Dielectrics and their types conductors semiconductors presentation. Presentation "Conductors and dielectrics in an electrostatic field" presentation for a lesson in physics (Grade 10) on the topic. structure of the salt molecule
- What is an electric field?
- What are the main properties of the electrostatic field.
- What generates an electric field?
- What is called electric field strength?
- What electric field is called uniform?
- How can a uniform electric field be obtained?
- How are the lines of force of a uniform electric field directed?
- How to calculate the strength of the electric field created by a point charge?
Conductors and dielectrics in an electrostatic field
Lecture plan:
- 1. Conductors and dielectrics.
- 2. Conductors in an electrostatic field.
- 3. Dielectrics in an electrostatic field.
Two types of dielectrics.
- 4. Dielectric constant.
The structure of metals
The last electron is weakly attracted to the nucleus because:
- far from the core
- 10 electrons repel the eleventh
the last electron is detached from the nucleus and becomes free
substances by conductivity
conductors
- conductors
dielectrics
are substances that do not conduct electricity
no free charges
are substances that conduct electricity
there are free charges
The structure of metals
The structure of metals
E internal
E ext.= E internal
Metal conductor in an electrostatic field
E ext.= E internal
E common =0
CONCLUSION:
There is no electric field inside the conductor.
The entire static charge of a conductor is concentrated on its surface.
The structure of the dielectric
structure of the salt molecule
electric dipole -
a set of two point charges that are equal in absolute value and opposite in sign.
The structure of a polar dielectric
Dielectric in an electric field
E internal E external .
E ext.
E internal
CONCLUSION:
DIELECTRIC WEAKEN THE EXTERNAL ELECTRIC FIELD
Galimurza S.A.
Dielectric constant of the medium
Electric field strength in vacuum
Electric field strength in a dielectric
Dielectric constant of the medium
E about
To the directory:
- Coulomb's law:
- The strength of the electric field created by a point charge:
q 1 q 2
r
2
q
r
2
What are microwaves?
Household microwave ovens use electromagnetic waves with a frequency of 2450 MHz - microwaves.
In such microwaves, the electric field 2 · 2 450 000 000 changes direction every second.
Microwave: microwave frequency 2450 MHz
How do microwaves heat food?
Heating of products occurs due to two physical mechanisms:
1. microwave heating of the surface layer
2. subsequent penetration of heat into the depth of the product due to thermal conductivity.
device
power,
frequency,
microwave
mobile phone
GSM class 4
mobile phone
1. In the absence of an external field, the particles are distributed inside the substance so that the electric field they create is zero. 2. In the presence of an external field, a redistribution of charged particles occurs, and an own electric field arises in the substance, which is the sum of the external E0 field and the internal E / created by the charged particles of the substance? What substances are called conductors? 3. Conductors -
- substances with the presence of free charges that participate in thermal motion and can move throughout the volume of the conductor
- 4. In the absence of an external field in the "-" conductor, the free charge is compensated by the "+" charge of the ionic lattice. In an electric field, there redistribution free charges, as a result of which uncompensated "+" and "-" charges appear on its surface
- This process is called electrostatic induction, and the charges that appeared on the surface of the conductor are induction charges.
- 8. There are no free electric charges in dielectrics (insulators). They are composed of neutral atoms or molecules. Charged particles in a neutral atom are bound to each other and cannot move under the action of an electric field throughout the entire volume of the dielectric.
- water, alcohol,
- nitric oxide (4)
- inert gases, oxygen, hydrogen, benzene, polyethylene.
- A) Potential energy of charges
- B) Kinetic energy of charges
- B) zero
- A) These are substances in which charged particles cannot move under the influence of an electric field.
- B) These are substances in which charged particles can move under the influence of an electric field.
- A) This is the displacement of positive and negative bound charges of the dielectric in opposite directions
- B) This is the displacement of the positive and negative bound charges of the dielectric in one direction
- C) This is the arrangement of positive and negative charges of the dielectric in the middle
- A) inside the conductor
- B) on its surface
- 8. Non-polar dielectrics, these are dielectrics in which the centers of distribution of positive and negative charges ...
- A) On the fact that the electric field inside the conductor is maximum.
