the volume density of free charges at this point in the field. At the same time, the potential at any point in the field depends on all charges that create the field, and not only on the magnitude of the free charge.
- Solution uniqueness theory.
The electric field is described by the Laplace or Poisson equations. Both are partial differential equations. Partial differential equations, in contrast to ordinary differential equations, generally have a set of linearly independent solutions. In any concrete practical problem, there is a single picture of the field, that is, a single solution. From the set of linearly independent solutions admitted by the Laplace - Poisson equation, the choice of the only one that satisfies a specific problem is made using boundary conditions. If there is some function that satisfies the Laplace - Poisson equation and boundary conditions in a given field, then this function is the only solution to a specific problem that is being sought. This position is called the unique solution theorem.
- Border conditions.
The boundary conditions are understood as the conditions to which the field at the interface between media with different electrical properties is subject.
When integrating the Laplace (or Poisson) equation, the integration constants are included in the solution. They are determined based on the boundary conditions. Before proceeding to a detailed discussion of the boundary conditions, let us consider the question of the field inside a conducting current under conditions of electrostatics. In a conductive body in an electrostatic field, due to the phenomenon of electrostatic induction, a separation of charges occurs. Negative charges are displaced to the surface of the body, facing towards a higher potential, positive charges - in the opposite direction.
All points of the body will have the same potential. If a potential difference appeared between any points, then under its action an ordered movement of charges would appear, which contradicts the concept of an electrostatic field. The body surface is equipotential. The vector of the external field strength at any point on the surface approaches it at right angles. Inside a conducting body, the field strength is zero, since the external field is compensated by the field of charges located on the surface of the body.
- Conditions at the interface between a conducting body and a dielectric.
At the boundary between a conducting body and a dielectric, in the absence of current through the conducting body, two conditions are met:
1) there is no tangential (tangent to the surface) component of the electric field strength:
2) the vector of electrical displacement at any point of the dielectric immediately adjacent to the surface of the conducting body is numerically equal to the charge density on the surface of the conducting body at this point:
Let's consider the first condition. All points on the surface of a conducting body have the same potential. Consequently, between any two points of the surface that are very close to each other, the potential increment 
, by 
, hence 
i.e increment surface potential equal to zero... Since the element of the path dl between points on the surface is not equal to zero, it is equal to zero.
Proof of the second condition. To do this, mentally select an infinitely small parallelepiped.
Its upper edge is parallel to the surface of the conducting body and is located in the dielectric. The bottom edge is in a conductive body. The height of the parallelepiped is negligible. Let's apply Gauss's theorem to it. Due to the smallness of the linear dimensions, it can be assumed that the charge density at all points on the surface dS of a conducting body that has fallen inside the parallelepiped is the same. The total charge inside the considered volume is 
... Vector flow through the top edge of the volume: 
Due to the smallness of the latter and the fact that the vector ___ slides along them, there is no flow of the vector through the side faces of the volume. There is also no flow through the "bottom" of the volume, since inside the conducting body E \u003d 0 and D \u003d 0 (the conducting body is a finite quantity). 
Thus, the flux of the vector from the volume of the parallelepiped is 
or 
- Conditions at the interface between two dielectrics.
At the interface between two dielectrics with different dielectric constants, two conditions are met:
1) the tangential components of the field strength are equal
2) the normal components of electrical induction are equal
Index 1 refers to the first dielectric, index 2 refers to the second dielectric.
The first condition follows from the fact that in the potential field 
along any closed loop; the second condition is a consequence of Gauss's theorem.
Let us prove the validity of the first condition. For this purpose, select a flat closed contour mnpq and compose the circulation of the electric field strength vector along it.
The top side of the circuit is located in a dielectric with a dielectric constant, the bottom - in a dielectric. The length of the side mn, equal to the length of the side pq, is denoted by. We take the contour so that the sizes np and qm are 
... Therefore, the components of the integral 
along the vertical sides, due to their smallness, we will neglect. Component 
on the path mn is 
, on the path pq is equal to 
... The (-) sign appeared because the length element on the path pq and the tangent component of the vector are directed in opposite directions (clockwise circulation according to the condition) ( 
). Thus or
, as required to prove.
Potentiality condition 
.
To prove the second condition at the interface between two media, we select a very small parallelepiped.
Inside the allocated volume there are bound charges and no free ones, therefore 
(from Gauss's theorem in integral form). Vector stream:
through the top edge with an area: 
;
through the bottom:; 
Hence either 
, as required to prove.
When crossing the boundary separating one dielectric from another, for example, when passing from point n to p, the normal component of the intensity is a finite value, and the path length 
... therefore 
... Therefore, when crossing the interface between two dielectrics, the potential does not undergo jumps.
- Mirror Image Method.
