Presentation on the topic "conductors and dielectrics." Presentation on the topic “conductors and dielectrics” What substances are called dielectrics

CONDUCTORS AND DIELECTRICS IN AN ELECTRIC FIELD

Basic course

• Conductors are substances that contain free electrical charges that can move under the influence of an arbitrarily weak electric field.

CONDUCTORS

IONIZED

GASES

METALS

ELECTROLYTES

Electrostatic protection– a phenomenon according to which it is possible to shield an electric field by “hiding” from it inside a closed shell made of electrically conductive material (for example, metal).

Electrostatic protection.

The phenomenon was discovered by Michael Faraday in 1836. He noticed that an external electric field could not get inside a grounded metal cage. Operating principle Faraday cages lies in the fact that under the influence of an external electric field, free electrons located in the metal begin to move and create a charge on the surface of the cell that completely compensates for this external field.

Dielectrics (or insulators) are substances that conduct electricity relatively poorly (compared to conductors).

• In dielectrics, all electrons are bound, i.e., they belong to individual atoms, and the electric field does not tear them off, but only slightly shifts them, i.e., polarizes them. Therefore, an electric field can exist inside the dielectric; the dielectric has a certain influence on the electric field

Dielectrics are divided into polar And non-polar .

Polar dielectrics

consist of molecules in which the centers of distribution of positive and negative charges do not coincide. Such molecules can be represented as two identical in modulus opposite point molecules charges , located at some distance from each other, called dipole .

Non-polar dielectrics

consist of atoms and molecules in which the centers of distribution of positive and negative charges coincide.

Polarization of polar dielectrics.

• Placing a polar dielectric in an electrostatic field (for example, between two charged plates) leads to a reversal and displacement of previously chaotically oriented dipoles along the field.

The reversal occurs under the influence of a pair of forces applied from the field to two dipole charges.

The displacement of dipoles is called polarization. However, due to thermal motion, only partial polarization occurs. Inside the dielectric, the positive and negative charges of the dipoles compensate each other, and on the surface of the dielectric a bound charge appears: negative on the side of the positively charged plate, and vice versa.

Polarization of non-polar dielectrics

A non-polar dielectric in an electric field is also polarized. Under the influence of an electric field, positive and negative charges in a molecule are displaced in opposite directions, so that the centers of charge distribution are displaced, like those of polar molecules. The axis of the field-induced dipole is oriented along the field. Bound charges appear on the dielectric surfaces adjacent to the charged plates.

A polarized dielectric itself creates an electric field.

This field weakens the external electric field inside the dielectric

The degree of this attenuation depends on the properties of the dielectric.

A decrease in the strength of the electrostatic field in a substance compared to the field in a vacuum is characterized by the relative dielectric constant of the medium.

Conductors in an electric field

Dielectrics in an electric field

1. There are free electrons

1. There are no free charge carriers.

2.electrons collect on the surface of the conductor

2. In an electric field, molecules and atoms rotate so that on one side an excess positive charge appears in the dielectric, and on the other - a negative one

3. There is no electric field inside the conductor

3. The electric field inside the conductor weakens by ε times.

4. A conductor can be divided into 2 parts in an electric field, and each part will be charged with different signs.

4. A dielectric can be divided into 2 parts in an electric field, but each of them will be uncharged

Security questions

1 . What substances are called conductors?

2What electric charges are called free?

3.What particles are carriers of free charges in metals?

4.What happens in a metal placed in an electric field?

5. How the dawn communicated to him is distributed over the conductor d?

TEST QUESTIONS.

6. If a conductor in an electric field is divided into two parts, how will these parts be charged?

7.What principle is electrostatic protection based on?

8.What substances are called dielectrics?

9.What types of dielectrics are there? How are they different?

10.Explain the behavior of a dipole in an external electric field.

11. How polarization of dielectrics occurs.

12. If a dielectric placed in an electric field is divided in half, what will be the charge of each part?

13. A negatively charged cloud passes over a lightning rod. Explain, based on electronic concepts, why a charge appears at the tip of the lightning rod. What is his sign?

Conductors in an electric field Free charges - charged particles of the same sign, capable of moving under the influence of an electric field Bound charges - opposite charges included in atoms (or molecules) that cannot move under the influence of an electric field independently of each other substances conductors dielectrics semiconductors

Any medium weakens the electric field strength

The electrical characteristics of a medium are determined by the mobility of charged particles in it

Conductor: metals, solutions of salts, acids, moist air, plasma, human body

This is a body that contains a sufficient amount of free electrical charges inside that can move under the influence of an electric field.