- B) on the fact that there is no electric field inside the conductor
- A) It is a positively charged system of charges
- B) It is a negatively charged system of charges
- B) This neutral system of charges
On the surface of the sphere, the cones cut out small spherical sections and which can be considered flat. A r1r1 r2r2 S1S1 S2S2, or The cones are similar to each other, since the angles at the vertex are equal. It follows from the similarity that the areas of the bases are related as the squares of the distances and from point A to the sites and, respectively. Thus,
Equipotential surfaces An approximate course of equipotential surfaces for a certain moment of excitation of the heart is shown in the figure. In an electric field, the surface of a conducting body of any shape is an equipotential surface. The dotted lines indicate the equipotential surfaces, the numbers next to them indicate the potential value in millivolts.
Dielectric constant of substances Substance ε ε Gases and water vapor Nitrogen Hydrogen Air Vacuum Water vapor (at t=100 ºС) Helium Oxygen Carbon dioxide Liquids Liquid nitrogen (at t= -198.4 ºС) Gasoline Water Liquid hydrogen (at t= -252, 9 ºС) Liquid helium (at t= -269 ºC) Glycerin 1.0058 1.006 1.4 1.9–2.0 81 1.2 1.05 43 Liquid oxygen (at t= -192.4 ºС) Transformer oil Alcohol Ether Solids Diamond Waxed paper Dry wood Ice (at t= –10 ºС) Paraffin Rubber Mica Glass Barium titanium Porcelain Amber 1.5 2.2 26 4.3 5.7 2.2 2.2–3.7 70 1.9–2.2 3.0–6.0 5.7–7.2 6.0–10.4–6.8 2.8
Literature O. F. Kabardin “Physics. Reference materials". O. F. Kabardin “Physics. Reference materials". A. A. Pinsky “Physics. Textbook for grade 10 schools and classes with in-depth study of physics. A. A. Pinsky “Physics. Textbook for grade 10 schools and classes with in-depth study of physics. G. Ya. Myakishev “Physics. Electrodynamics classes. G. Ya. Myakishev “Physics. Electrodynamics classes. Journal "Quantum". Journal "Quantum".
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Presentation on the topic: Dielectric
slide number 1
Description of the slide:
ELECTROSTATIC FIELD IN DIELECTRICS Types of dielectrics and their polarization Dielectrics are substances in which there are practically no free charge carriers. Dielectrics do not conduct electricity under normal conditions. The term "dielectrics" was introduced by Faraday. Ideal dielectrics do not exist in nature, since all substances conduct electric current to some extent. Dielectrics conduct electric current by about 15 to 20 orders of magnitude worse than substances called conductors. A dielectric, like any substance, consists of atoms and molecules. Dielectric molecules are electrically neutral. The positive charge of all the nuclei of the molecule is equal to the total charge of the electrons. A molecule can be considered as an electric dipole with an electric moment, where Q is the total positive charge of atomic nuclei in the molecule, l is a vector drawn from the "center of gravity" of the negative charges of electrons in the molecule to the "center of gravity" of positive charges - atomic nuclei. 900game.net
slide number 2
Description of the slide:
A dielectric is called non-polar (with a covalent non-polar chemical bond between atoms in molecules) if, in the absence of an external electric field, the "centers of gravity" of positive and negative charges in the molecules coincide, and, therefore, the electric moment p of the molecules of such dielectrics is zero (an example is: N2 , H2, O2, CO2, CH4). Under the action of an external electric field, the charges of nonpolar molecules are shifted in opposite directions (positive - along the field, negative - against the field) and the molecules acquire a dipole moment.
slide number 3
Description of the slide:
A dielectric is called polar (with a covalent polar chemical bond between atoms in molecules), if even in the absence of an external electric field, the "centers of gravity" of positive and negative charges do not coincide. The molecules of such dielectrics always have a dipole moment. An example of such molecules are: H2O, NH3, SO2, CO. In the absence of an external field, the dipole moments of polar molecules are randomly oriented in space due to thermal motion, and their resulting moment is zero. If such a dielectric is placed in an external field, then the forces of this field will tend to rotate the dipoles along the field, and a nonzero resulting dipole moment arises.