For the calculation of electrostatic fields, limited by any conductive surface of regular shape or in which there are geometrically correct forms the boundary between two dielectrics, the method of mirror images is widely used. This is an artificial method of calculation, in which, in addition to the given charges, additional charges are introduced, the values \u200b\u200band location of which are chosen so as to satisfy the boundary conditions in the field. Territorially, the charges are placed where the mirror (in the geometric sense) representations of the given charges are located. Consider an example of the mirror image method.
Payload axislocated near the conducting plane.
The charged axis (charge per unit length) is located in the dielectric parallel to the surface of the conductive medium (metal wall or ground).
It is required to determine the nature of the field in the upper half-plane (dielectric).
As a result of electrical induction, charges appear on the surface of a conducting body. Their density changes, with a change in the X coordinate. The field in the dielectric is created not only by the charged axis, but also by the charges that have appeared on the surface of the conducting body due to electrostatic induction. Despite the fact that the distribution of the charge density on the surface of the conducting medium is unknown, this problem is relatively easy to solve using the method of mirror images.
We place at point m a fictitious charge of opposite sign (-) with respect to the given charge. The distance h from point m to the plane of separation of the media is the same as the distance from the real charge to the plane of separation. In this sense, a mirror image is realized. Let us make sure that the field strength from two charges and - at any point of the interface has only a component normal to the boundary and does not have a tangential component, since the tangential components from both charges have opposite directions and add up to zero at any point on the surface. The potential of each of the axes is determined by the formula
Where c is the constant of integration
r- distance from the axis
The potential from each of the axes satisfies the Laplace equation in a cylindrical coordinate system
(3.6)
To check, we substitute the right side of the expression in (3.6) and after the transformations we get:
, i.e. 
Since the potential from each of the axes satisfies the Laplace equation and at the same time is satisfied boundary condition (
), then on the basis of the uniqueness theorem the obtained solution is true.
The picture of the field is shown in the figure.
The lines of force are perpendicular to the surface of the wire and the surface of the conducting plane. Signs (-) on the surface of a conductive plane indicate negative charges that have appeared on the surface as a result of electrical induction.
- Basic provisions on the correct picture of the field.
Conditional field types can be divided into three types. Plane-parallel, plane meridian and uniform. A plane-parallel field has a set of equipotential lines of force repeating in all planes perpendicular to any axis of the Cartesian coordinate system. For example, the field of two wire lines. The field potential does not depend on the z coordinate directed along the axis of one of the wires.
The plane-meridian field has a pattern repeating in all meridial planes, that is, the field pattern does not depend on the coordinate ___ of a cylindrical or spherical coordinate system.
A uniform field has the same intensity at all points of the field, that is, its value does not depend on the coordinates of the point. A uniform field forms between the capacitor plates.
- Graphic representation of the pattern of a plane-parallel field.
The analytical calculation of fields is often difficult, for example, when the surface has a complex shape. In this case, the picture of the field is built graphically. For this purpose, it is first found out whether the studied field has symmetry. If it is available, then the field pattern is constructed only for one of the symmetry regions.
Consider the field pattern formed by two mutually perpendicular to the conducting thin plates. Since this field has symmetry, we construct a picture for the upper half-plane. The pattern repeats in the lower half-plane. When building, they are guided by the following rules:
1) the lines of force should approach the surface of the electrodes perpendicularly;
2) lines of force and equipotential lines should be mutually perpendicular and form similar field cells (curvilinear rectangles), for which the ratio of the average cell length to the average width of this cell should be approximately the same, i.e.
If the number of cells in the power tube is denoted by n, and the number of tubes is m (in our example, n \u003d 4, and m \u003d 2 x 6), then, if the listed rules are observed, the potential difference between adjacent equipotentials will be the same and equal 
, where U is the voltage between the electrodes. As long as the vector in each power tube will be the same as in the neighboring one.
The vector flux in each force tube will be the same as in the adjacent one.
The action of some charged bodies on other charged bodies is carried out without their direct contact, by means of an electric field.
The electric field is material. It exists independently of us and our knowledge about it.
An electric field is created by electric charges and is detected using electric charges by the action of a certain force on them.
The electric field propagates at a final speed of 300,000 km / s in a vacuum.
Since one of the main properties of an electric field is its action on charged particles with a certain strength, then to introduce the quantitative characteristics of the field, it is necessary to place a small body with a charge q (test charge) at the investigated point in space. A force will act on this body from the side of the field
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If you change the value of the test charge, for example, twice, the force acting on it will also change twice.
When the value of the test charge changes by n times, the force acting on the charge also changes by n times.
The ratio of the force acting on a test charge placed at a given point of the field to the value of this charge is a constant value and does not depend either on this force, or on the magnitude of the charge, or on whether there is any charge. This ratio is designated by a letter and is taken as the strength characteristic of the electric field. The corresponding physical quantity called electric field strength .