If you introduce an uncharged conductor into an electric field, the charge carriers begin to move. They are distributed so that the electric field they create is opposite to the external field, that is, the field inside the conductor will be weakened. Charges will be redistributed until the conditions for equilibrium of charges on the conductor are met, that is:

a neutral conductor introduced into an electric field breaks the tension lines. They end at negative induced charges and begin at positive

The phenomenon of spatial separation of charges is called electrostatic induction. The self-field of the induced charges compensates for the external field inside the conductor with a high degree of accuracy.

If the conductor has an internal cavity, then the field will be absent inside the cavity. This circumstance is used when organizing the protection of equipment from electric fields.

The electrification of a conductor in an external electrostatic field by the separation of positive and negative charges already present in it in equal quantities is called the phenomenon of electrostatic induction, and the redistributed charges themselves are called induced. This phenomenon can be used to electrify uncharged conductors.

An uncharged conductor can be electrified by contact with another charged conductor.

The distribution of charges on the surface of conductors depends on their shape. The maximum charge density is observed at the points, and inside the recesses it is reduced to a minimum.

The property of electric charges to concentrate in the surface layer of a conductor has found application for obtaining significant potential differences by electrostatic method. In Fig. a diagram of an electrostatic generator used to accelerate elementary particles is shown.

A spherical conductor 1 of large diameter is located on an insulating column 2. A closed dielectric tape 3 moves inside the column, driving drums 4. From a high-voltage generator, an eclectic charge is transmitted through a system of pointed conductors 5 to the tape, on the back side of the tape there is grounding plate 6. Charges from the tape are removed by a system of points 7 and flow onto the conducting sphere. The maximum charge that can accumulate on a sphere is determined by leakage from the surface of the spherical conductor. In practice, with generators of a similar design, with a sphere diameter of 10–15 m, it is possible to obtain a potential difference of the order of 3–5 million volts. To increase the charge of the sphere, the entire structure is sometimes placed in a box filled with compressed gas, which reduces the intensity of ionization.

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On the surface of the sphere, cones cut out small spherical areas that 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. From the similarity it follows that the areas of the bases are related as the squares of the distances from point A to the sites and, respectively. Thus,

Equipotential surfaces An approximate course of equipotential surfaces for a certain moment of cardiac excitation 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 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 Titanium barium 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. A textbook for 10th grade schools and classes with in-depth study of physics." A. A. Pinsky “Physics. A textbook for 10th grade schools and classes with in-depth study of physics." G. Ya. Myakishev “Physics. Electrodynamics classes". G. Ya. Myakishev “Physics. Electrodynamics classes". Magazine "Kvant". Magazine "Kvant".

Conductors and dielectrics

Electric field in matter. Any environment weakens the electric field strength. The electrical characteristics of a medium are determined by the mobility of charged particles in it. Substances, conductors, semiconductors, dielectrics. Substances. Free charges are charged particles of the same sign that can move under the influence of an electric field. Bound charges are unlike charges that cannot move under the influence of an electric field independently of each other. Conductors. Conductors are substances in which free charges can move throughout the volume. Conductors - metals, solutions of salts, acids, moist air, plasma, human body. - Explorer.ppt

Conductors in an electric field

Conductors in an electric field. There is no electric field in other conductors either. Let's consider the electric field inside a metal conductor...... Dielectrics. In non-polar dielectrics, the center of the positive and negative charge coincides. In an electric field, any dielectric becomes polar. Dipole. Polarization of dielectrics. - Conductors in an electric field.ppt

Conductors in an electrostatic field

Conductors and dielectrics in an electrostatic field. Conductors in an electrostatic field Dielectrics in an electrostatic field. - Metals; liquid solutions and melts of electrolytes; plasma. Conductors include: Conductors in an electrostatic field. Evnesh. The internal field will weaken the external one. Evn. There is no field inside a conductor placed in an electrostatic field. Electrostatic properties of homogeneous metal conductors. Dielectrics. Polar. Non-polar. Dielectrics include air, glass, hard rubber, mica, porcelain, and dry wood. Dielectrics in an electrostatic field. - Conductors in an electrostatic field.ppt