slide number 4
Description of the slide:
A dielectric is called ionic, the molecules of which have an ionic (crystalline) structure (examples: NaCl, KS1, KBr). Ionic crystals are spatial lattices with the correct alternation of ions of different signs. In these crystals, it is impossible to isolate individual molecules, and the crystals can be considered as a system of two ionic sublattices pushed one into the other. When an electric field is applied to an ionic crystal, some deformation of the crystal lattice or a relative displacement of the sublattices occurs, leading to the appearance of dipole moments.
slide number 5
Description of the slide:
When all three groups of dielectrics are introduced into an external magnetic field, dielectric polarization occurs - the process of dipole orientation or the appearance of field-oriented dipoles under the influence of an external electric field. As a result, a non-zero total dipole moment of the dielectric molecules arises.
slide number 6
Description of the slide:
According to the three groups of dielectrics, three types of polarization are distinguished: electronic, or deformation, polarization of a dielectric with nonpolar molecules. consisting in the occurrence of an induced dipole moment in atoms due to the deformation of electron orbits; orientational, or dipole, polarization of a dielectric with polar molecules, which consists in the orientation of the available dipole moments of molecules along the field. Thermal motion prevents the complete orientation of molecules, but as a result of the combined action of both factors (electric field and thermal motion), a preferential orientation of the dipole moments of molecules along the field arises. This orientation is the stronger, the greater the electric field strength and the lower the temperature; ionic polarization of dielectrics with ionic crystal lattices. consisting in the displacement of the sublattice of positive ions along the field, and negative - against the field, leading to the appearance of dipole moments.
slide number 7
Description of the slide:
Polarization. Field strength in a dielectric The polarization of a dielectric is characterized by a vector quantity - the polarization determined by the dipole moment of a unit volume of the dielectric: æ is a dimensionless quantity, and always æ > 0 and for most dielectrics (solid and liquid) is several units. is the dipole moment of the i-th molecule. If the dielectric is isotropic and E is not too large, then
slide number 8
Description of the slide:
A plate of a homogeneous dielectric that fills the space between two infinite parallel oppositely charged planes and is, therefore, in a uniform external electric field E0. Under the action of the field, the dielectric is polarized, i.e., charges are displaced. Positives are shifted to the right across the field, and negatives are shifted to the left against the field. On the right side of the dielectric facing the negative plane, there will be an excess of positive charge with a surface density of +σ, on the left side, the side of the positive plate, there will be an excess of negative charge with a surface density of -σ. These uncompensated charges, which appear as a result of the polarization of the dielectric, are called bound.
slide number 9
Description of the slide:
Due to the appearance of bound charges on the dielectric, some of the lines of tension will not pass through the dielectric. They will end (or start) on connected charges. Accordingly, the electric field strength inside the dielectric will be less than E0. The appearance of bound charges leads to the appearance of an additional electric field E "(the field created by the bound charges). This field is directed against the external field E0 (the field created by free charges) and weakens it. The resulting field inside the dielectric The field created by two infinite charged planes; therefore E \u003d E0 - E "
slide number 10
Description of the slide:
Let us determine the surface density of bound charges σ'. the total dipole moment of the dielectric plate pV = PV = PSd, where S is the area of the plate face, d is its thickness. Thus. pV \u003d PSd \u003d σ "Sd and therefore σ" \u003d P, i.e., the surface density σ "of bound charges is equal to the polarization P. On the other hand, the total dipole moment, by definition From the definition of polarization, we obtain that it is equal to the product of the bound charge of each face . (Q" = σ"S) by the distance d between them, d = l
slide number 11
Description of the slide:
Substituting into the expressions σ "= P and we get from where the strength of the resulting field inside the dielectric is equal to. The dimensionless quantity is called the dielectric constant of the medium.