Tension shows what force acts from the side of the electric field on a unit charge placed at a given point in the field.
To find the unit of tension, it is necessary to substitute units of force - 1 N and charge - 1 C into the determining equation of tension. We get: [E] \u003d 1 N / 1 Cl \u003d 1 N / Cl.
For clarity, electric fields in the drawings are depicted using ley lines.
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An electric field can do the work of moving a charge from one point to another. Hence, a charge placed at a given point of the field has a reserve of potential energy.
The energy characteristics of the field can be entered similarly to the introduction of the force characteristic.
When the value of the test charge changes, not only the force acting on it changes, but also the potential energy of this charge. The ratio of the energy of the test charge located at a given point of the field to the value of this charge is a constant value and does not depend on either the energy or the charge.
To get a unit of potential, it is necessary to substitute units of energy - 1 J and charge - 1 C into the governing equation of potential. We get: [φ] \u003d 1 J / 1 C \u003d 1 V.
This unit has its own name of 1 volt.
The potential of the field of a point charge is directly proportional to the magnitude of the charge that creates the field and is inversely proportional to the distance from the charge to a given point of the field:
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Electric fields in the drawings can also be depicted using surfaces of equal potential, called equipotential surfaces .
When an electric charge moves from a point with one potential to a point with a different potential, work is done.
Physical quantity, equal ratio work on moving a charge from one point of the field to another, to the magnitude of this charge, is called electrical voltage :
Voltage shows what the work done by an electric field is equal to when a charge of 1 C is moved from one point of the field to another.
The unit of voltage, as well as potential, is 1 V.
The voltage between two field points located at a distance d from each other is related to the field strength: 
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In a uniform electric field, the work of moving a charge from one point of the field to another does not depend on the shape of the trajectory and is determined only by the magnitude of the charge and the potential difference between the points of the field.
All bodies in nature are capable of electrifying, i.e. acquire an electric charge. The presence of an electric charge manifests itself in the fact that a charged body interacts with other charged bodies. There are two types of electric charges, conventionally called positive and negative. Like charges repel, unlike charges attract.
Electric charge is an inherent property of some elementary particles... The charge of all charged elementary particles is the same in absolute value and is equal to 1.6 × 10 –19 C. The carrier of an elementary negative electric charge is, for example, an electron. The proton carries a positive charge, the neutron has no electric charge. The atoms and molecules of all substances are built from protons, neutrons and electrons. Usually, protons and electrons are present in equal amounts and distributed in matter with the same density, so the bodies are neutral. The electrification process consists in creating an excess of particles of the same sign in the body or in their redistribution (creating an excess of charge of the same sign in one part of the body; while the body as a whole remains neutral).
The interaction between resting electric charges takes place through a special form of matter called electric field ... Any charge changes the properties of the surrounding space - it creates an electrostatic field in it. This field manifests itself in a forceful action on any electric charge placed in any of its points. Experience shows that the ratio of the force acting on a point charge qplaced at a given point of the electrostatic field, the magnitude of this charge for all charges is the same. This relationship is called tensions electric field and is its power characteristic:
Empirically it was found that for the electrostatic field, superposition principle : the electrostatic field generated by several charges is equal to the vector sum of the electrostatic fields generated by each charge separately:
Charges placed in an electrostatic field have potential energy. Experience shows that the ratio of potential energy W positive point charge qplaced at a given point of the field, to the magnitude of this charge there is a constant value. This ratio is the energy characteristic of the electrostatic field and is called potential :
φ = W / q. (2.6.7)
The potential of an electrostatic field is numerically equal to the work that the field forces do over a unit positive charge when it is removed from a given point to infinity. The unit is volt (V). Two characteristics of the electrostatic field - intensity and potential are related by the relationship [cf. with expression (2.6.4)]
The minus sign indicates that the vector of the electric field strength is directed towards a decrease in the potential. Note that if in some region of space the potentials of all points have the same potential, then
The electrostatic field can also be represented graphically using lines of force and equipotential surfaces.
Power lineelectric field is called an imaginary line, the tangent to which at each point coincides with the direction of the intensity vector. The lines of force of the electrostatic field are open : they can begin or end only on charges, or go to infinity.
To graphically display the potential distribution of the electrostatic field, use equipotential surfaces - surfaces, at all points of which the potential has the same value.
It is easy to show that the line of force of the electrostatic field always intersects the equipotential surface at a right angle. Figure 10 shows the lines of force and equipotential surfaces of point electric charges.
Figure 10 - Lines of force and equipotential surfaces of point charges
A magnetic field
Experience shows that just as an electrostatic field arises in the space surrounding electric charges, a force field arises in the space surrounding currents and permanent magnets, called magnetic . The presence of a magnetic field is detected by the forceful action on the conductors with current and permanent magnets introduced into it. The name “magnetic field” is associated with the fact of the orientation of the magnetic needle under the action of the field created by the current (H. Oersted, 1820).
