Dielectric constant of substances
Substance |
Substance |
||
Gases and water vapor |
Liquids |
||
| Nitrogen | 1,0058 | Glycerol | 43 |
| Hydrogen | 1,00026 | Liquid oxygen (at t = -192.4 o C) | 1,5 |
| Air | 1,00057 | Transformer oil | 2,2 |
| Vacuum | 1,00000 | Alcohol | 26 |
| Water vapor (at t=100 o C) | 1,006 | Ether | 4,3 |
| Helium | 1,00007 | Solids |
|
| Oxygen | 1,00055 | Diamond | 5,7 |
| Carbon dioxide | 1,00099 | Waxed paper | 2,2 |
Liquids |
Dry wood | 2,2-3,7 | |
| Liquid nitrogen (at t = -198.4 o C) | 1,4 | Ice (at t = -10 o C) | 70 |
| Petrol | 1,9-2,0 | Paraffin | 1,9-2,2 |
| Water | 81 | Rubber | 3,0-6,0 |
| Hydrogen (at t= - 252.9 o C) | 1,2 | Mica | 5,7-7,2 |
| Liquid helium (at t = - 269 o C) | 1,05 | Glass | 6,0-10,0 |
| Barium titanate | 1200 | ||
| Porcelain | 4,4-6,8 | ||
| Amber | 2,8 | ||
Note. Electric constant ԑ o (dielectric constant of vacuum) equal to: ԑ o = 1\4πс 2 * 10 7 F/m ≈ 8.85 * 10 -12 F/m
Magnetic permeability of a substance
Note. Magnetic constant μ o (magnetic permeability of vacuum) is equal to: μ o = 4π * 10 -7 H/m ≈ 1.257 * 10 -6 H/m
Magnetic permeability of ferromagnets
The table shows the values of magnetic permeability for some ferromagnets (substances with μ > 1). Magnetic permeability for ferromagnetic materials (iron, cast iron, steel, nickel, etc.) is not constant. The table shows the maximum values.
1 Permalloy-68- alloy of 68% nickel and 325 iron; This alloy is used to make transformer cores.
Curie temperature
Electrical resistivity of materials
High resistance alloys
Alloy name |
Electrical resistivity µOhm m |
Alloy composition, % |
|||
Manganese |
Other elements |
||||
| Constantan | 0,50 | 54 | 45 | 1 | - |
| Kopel | 0,47 | 56,5 | 43 | 0,05 | - |
| Manganin | 0,43 | > 85 | 2-4 | 12 | - |
| Nickel silver | 0,3 | 65 | 15 | - | 20 Zn |
| Nikelin | 0,4 | 68,5 | 30 | 1,5 | - |
| Nichrome | 1,1 | - | > 60 | < 4 | 30 < Cr ост. Fe |
| Fechral | 1,3 | - | - | - | 12-15 Cr 3-4 Al 80< Fe |
Temperature coefficients of electrical resistance of conductors
Conductor |
Conductor |
||
| Aluminum | Nickel | ||
| Tungsten | Nichrome | ||
| Iron | Tin | ||
| Gold | Platinum | ||
| Constantan | Mercury | ||
| Brass | Lead | ||
| Magnesium | Silver | ||
| Manganin | Steel | ||
| Copper | Fechral | ||
| Nickel silver | Zinc | ||
| Nikelin | Cast iron |
Superconductivity of conductors
- Notes
- Superconductivity found in more than 25 metal elements and in a large number of alloys and compounds.
- Until recently, the superconductor with the highest transition temperature to the superconducting state -23.2 K (-250.0 o C) - was niobium germanide (Nb 3 Ge). At the end of 1986, a superconductor with a transition temperature of ≈ 30 K (≈ -243 o C) was obtained. The synthesis of new high-temperature superconductors is reported: ceramics (manufactured by sintering oxides of barium, copper and lanthanum) with a transition temperature of ≈ 90-120 K.