slide number 12
Description of the slide:
slide number 13
Description of the slide:
The vector of the electrostatic field depends on the properties of the medium, and when passing through the boundary of the dielectric, it undergoes an abrupt change. Therefore, in addition to the vector E, the electric displacement vector is used to characterize the electrostatic field, which does not undergo a discontinuity at the boundary of two media. where ε0 is the electrical constant; ε is the dielectric constant of the medium. Electrical displacement, making it difficult to calculate fields. For an isotropic medium, the electric displacement vector
slide number 14
Description of the slide:
slide number 15
Description of the slide:
slide number 16
Description of the slide:
Bound charges appear in a dielectric in the presence of an external electrostatic field. The external field is created by a system of free electric charges. In a dielectric, there is an electrostatic field of free charges and, additionally, an electrostatic field of bound charges. The resulting field in the dielectric is described by the strength vector E, and therefore it depends on the properties of the dielectric. The vector D describes the electrostatic field created by free charges. Bound charges that arise in a dielectric can cause a redistribution of free charges that create a field. The vector D characterizes the electrostatic field created by free charges, but with such a distribution in space, which is available in the presence of a dielectric. The field D, like the field E, is depicted using the lines of force of the electric displacement vector, the direction and density of which are determined in exactly the same way as for the lines of the field strength vector. The lines of the vector E can begin and end on any charges - free and bound, while the lines of the vector D - only on free charges. Through the field regions where the bound charges are located, the lines of the vector D pass without interruption.
slide number 17
Description of the slide:
The number of lines of the vector D penetrating the elementary area dS, the normal n of which forms an angle α with the vector D, DdScosα = DndS, where Dn is the projection of the vector D onto the normal n to the area dS. where Flux of the vector D. Gauss's theorem for the field in a dielectric Flux of the electric displacement vector through the area dS is similar to the flux of the vector E
slide number 18
Description of the slide:
The flow of the vector D - depends not only on the configuration of the field D, but also on the choice of direction n. The unit of the flow of the vector D in SI is the coulomb (C). 1 C is equal to the electrical displacement flux associated with the total free charge of 1 C. For an arbitrary closed surface S, the flow of vector D through this surface
slide number 19
Description of the slide:
Gauss' theorem for an electrostatic field in a dielectric The flow of the displacement vector of an electrostatic field in a dielectric through an arbitrary closed surface is equal to the algebraic sum of the free electric charges contained within this surface. In the case of a continuous charge distribution in space with a bulk density, the Gauss theorem for an electrostatic field in a dielectric can be written as The flux of the displacement vector of the electrostatic field in the dielectric through an arbitrary closed surface is equal to the free charge contained in the volume bounded by this surface.
slide number 20
Description of the slide:
For the case of vacuum, the formula can be formally written in the form Since the sources of the field E in the medium are both free and bound charges, the Gauss theorem for the field E in the most general form can be written as where and, respectively, the algebraic sums of free and bound charges covered by a closed surface S. However, this formula is unacceptable for describing the field E in a dielectric, since it expresses the properties of the unknown field E in terms of bound charges, which, in turn, are determined by it. This once again proves the expediency of introducing the electric displacement vector.
22
Description of the slide:
slide number 23
Description of the slide:
The projection of the intensity vector parallel to the interface is called the tangential component of the vector Dividing from the left and right by we get: The tangential vector Eτ is the same on both sides of the interface (does not undergo a jump), i.e. it is continuous
To obtain conditions for the normal components of the vectors E and D, we construct a straight cylinder of negligible height, one base of which is in the first dielectric, the other in the second. The bases of ΔS are so small that within each of them the vector D is the same. According to the Gauss theorem, for a field in a dielectric, where there are no free charges, we get (the normals n and n "to the bases of the cylinder are directed oppositely). The normal component of the vector D is continuous, without undergoing a jump. Therefore
slide number 26
Description of the slide:
Replacing, according to the projection of the vector D by the projections of the vector E, multiplied by εоε, we obtain the Normal component of the vector E at the interface between two dielectrics undergoes a jump. Thus, if there are no free charges at the interface between two homogeneous isotropic dielectrics, then when this boundary is passed, the components Eτ and Dn change continuously (do not undergo a jump), and the components Ep and Dτ undergo a jump. It follows from the conditions for the component vectors E and D that the lines of these vectors experience a break (refract).