An electric field acts both on stationary and on electric charges moving in it. The most important feature of a magnetic field is that it acts only on electric charges moving in this field.
Experience shows that the magnetic field has an orienting effect on the magnetic needle and the frame with the current, turning them in a certain way. The direction of the magnetic field at a given point is taken as the direction along which the axis of the thin magnetic arrow is freely set in the direction from south to north or the positive normal to a flat contour with current.
The quantitative characteristic of the magnetic field is vector of magnetic induction ... The magnetic induction at a given point is numerically equal to the maximum torque acting on a flat frame with a current with a magnetic moment p m \u003d 1 A × m 2:
B \u003d M max / p m. (2.6.9)
It has been experimentally established that for a magnetic field it is also true superposition principle : the magnetic field generated by several moving charges (currents) is equal to the vector sum of the magnetic fields generated by each charge (current) separately.
Electrostatic field electrostatic field
electric field of stationary electric charges.
ELECTROSTATIC FIELDELECTROSTATIC FIELD, the electric field of stationary and unchanging electric charges over time, which interacts between them.
An electrostatic field is characterized by an electric field strength (cm. ELECTRIC FIELD VOLTAGE) E, which is its strength characteristic: The strength of the electrostatic field shows with what force the electrostatic field acts on a single positive electric charge (cm. ELECTRIC CHARGE)placed at a given point in the field. The direction of the tension vector coincides with the direction of the force acting on the positive charge, and opposite to the direction of the force acting on the negative charge.
An electrostatic field is stationary (constant) if its strength does not change over time. Stationary electrostatic fields are created by stationary electric charges.
An electrostatic field is homogeneous if the vector of its intensity is the same at all points of the field, if the vector of intensity at different points is different, the field is inhomogeneous. Homogeneous electrostatic fields are, for example, the electrostatic fields of a uniformly charged finite plane and a flat capacitor (cm. CONDENSER (electric)) away from the edges of its plates.
One of the fundamental properties of the electrostatic field is that the work of the forces of the electrostatic field when the charge moves from one point of the field to another does not depend on the trajectory of motion, but is determined only by the position of the starting and ending points and the magnitude of the charge. Consequently, the work of the forces of the electrostatic field when the charge moves along any closed trajectory is zero. Force fields with this property are called potential or conservative. That is, the electrostatic field is a potential field, the energy characteristic of which is the electrostatic potential (cm. ELECTROSTATIC POTENTIAL) associated with the vector of intensity E by the ratio:
E \u003d -gradj.
Force lines are used to graphically represent the electrostatic field. (cm. POWER LINES) (tension lines) - imaginary lines, tangents to which coincide with the direction of the intensity vector at each point of the field.
For electrostatic fields, the principle of superposition is observed (cm. SUPERPOSITION PRINCIPLE)... Each electric charge creates an electric field in space, regardless of the presence of other electric charges. The strength of the resulting field created by the system of charges is equal to the geometric sum of the strengths of the fields created at a given point by each of the charges separately.
Any charge in the surrounding space creates an electrostatic field. To detect the field at any point, it is necessary to place a point test charge at the observation point - a charge that does not distort the investigated field (does not cause a redistribution of charges that create the field).
The field created by a solitary point charge q is spherically symmetric. Tension modulus of a solitary point charge in vacuum using Coulomb's law (cm. PENDANT LAW) can be represented as:
E \u003d q / 4pe about r 2.
Where e about - electrical constant, \u003d 8.85. 10 -12 F / m.
Coulomb's law, established with the help of the torsion balance created by him (see. Coulomb scales (cm. PENDANT LIBRA)), is one of the basic laws describing the electrostatic field. It establishes the relationship between the force of interaction of charges and the distance between them: the force of interaction of two point stationary charged bodies in a vacuum is directly proportional to the product of the moduli of charges and inversely proportional to the square of the distance between them.
This force is called Coulomb, and the field is called Coulomb. In a Coulomb field, the direction of the vector depends on the sign of the charge Q: if Q\u003e 0, then the vector is directed along the radius from the charge, if Q ( cm. DIELECTRIC PERMEABILITY) of the medium) is less than in a vacuum.
The experimentally established Coulomb's law and the principle of superposition make it possible to fully describe the electrostatic field of a given system of charges in a vacuum. However, the properties of the electrostatic field can be expressed in another, more general formwithout resorting to the concept of the Coulomb field of a point charge. The electric field can be characterized by the value of the flux of the electric field strength vector, which can be calculated in accordance with the Gauss theorem (cm. GAUSS'S THEOREM)... Gauss's theorem establishes a relationship between the flow of electric field strength through a closed surface and the charge inside this surface. The intensity flux depends on the distribution of the field over the surface of a particular area and is proportional to the electric charge inside this surface.