Electrical resistivity of some semiconductors and dielectrics
| Substance | GlassTemperature, o C | Resistivity | |
| Ohm m | Ohm mm2/m | ||
Semiconductors |
|||
| Indium antimonide | 17 | 5.8 x 10 -5 | 58 |
| Bor | 27 | 1.7 x 10 4 | 1.7 x 10 10 |
| Germanium | 27 | 0,47 | 4.7 x 10 5 |
| Silicon | 27 | 2.3 x 10 3 | 2.3 x 10 9 |
| Lead(II) selenide (PbSe) | 20 | 9.1 x 10 -6 | 9,1 |
| Lead(II) sulfide (PbS) | 20 | 1.7 x 10 -5 | 0,17 |
Dielectrics |
|||
| Distilled water | 20 | 10 3 -10 4 | 10 9 -10 10 |
| Air | 0 | 10 15 -10 18 | 10 21 -10 24 |
| Beeswax | 20 | 10 13 | 10 19 |
| Dry wood | 20 | 10 9 -10 10 | 10 15 -10 16 |
| Quartz | 230 | 10 9 | 10 15 |
| Transformer oil | 20 | 10 11 -10 13 | 10 16 -10 19 |
| Paraffin | 20 | 10 14 | 10 20 |
| Rubber | 20 | 10 11 -10 12 | 10 17 -10 18 |
| Mica | 20 | 10 11 -10 15 | 10 17 -10 21 |
| Glass | 20 | 10 9 -10 13 | 10 15 -10 19 |
Electrical properties of plastics
| Name of plastic | The dielectric constant | |
| Getinax | 4,5-8,0 | 10 9 -10 12 |
| Capron | 3,6-5,0 | 10 10 -10 11 |
| Lavsan | 3,0-3,5 | 10 14 -10 16 |
| Organic glass | 3,5-3,9 | 10 11 -10 13 |
| Styrofoam | 1,0-1,3 | ≈ 10 11 |
| Polystyrene | 2,4-2,6 | 10 13 -10 15 |
| Polyvinyl chloride | 3,2-4,0 | 10 10 -10 12 |
| Polyethylene | 2,2-2,4 | ≈ 10 15 |
| Fiberglass | 4,0-5,5 | 10 11 -10 12 |
| Textolite | 6,0-8,0 | 10 7 -10 19 |
| Celluloid | 4,1 | 10 9 |
| Ebonite | 2,7-3,5 | 10 12 -10 14 |
Specific electrical resistance of electrolytes (at t=18 o C and 10% solution concentration)
Rushing. The resistivity of electrolytes depends on temperature and concentration, i.e. from the ratio of the mass of dissolved acid, alkali or salt to the mass of dissolving water. At the specified concentration of solutions, an increase in temperature by 1 o C reduces the resistivity of a solution taken at 18 o C by 0.012 for sodium hydroxide, by 0.022 for copper sulfate, by 0.021 for sodium chloride, by 0.013 for sulfuric acid and by 0.003 - for 100 percent sulfuric acid.
Specific electrical resistance of liquids
Liquid |
Electrical resistivity, Ohm m |
Liquid |
Electrical resistivity, Ohm m |
| Acetone | 8.3 x 10 4 | Molten Salts: | |
| Distilled water | 10 3 - 10 4 | potassium hydroxide (KOH; at t = 450 o C) | 3.6 x 10 -3 |
| Sea water | 0,3 | sodium hydroxide (NaOH; at t = 320 o C) | 4.8 x 10 -3 |
| River water | 10-100 | sodium chloride (NaCl; at t = 900 o C) | 2.6 x 10 -3 |
| Air is liquid (at t = -196 o C) | 10 16 | soda (Na 2 CO 3 x10H 2 O; at t = 900 o C) | 4.5 x 10 -3 |
| Glycerol | 1.6 x 10 5 | Alcohol | 1.5 x 10 5 |
| Kerosene | 10 10 | ||
| Melted naphthalene (at (at t = 82 o C) | 2.5 x 10 7 | ||
The magnetic field of the coil is determined by the current and the strength of this field, and the field induction. Those. The field induction in a vacuum is proportional to the magnitude of the current. If a magnetic field is created in a certain environment or substance, then the field affects the substance, and it, in turn, changes the magnetic field in a certain way.
A substance located in an external magnetic field is magnetized and an additional internal magnetic field appears in it. It is associated with the movement of electrons along intra-atomic orbits, as well as around their own axis. The movement of electrons and atomic nuclei can be considered as elementary circular currents.
The magnetic properties of an elementary circular current are characterized by a magnetic moment.
In the absence of an external magnetic field, the elementary currents inside the substance are oriented randomly (chaotically) and, therefore, the total or total magnetic moment is zero and the magnetic field of elementary internal currents is not detected in the surrounding space.
The influence of an external magnetic field on elementary currents in matter is that the orientation of the axes of rotation of charged particles changes so that their magnetic moments are directed in one direction. (towards the external magnetic field). The intensity and nature of magnetization of different substances in the same external magnetic field differ significantly. The quantity characterizing the properties of the medium and the influence of the medium on the magnetic field density is called absolute magnetic permeability or magnetic permeability of the medium (μ With ) . This is the relation = . Measured [ μ With ]=Gn/m.