Conductors and dielectrics

Electric field. Conductors and dielectrics in an electrostatic field. Conductors and dielectrics. Substances by conductivity. Last electron. Structure of metals. Metal conductor. Metal conductor in an electrostatic field. Dielectric structure. The structure of a polar dielectric. Dielectric in an electric field. Dielectric constant of the medium. Coulomb's law. Microwave. Microwave. How microwaves heat food. Power. - Conductors and dielectrics.ppt

Conductors in an electric field; dielectrics in an electric field

Topic: “Conductors and dielectrics in an electric field.” Conductors. Charge inside a conductor. According to the principle of field superposition, the tension inside the conductor is zero. Conducting sphere. Let's take an arbitrary point A. The charges of the areas are equal. Electrostatic induction. Equipotential surfaces. The most famous electric fish are. Electric ramp. Electric eel. Dielectrics. Dielectrics are materials that have no free electrical charges. There are three types of dielectrics: polar, non-polar and ferroelectrics. - Conductors in an electric field, dielectrics in an electric field.ppt

Electric field in dielectrics

Dielectrics do not conduct electric current under normal conditions. The term "dielectrics" was introduced by Faraday. A dielectric, like any substance, consists of atoms and molecules. Dielectric molecules are electrically neutral. Polarization. Field strength in a dielectric. Under the influence of the field, the dielectric is polarized. The resulting field inside the dielectric. Field. Electrical bias. The external field is created by a system of free electric charges. Gauss's theorem for a field in a dielectric. Gauss's theorem for the electrostatic field in a dielectric. The properties of ferroelectrics strongly depend on temperature. - Dielectric.ppt

Polarization of dielectrics

Polarization of dielectrics. Relative dielectric constant. Polarization vector. Mechanisms of polarization. Spontaneous polarization. Migration polarization. Types of elastic polarization. Ionic elastic polarization. Dipole elastic polarization. Types of thermal polarization. Dipole thermal polarization. Electronic thermal polarization. Permittivity. Ferroelectrics. Piezoelectrics. Piezoelectric effects are observed only in crystals that do not have a center of symmetry. Pyroelectrics. Pyroelectrics exhibit spontaneous polarization along the polar axis. Photopolarization. -

Conductors and dielectrics in an electrostatic field

Mezhetsky Artyom

Completed:

Municipal educational institution

"Secondary school No. 30 of the city of Belovo"

Head: Popova Irina Aleksandrovna

Belovo 2011

• 1. Conductors and dielectrics.
• 2. Conductors in an electrostatic field.
• 3. Dielectrics in an electrostatic field.
Two types of dielectrics.
• 4.Dielectric constant.

Structure of metals

Metal conductor in an electrostatic field

Evn.= Evn.

Metal conductor in an electrostatic field

E external = E internal

There is no electric field inside the conductor.

The entire static charge of a conductor is concentrated on its surface.

Types of dielectrics Polar Consists of molecules whose centers of distribution of positive and negative charges do not coincide; table salt, alcohols, water, etc. Nonpolar Consists of molecules whose centers of distribution of positive and negative charges coincide. inert gases, O2, H2, benzene, polyethylene, etc. The structure of a polar dielectric

Dielectric in an electric field

E internal< Е внеш.

DIELECTRIC WEAKENS THE EXTERNAL ELECTRIC FIELD

Electric field strength in vacuum

Electric field strength in a dielectric

Dielectric constant of the medium

• Coulomb's Law:
• Electric field strength created by a point charge:

Problem Solving a problem Solving problems Solving problems Test

No. 1: A positively charged body is brought to three contacting plates A, B, C. Plates B, C are a conductor, and A is a dielectric. What charges will be on the plates after plate B is completely pulled out?

Answer options

No. 2: Charged metal ball in series

immersed in two dielectric liquids (1< 2).

Which of the following graphs

most accurately reflects the dependence

field potential versus distance,

measured from the center of the ball?

#4: A positive charge was placed in the center of a thick-walled, uncharged metal sphere. Which of the following figures corresponds to the distribution pattern of the electrostatic field lines?

No. 5: Which of the following figures corresponds to the distribution of field lines for a positive charge and a grounded metal plane?

Literature used

• Kasyanov, V.A. Physics, 10th grade [Text]: textbook for secondary schools / V.A. Kasyanov. – LLC “Drofa”, 2004. – 116 p.
• Kabardin O.F., Orlov V.A., Evenchik E.E., Shamash S.Ya., Pinsky A.A., Kabardina S.I., Dik Yu.I., Nikiforov G.G., Shefer N. .AND. "Physics. 10th grade”, “Enlightenment”, 2007