If an insulated conductor is placed in an electric field, then a force will act on the free charges q in the conductor. As a result, a short-term movement of free charges occurs in the conductor. This process will end when the intrinsic electric field of the charges that have arisen on the surface of the conductor completely compensates for the external field, that is, an equilibrium distribution of charges is established, at which the electrostatic field inside the conductor turns to zero: at all points inside the conductor E \u003d 0, then there is no field. The lines of force of the electrostatic field outside the conductor in the immediate vicinity of its surface are perpendicular to the surface. If this were not so, then there would be a component of the field strength, a current would flow along the surface of the conductor and along the surface. The charges are located only on the surface of the conductor, while all points on the surface of the conductor have the same potential value. The surface of the conductor is the equipotential surface (cm. EQUIPOTENTIAL SURFACE)... If there is a cavity in the conductor, then the electric field in it is also zero; the electrostatic protection of electrical devices is based on this.
If a dielectric is placed in an electrostatic field, then a polarization process occurs in it - the process of orientation of dipoles (cm. DIPOLE) or the appearance of dipoles oriented along the field under the influence of an electric field. In a homogeneous dielectric, the electrostatic field due to polarization (see Polarization of dielectrics) decreases in? time.
encyclopedic Dictionary. 2009 .
See what "electrostatic field" is in other dictionaries:
electrostatic field - Electric field of stationary charged bodies in the absence of electric currents in them. [GOST R 52002 2003] electrostatic field Electric field of stationary electric charges. The principles of the field in question are used to create ... ... Technical translator's guide
Electrostatic field - a set of phenomena associated with the emergence, conservation and relaxation of a free electric charge on the surface and volume of substances, materials, products. A source … Dictionary-reference book of terms of normative and technical documentation
Electrostatic field is a field created by electric charges that are stationary in space and constant in time (in the absence of electric currents). An electric field is a special type of matter associated with electric ... ... Wikipedia
Electric. field of motionless electrics. charges, carrying out the take-off between them. As well as perm. electric field, E. p. is characterized by the intensity of the electric. field K is the ratio of the force acting from the field on the charge to the value of the charge. Power ... Physical encyclopedia
The electric field of stationary electric charges ... Big Encyclopedic Dictionary
Electrostatic field - a set of phenomena associated with the emergence, preservation and relaxation of a free electric charge on the surface and volume of substances, materials, products ... Source: MSanPiN 001 96. Sanitary standards for permissible levels of physical factors ... Official terminology
electrostatic field - elektrostatinis laukas statusas T sritis Standartizacija ir metrologija apibrėžtis Apibrėžtį žr. priede. priedas (ai) Grafinis formatas atitikmenys: angl. electrostatic field vok. elektrostatisches Feld, n rus. electrostatic field, n pranc. ... ...
electrostatic field - elektrostatinis laukas statusas T sritis Standartizacija ir metrologija apibrėžtis Nejudančių elektringųjų dalelių elektrinis laukas. atitikmenys: angl. electrostatic field vok. elektrostatisches Feld, n rus. electrostatic field, n pranc. ... ... Penkiakalbis aiškinamasis metrologijos terminų žodynas
electrostatic field - elektrostatinis laukas statusas T sritis fizika atitikmenys: angl. electrostatic field vok. elektrostatisches Feld, n rus. electrostatic field, n pranc. champ électrostatique, m ... Fizikos terminų žodynas
The electric field of stationary electric charges, which interacts between them. Like an alternating electric field, an electric field is characterized by the strength of the electric field E: the ratio of the force acting on the charge to ... ... Great Soviet Encyclopedia
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- New ideas in physics. Issue 3. The principle of relativity. 1912, Borgman I.I. , The wave theory of sv * that considers that the manifestation of sv 1\u003e ma is due to vibrations propagating in the form of * waves in the space surrounding the s * t * la t * la; as soon * it turned out ... Category: Mathematics and Science Series: Publisher: YoYo Media,
The entire surrounding space is permeated by electromagnetic fields.
There are natural and man-made sources of electromagnetic fields.
Natural sources of electromagnetic field:
- atmospheric electricity;
- radio emission from the Sun and galaxies ( relict radiationuniformly distributed in the Universe);
- electric and magnetic fields of the Earth.
Sources technogenic electromagnetic fields are various transmitting equipment, switches, separating high-frequency filters, antenna systems, industrial installations equipped with high-frequency (HF), ultra-high-frequency (UHF) and microwave (microwave) generators.