slide number 27
Description of the slide:
Ferroelectrics are crystalline dielectrics that have spontaneous (spontaneous) polarization in a certain temperature range. Polarization, in the absence of an external electric field, changes significantly under the influence of external influences such as changes in temperature, electric field, deformation. These properties were first discovered by I.V. Kurchatov and P.P. Kobeko (1930) in the study of crystals of Rochelle salt NaKS4H4O6 4H,O. She gave the name ferroelectrics to this type of crystals. Later it turned out that barium titanate, potassium dihydrogen phosphate, etc., have similar properties.
slide number 28
Description of the slide:
In the absence of an external electric field, a ferroelectric is like a mosaic of domains. Domains are regions with different directions of polarization. The arrows in the figure indicate the directions of the polarization vector. When a ferroelectric is introduced into an external field, the reorientation of the dipole moments of the domains along the field occurs. The resulting total electric field of the domains will maintain their certain orientation even after the termination of the external field. Therefore, ferroelectrics have anomalously large dielectric permittivities (for Rochelle salt, for example, sgn ~ 104). In adjacent domains, these directions are different, and, in general, the dipole moment of the dielectric is zero.
slide number 29
Description of the slide:
The properties of ferroelectrics strongly depend on temperature. Each ferroelectric is characterized by the so-called Curie point. The Curie point is the temperature characteristic of each type of ferroelectric, above which their unusual electrical properties disappear. In this case, the ferroelectric turns into a conventional polar dielectric. When the material is cooled, the ferroelectric properties are restored. As a rule, ferroelectrics have only one Curie point; the only exceptions are Rochelle's salt (-18 and +24 °C) and compounds isomorphic with it. In ferroelectrics, near the Curie point, a sharp increase in the heat capacity of the substance is also observed. The transformation of ferroelectrics into an ordinary dielectric, which occurs at the Curie point, is accompanied by a second-order phase transition.
slide number 30
Description of the slide:
In ferroelectrics, the phenomenon of dielectric hysteresis (delay) is observed, which consists in the fact that the ferroelectric has different polarized values at the same electric field strength (depending on the value of the preliminary polarization of the sample). With an increase in the strength E of the external electric field, the polarization P increases, reaching saturation (curve l). The decrease in P with decreasing E occurs along curve 2, and at E = 0, the ferroelectric retains the residual polarization Poc, i.e., the ferroelectric remains polarized in the absence of an external electric field.
slide number 31
Description of the slide:
To destroy the residual polarization, it is necessary to apply an electric field in the opposite direction (-E.). The value of Es is called the coercive force (from the Latin coercitio - holding). If E is further changed, then P changes along curve 3 of the hysteresis loop. We should also mention piezoelectrics - crystalline substances in which, when compressed or stretched in certain directions, polarization occurs even in the absence of an external electric field (direct piezoelectric effect). The reverse piezoelectric effect is also observed - the appearance of mechanical deformation under the action of an electric field. In some piezoelectrics, the positive ion lattice shifts relative to the negative ion lattice upon heating, as a result of which they become polarized even without an external electric field. Such crystals are called pyroelectrics. There are also electrets - dielectrics that retain a polarized state for a long time after the removal of an external electric field (electrical analogues of permanent magnets). These groups of substances are widely used in engineering and household appliances.
FOR EXAMPLE: air, glass, plexiglass, ebonite, mica, porcelain, dry wood and others. DIELECTRIC or insulators - (from the Greek "two" through and the English "electrician" - electric) substances in which there are no free electric charges and through which electromagnetic interactions are transmitted
The structure of the dielectric The structure of the sodium chloride molecule NaCl Na Cl An electric dipole is a combination of two point charges that are equal in magnitude and opposite in sign.
POLAR, consisting of such molecules, in which the centers of distribution of positive and negative charges do not coincide table salt, alcohols, water, etc. NON-POLE, consisting of atoms or molecules, in which the centers of distribution of positive and negative charges coincide inert gases, O 2, H 2, benzene, polyethylene, etc.
The intensity vector E 1 of the electric field created by bound charges on the surface of the dielectric is directed inside the dielectric opposite to the intensity vector E 0 of the external electric field that causes polarization. The electric field strength inside an infinite space completely filled with a dielectric turns out to be equal in absolute value to E \u003d E 0 -E 1. A piece of wood (it is also a dielectric) E 1 E 0 FIELD IN THE DIELECTRIC
