When they say that copper is heaviermetal than aluminum, then compare their density. Similarly, when it is said that copper is a better conductor than aluminum, they compare their resistivity (ρ), whose value does not depend on the size or shape of a particular sample-only on the material itself.
Resistance is a measure of resistanceelectrical conductivity for a given material size. Its opposite is electrical conductivity. Metals are good electrical conductors (high conductivity and low ρ value), while nonmetals are mainly poor conductors (low conductivity and high ρ value).
A more familiar thermal electricThe resistance measures how difficult it is for the material to conduct electricity. This depends on the size of the part: the resistance is higher for a longer or narrower section of material. To eliminate the size effect from the resistance, the resistivity of the wire is used - this is a material property that does not depend on the size. For most materials, the resistance increases with temperature. Exceptions are semiconductors (for example, silicon), in which it decreases with temperature.
The ease with which the material conducts heat,is measured by thermal conductivity. As a first evaluation, good electrical conductors are also good thermal conductors. The resistance is denoted by the symbol r, and its unit of measure is an ohmmeter. Resistance of pure copper is 1.7 × 10 -8 Ohm. This very small number - 0.000 000 017 Ohm indicates that the cubic meter of copper practically does not resist. The smaller the resistivity (ohmmeter or Ωm), the better the material is used in the wiring. Resistance is the reverse side of conductivity.
The magnitude of the resistance of the material is oftenIt is used for classification as a conductor, semiconductor or insulator. Solid elements are classified as insulators, semiconductors or conductors by their "static resistance" in the periodic table of elements. The resistivity in the insulator, semiconductor or conductive material is the main property that is taken into account for use in electrical engineering.
The table shows some data of ρ, σ and temperature coefficients. For metals, the resistance increases with increasing temperature. For semiconductors and many insulators, the reverse is true.
| Material | ρ (Ωm) at 20 ° C | σ (S / m) at 20 ° C | Temperature coefficient (1 / ° C) x10 ^ -3 |
| Silver | 1.59 × 10 -8 | 6.30 × 10 7 | 3,8 |
| Copper | 1.68 × 10 -8 | 5.96 × 10 7 | 3,9 |
| Gold | 2.44 × 10 -8 | 4.10 × 10 7 | 3,4 |
| Aluminum | 2.82 × 10 -8 | 3.5 × 10 7 | 3,9 |
| Tungsten | 5.60 × 10 -8 | 1.79 × 10 7 | 4.5 |
| Zinc | 5.90 × 10 -8 | 1.69 × 10 7 | 3,7 |
| Nickel | 6.99 × 10 -8 | 1.43 × 10 7 | 6 |
| Lithium | 9.28 × 10 -8 | 1.08 × 10 7 | 6 |
| Iron | 1.0 × 10 -7 | 1.00 × 10 7 | 5 |
| Platinum | 1.06 × 10 -7 | 9.43 × 10 6 | 3,9 |
| Lead | 2.2 × 10 -7 | 4.55 × 10 6 | 3,9 |
| Constantan | 4.9 × 10 -7 | 2.04 × 10 6 | 0,008 |
| Mercury | 9.8 × 10 -7 | 1.02 × 10 6 | 0.9 |
| Nichrome | 1.10 × 10 -6 | 9.09 × 10 5 | 0,4 |
| Carbon (amorphous) | 5 × 10 -4 up to 8 × 10 -4 | 1.25-2 × 10 3 | -0,5 |
For any given temperature, we can calculate the electrical resistance of the object in ohms, using the following formula.
In this formula:
The resistivity is equal to a certain number of ohmmeters. In spite of the fact that the unit ρ in the SI system, as a rule, is an ohmmeter, sometimes one uses the dimension of ohms per centimeter.
The resistance of the material is determined from the magnitude of the electric field along it, which gives a definite current density.
ρ = E / J, where:
How to determine the resistivity?Many resistors and conductors have a uniform cross-section with a uniform current flow. Therefore, there is a more specific but more widely used equation.