Sources of electromagnetic fields in production
There are two large groups of sources of EMF in production:
Dangerous effects on workers can be caused by:
- RF EMF (60 kHz - 300 GHz),
- electric and magnetic fields of industrial frequency (50 Hz);
- electrostatic fields.
Sources of radio frequency waves are primarily radio and television broadcasting stations. The radio frequency classification is given in table. 1. The effect of radio waves largely depends on the characteristics of their propagation. It is influenced by the nature of the relief and cover of the Earth's surface, large objects and structures located on the way, etc. Forests and uneven terrain absorb and scatter radio waves.
Table 1. RF range
Electrostatic fieldsare created in power plants and during electrical processes. Depending on the sources of formation, they can exist in the form of an electrostatic field itself (a field of stationary charges). In industry, electrostatic fields are widely used for electro-gas cleaning, electrostatic separation of ores and materials, electrostatic application of paints and varnishes and polymer materials. Static electricity is generated during the manufacture, testing, transportation and storage of semiconductor devices and integrated circuits, grinding and polishing of cases for radio and television receivers, in the rooms of computer centers, in duplicating equipment, as well as in a number of other processes where dielectric materials are used. Electrostatic charges and the electrostatic fields created by them can arise when dielectric fluids and some bulk materials move through pipelines, pouring dielectric fluids, or rolling film or paper into a roll.
Magnetic fields are created by electromagnets, solenoids, capacitor-type installations, cast and sintered magnets, and other devices.
Sources of electric fields
Any electromagnetic phenomenon, considered as a whole, is characterized by two sides - electrical and magnetic, between which there is a close connection. The electromagnetic field also always has two interconnected sides - the electric field and the magnetic field.
A source of industrial frequency electric fields are the current-carrying parts of operating electrical installations (power lines, inductors, capacitors of thermal installations, feeder lines, generators, transformers, electromagnets, solenoids, half-period or capacitor-type pulse installations, cast and sintered magnets, etc.). Long-term exposure to an electric field on the human body can cause disruption of the functional state of the nervous and cardiovascular systems, which is expressed in increased fatigue, decreased quality of work, pain in the heart, changes in blood pressure and pulse.
For an electric field of industrial frequency in accordance with GOST 12.1.002-84, the maximum permissible level of electric field strength, in which it is not allowed to stay in which without the use of special protective equipment during the entire working day, is 5 kV / m. In the interval over 5 kV / m to 20 kV / m inclusive, the permissible residence time T (h) is determined by the formula T \u003d 50 / E - 2, where E is the intensity of the acting field in the controlled area, kV / m. With a field strength above 20 kV / m up to 25 kV / m, the time spent by personnel in the field should not exceed 10 minutes. The maximum permissible value of the electric field strength is set equal to 25 kV / m.
If it is necessary to determine the maximum permissible electric field strength for a given residence time in it, the intensity level in kV / m is calculated using the formula E - 50 / (T + 2), where T is the time spent in the electric field, h.
The main types of collective protection means against the effects of an electric field of industrial frequency currents are shielding devices - an integral part of an electrical installation designed to protect personnel in open switchgears and on overhead power lines (Fig. 1).
The shielding device is necessary when inspecting equipment and during operational switching, monitoring the production of work. Structurally, shielding devices are made in the form of canopies, awnings or partitions made of metal ropes. rods, nets. Shielding devices must be anti-corrosive and grounded.
Figure: 1. Shielding canopy over the passage to the building
To protect against the influence of an electric field of industrial frequency currents, shielding suits are also used, which are made of a special fabric with metallized threads.
Sources of electrostatic fields
At enterprises, substances and materials with dielectric properties are widely used and obtained, which contributes to the generation of static electricity charges.
Static electricity is generated by friction (contact or separation) of two dielectrics against each other, or dielectrics against metals. At the same time, electric charges can accumulate on the rubbing substances, which easily drain into the ground if the body is a conductor of electricity and it is grounded. On dielectrics, electric charges are held for a long time, as a result of which they are called static electricity.
The process of the appearance and accumulation of electric charges in substances is called electrification.
The phenomenon of static electrification is observed in the following main cases:
- in the stream and when splashing liquids;
- in a stream of gas or steam;
- upon contact and subsequent removal of two solid
- dissimilar bodies (contact electrification).
A discharge of static electricity occurs when the intensity of the electrostatic field above the surface of a dielectric or conductor, due to the accumulation of charges on them, reaches a critical (breakdown) value. For air, the breakdown voltage is 30 kV / cm.
People working in the area affected by the electrostatic field have a variety of disorders: irritability, headache, sleep disturbances, decreased appetite, etc.
Permissible levels of intensity of electrostatic fields are established by GOST 12.1.045-84 “Electrostatic fields. Permissible levels at workplaces and requirements for control ”and the Sanitary and Hygienic Standards for Permissible Electrostatic Field Strength (GN 1757-77).