The absolute magnetic permeability of a vacuum is called the magnetic constant μ O =4π 10 -7 H/m.
The ratio of absolute magnetic permeability to magnetic constant is called relative magnetic permeabilityμ c /μ 0 =μ. Those. relative magnetic permeability is a value that shows how many times the absolute magnetic permeability of the medium is greater or less than the absolute permeability of vacuum. μ is a dimensionless quantity that varies over a wide range. This value forms the basis for dividing all materials and media into three groups.
Diamagnets . These substances have μ< 1. К ним относятся - медь, серебро, цинк, ртуть, свинец, сера, хлор, вода и др. Например, у меди μ Cu = 0,999995. Эти вещества слабо взаимодействуют с магнитом.
Paramagnets . These substances have μ > 1. These include aluminum, magnesium, tin, platinum, manganese, oxygen, air, etc. Air = 1.0000031. . These substances, like diamagnetic materials, interact weakly with a magnet.
For technical calculations, μ of diamagnetic and paramagnetic bodies is taken equal to unity.
Ferromagnets . This is a special group of substances that play a huge role in electrical engineering. These substances have μ >> 1. These include iron, steel, cast iron, nickel, cobalt, gadolinium and metal alloys. These substances are strongly attracted to a magnet. For these substances, μ = 600-10,000. For some alloys, μ reaches record values of up to 100,000. It should be noted that μ for ferromagnetic materials is not constant and depends on the magnetic field strength, type of material and temperature.
The large value of µ in ferromagnets is explained by the fact that they contain regions of spontaneous magnetization (domains), within which the elementary magnetic moments are directed in the same way. When folded, they form common magnetic moments of the domains.
In the absence of a magnetic field, the magnetic moments of the domains are randomly oriented and the total magnetic moment of the body or substance is zero. Under the influence of an external field, the magnetic moments of the domains are oriented in one direction and form a common magnetic moment of the body, directed in the same direction as the external magnetic field.
This important feature is used in practice by using ferromagnetic cores in coils, which makes it possible to sharply increase magnetic induction and magnetic flux at the same values of currents and number of turns or, in other words, to concentrate the magnetic field in a relatively small volume.
Magnetic permeability is different for different media and depends on its properties, therefore it is customary to talk about the magnetic permeability of a specific medium (meaning its composition, state, temperature, etc.).
In the case of a homogeneous isotropic medium, magnetic permeability μ:
μ = V/(μ o N),
In anisotropic crystals, magnetic permeability is a tensor.
Most substances are divided into three classes according to their magnetic permeability:
- diamagnetic materials ( μ < 1 ),
- paramagnets ( μ > 1 )
- ferromagnets (possessing more pronounced magnetic properties, such as iron).
The magnetic permeability of superconductors is zero.
The absolute magnetic permeability of air is approximately equal to the magnetic permeability of vacuum and in technical calculations is taken equal to 4π 10 -7 Gn/m
μ = 1 + χ (in SI units);
μ = 1 + 4πχ (in GHS units).
Magnetic permeability of physical vacuum μ =1, since χ=0.
Magnetic permeability shows how many times the absolute magnetic permeability of a given material is greater than the magnetic constant, i.e., how many times the magnetic field of macrocurrents N is enhanced by the field of microcurrents in the environment. The magnetic permeability of air and most substances, with the exception of ferromagnetic materials, is close to unity.
Several types of magnetic permeability are used in technology, depending on the specific applications of the magnetic material. Relative magnetic permeability shows how many times in a given medium the force of interaction between wires with current changes compared to vacuum. Numerically equal to the ratio of absolute magnetic permeability to magnetic constant. Absolute magnetic permeability is equal to the product of magnetic permeability and magnetic constant.
Diamagnets have χμχ>0 and μ > 1. Depending on whether μ of ferromagnets is measured in a static or alternating magnetic field, it is called static or dynamic magnetic permeability, respectively.
The magnetic permeability of ferromagnets depends in a complex way on N . From the magnetization curve of a ferromagnet, one can construct the dependence of magnetic permeability on N.
Magnetic permeability, determined by the formula:
μ = V/(μ o N),
called static magnetic permeability.
It is proportional to the tangent of the secant angle drawn from the origin through the corresponding point on the main magnetization curve. The limiting value of magnetic permeability μ n when the magnetic field strength tends to zero is called the initial magnetic permeability. This characteristic is of utmost importance in the technical use of many magnetic materials. It is determined experimentally in weak magnetic fields with a strength of the order of 0.1 A/m.