These regulatory legal acts apply to electrostatic fields created during the operation of high-voltage direct current electrical installations and electrification of dielectric materials, and establish permissible levels of intensity of electrostatic fields at personnel workplaces, as well as general requirements for monitoring and protective equipment.
Permissible levels of intensity of electrostatic fields are set depending on the time spent at the workplace. The maximum permissible level of intensity of electrostatic fields is 60 kV / m for 1 hour.
When the intensity of electrostatic fields is less than 20 kV / m, the residence time in electrostatic fields is not regulated.
In the voltage range from 20 to 60 kV / m, the permissible time spent by personnel in an electrostatic field without protective equipment depends on the specific voltage level at the workplace.
Measures of protection against static electricity are aimed at preventing the occurrence and accumulation of static electricity charges, creating conditions for the dissipation of charges and eliminating the danger of their harmful effects. Basic protection measures:
- prevention of the accumulation of charges on electrically conductive parts of the equipment, which is achieved by grounding equipment and communications, on which charges may appear (devices, tanks, pipelines, conveyors, unloading devices, overpasses, etc.);
- reducing the electrical resistance of the processed substances;
- the use of static electricity neutralizers, which create positive and negative ions near electrified surfaces. Jonah, charge carriers, opposite to the surface charge, are attracted to it, and neutralize the charge. According to the principle of operation, neutralizers are divided into the following types: corona discharge (induction and high voltage), radioisotope, the action of which is based on the ionization of air by alpha radiation from plutonium-239 and beta radiation from promethium-147, aerodynamic, representing an expander chamber, in which using ionizing radiation or corona discharge, ions are generated, which are then supplied by an air stream to the place of formation of static charges;
- reducing the intensity of static electricity. It is achieved by appropriate selection of the speed of movement of substances, excluding spraying, crushing and spraying of substances, removal of electrostatic charge, selection of friction surfaces, cleaning combustible gases and liquids from impurities;
- drainage of static electricity charges that accumulate on people. This is achieved by providing workers with conductive footwear and antistatic gowns, the device of electrically conductive floors or earthed areas, platforms and work platforms. grounding of door handles, handrails of stairs, handles of devices, machines and apparatus.
Sources of magnetic field
Power frequency magnetic fields (MF) arise around any electrical installations and power frequency conductors. The higher the current, the higher the intensity of the magnetic field.
Magnetic fields can be constant, pulsed, infra-low-frequency (up to 50 Hz), variable. The action of the MP can be continuous and intermittent.
The degree of MF impact depends on its maximum strength in the working space of a magnetic device or in the zone of influence of an artificial magnet. The dose received by a person depends on the location of the workplace in relation to the MP and the mode of work. Constant MPs do not cause any subjective influences. Under the action of variable MF, characteristic visual sensations, the so-called phosphenes, are observed, which disappear at the moment of cessation of exposure.
With constant work under conditions of exposure to MF that exceed the maximum permissible levels, dysfunctions of the nervous, cardiovascular and respiratory systems, the digestive tract, and changes in blood composition develop. With a predominantly local impact, vegetative and trophic disorders can occur, as a rule, in the area of \u200b\u200bthe body that is under the direct influence of the MP (most often the hands). They are manifested by a feeling of itching, pallor or cyanosis of the skin, swelling and thickening of the skin, in some cases, hyperkeratosis (keratinization) develops.
The strength of the MP at the workplace should not exceed 8 kA / m. The strength of a MP power transmission line with a voltage of up to 750 kV usually does not exceed 20-25 A / m, which does not pose a danger to humans.
Sources of electromagnetic radiation
Sources of electromagnetic radiation in a wide frequency range (super- and infra-low-frequency, radio frequency, infrared, visible, ultraviolet, X-ray - Table 2) are powerful radio stations, antennas, microwave generators, induction and dielectric heating installations, radars, lasers, measuring and monitoring devices, research installations, medical high-frequency devices and devices, personal electronic computers (PC), video display terminals on cathode-ray tubes, used both in industry, scientific research, and in everyday life.
Microwave ovens, televisions, mobile phones and cordless telephones are also sources of increased electromagnetic radiation hazards.
Table 2. Spectrum of electromagnetic radiation
Low frequency radiation
Production systems are sources of low frequency radiation. transmission and distribution of electricity (power plants, transformer substations, power transmission systems and lines), power grids of residential and office buildings, electrically driven transport and its infrastructure.
Prolonged exposure to low-frequency radiation may cause headaches, changes in blood pressure, fatigue develop, hair loss, brittle nails, weight loss, and a persistent decrease in working capacity may occur.
To protect against low-frequency radiation, either radiation sources (Fig. 2) or areas where a person can be shielded.
Figure: 2. Shielding: a - inductor; b - capacitor
Sources of radio frequency radiation
The source of RF EMF are:
- in the range of 60 kHz - 3 MHz - unshielded elements of equipment for induction processing of metal (injection, annealing, melting, soldering, welding, etc.) and other materials, as well as equipment and devices used in radio communication and broadcasting;
- in the range 3 MHz - 300 MHz - unshielded elements of equipment and devices used in radio communications, broadcasting, television, medicine, as well as equipment for heating dielectrics;
- in the range of 300 MHz - 300 GHz - unshielded elements of equipment and instruments used in radar, radio astronomy, radio spectroscopy, physiotherapy, etc. Long-term exposure to radio waves on various systems of the human body causes different consequences.
The most characteristic deviations in the central nervous system and the human cardiovascular system when exposed to radio waves of all ranges are. Subjective complaints - frequent headache, drowsiness or insomnia, fatigue, weakness, excessive sweating, memory loss, distraction, dizziness, darkening of the eyes, an unreasonable feeling of anxiety, fear, etc.
The influence of the electromagnetic field of the medium-wave range with prolonged exposure to is manifested in excitatory processes, violation of positive reflexes. Changes in the blood are noted, up to leukocytosis. Dysfunction of the liver, dystrophic changes in the brain, internal organs and the reproductive system.
The short-wave electromagnetic field provokes changes in the adrenal cortex, cardiovascular system, bioelectrical processes of the cerebral cortex.
VHF EMF causes functional changes in the nervous, cardiovascular, endocrine and other systems of the body.
The degree of danger of exposure to a person of microwave radiation depends on the power of the source of electromagnetic radiation, the mode of operation of the emitters, design features of the emitting device, EMF parameters, energy flux density, field strength, exposure time, size of the irradiated surface, individual properties of a person, location of workplaces and efficiency protective measures.
Distinguish between thermal and biological impact Microwave radiation.
The thermal effect is a consequence of the absorption of the energy of the EMF of microwave radiation. The higher the field strength and the longer the exposure time, the more pronounced the thermal effect. When the energy flux density is W - 10 W / m2, the body cannot cope with heat removal, the body temperature rises and irreversible processes begin.
The biological (specific) effect is manifested in the weakening of the biological activity of protein structures, disruption of the cardiovascular system and metabolism. This effect is manifested when the EMF intensity is less than the thermal threshold, which is equal to 10 W / m 2.
Exposure to EMF microwave radiation is especially harmful to tissues with an underdeveloped vascular system or insufficient blood circulation (eyes, brain, kidneys, stomach, gall and bladder). Irradiation of the eyes can lead to clouding of the lens (cataracts) and burns to the cornea.
To ensure the safety of work by sources of electromagnetic waves, a systematic control of the actual standardized parameters is carried out at workplaces and in places where personnel may be located. The control is carried out by measuring the strength of the electric and magnetic fields, as well as by measuring the energy flux density.
Protection of personnel from exposure to radio waves is applied in all types of work if the working conditions do not meet the requirements of the standards. This protection is carried out in the following ways:
- matched loads and power absorbers that reduce the strength and density of the field of the energy flux of electromagnetic waves;
- shielding of the workplace and radiation source;
- rational placement of equipment in the workroom;
- selection of rational operating modes of equipment and personnel working regime.
The most efficient use of matched loads and power absorbers (antenna equivalents) in the manufacture, tuning and testing of individual blocks and complexes of equipment.
An effective means of protection against the effects of electromagnetic radiation is the shielding of radiation sources and the workplace with screens that absorb or reflect electromagnetic energy. The choice of screen design depends on the nature of the technological process, source power, and wavelength range.
Reflective screens are made of highly conductive materials such as metals (solid walls) or cotton fabrics with a metal backing. Solid metal shields are the most effective and even at a thickness of 0.01 mm provide an attenuation of the electromagnetic field by about 50 dB (100,000 times).
Materials with poor electrical conductivity are used for the manufacture of absorbing screens. Absorbent screens are made in the form of compressed rubber sheets of a special composition with conical solid or hollow spikes, as well as in the form of porous rubber plates filled with carbonyl iron with an pressed-in metal mesh. These materials are glued to the frame or to the surface of the radiating equipment.
An important preventive measure for protection against electromagnetic radiation is the fulfillment of the requirements for the placement of equipment and for the creation of premises in which sources of electromagnetic radiation are located.
Protection of personnel from overexposure can be achieved by placing HF, UHF and microwave generators, as well as radio transmitters in specially designed rooms.
The screens of radiation sources and workplaces are blocked with disconnecting devices, which makes it possible to exclude the operation of the radiation equipment when the screen is open.
The permissible levels of exposure to workers and the requirements for monitoring at workplaces for electromagnetic fields of radio frequencies are set out in GOST 12.1.006-84.