ρ = R * A / J, where:
The electrical resistivity of the material is also known asspecific electrical resistance. This is an indication of how much the material resists the flow of electric current. It can be determined by dividing the resistance per unit length and per unit cross-sectional area, for a particular material at a given temperature.
This means that a low ρ indicates material,which easily allows the movement of electrons. Conversely, a material with a high ρ will have a high resistance and impede the flow of electrons. Elements such as copper and aluminum are known for their low level of ρ. Silver and, in particular, gold have a very low value of ρ, but for obvious reasons their use is limited.
Materials are placed in different categories depending on their indicator ρ. A summary is given in the table below.
The level of conductivity of semiconductors depends onlevel of doping. Without alloying, they look almost like insulators, which is the same for electrolytes. The level ρ of materials varies widely.
| Equipment categories and type of materials | The resistivity region of the most common materials as a function of ρ |
| Electrolytes | Variable |
| Insulators | ~ 10 ^ 16 |
| Metals | ~ 10 ^ -8 |
| Semiconductors | Variable |
| Superconductors | 0 |
In most cases, the resistance increaseswith temperature. As a result, there is a need to understand the temperature dependence of the resistance. The reason for the temperature coefficient of resistance in the conductor can be justified intuitively. The resistance of the material is dependent on a number of phenomena. One of them is the number of collisions that occur between charge carriers and atoms in the material. The resistivity of the conductor will increase with increasing temperature, as the number of collisions increases.
This may not always be the case, becausetemperature increase, additional charge carriers are released, which will lead to a decrease in the resistivity of materials. This effect is often observed in semiconductor materials.
When considering the temperature dependenceit is usually assumed that the temperature coefficient of resistance follows a linear law. This concerns the temperature in the room and for metals and many other materials. However, it was found that the effects of resistance arising from the number of collisions are not always constant, especially at very low temperatures (the phenomenon of superconductivity).
The conductor resistance at any given temperature can be calculated from the value of the temperature and its temperature coefficient of resistance.
R = Rref * (1 + α (T-Tref)), where:
Temperature coefficient of resistance, usually standardized at a temperature of 20 ° C. Accordingly, an equation commonly used in a practical sense:
R = R20 * (1 + α20 (T-T20)), where:
The resistance table given below containsmany of the substances widely used in electrical engineering, including copper, aluminum, gold and silver. These properties are especially important because it is determined whether the substance can be used to fabricate a wide range of electrical and electronic components from wires to more complex devices such as resistors, potentiometers and many others.
| Resistivity table for various materials at outdoor temperatures of 20 ° C | |
| Materials | Resistance of OM at a temperature of 20 ° C |
| Aluminum | 2.8 x 10 -8 |
| Antimony | 3.9 × 10 -7 |
| Bismuth | 1.3 x 10 -6 |
| Brass | ~ 0.6 - 0.9 × 10 -7 |
| Cadmium | 6 x 10 -8 |
| Cobalt | 5.6 × 10 -8 |
| Copper | 1.7 × 10 -8 |
| Gold | 2.4 x 10 -8 |
| Carbon (graphite) | 1 x 10 -5 |
| Germanium | 4.6 x 10 -1 |
| Iron | 1.0 x 10 -7 |
| Lead | 1.9 × 10 -7 |
| Nichrome | 1.1 × 10 -6 |
| Nickel | 7 x 10 -8 |
| Palladium | 1.0 x 10 -7 |
| Platinum | 0.98 × 10 -7 |
| Quartz | 7 x 10 17 |
| Silicon | 6.4 × 10 2 |
| Silver | 1.6 × 10 -8 |
| Tantalum | 1.3 x 10 -7 |
| Tungsten | 4.9 x 10 -8 |
| Zinc | 5.5 x 10 -8 |
Conductors consist of materials that areconduct an electric current. Non-magnetic metals are usually considered ideal conductors of electricity. In the wire and cable industry, various metallic conductors are used, but copper and aluminum are the most common. Conductors have different properties, such as conductivity, tensile strength, weight and environmental impact.
The conductor resistance of copper is muchmore often used in the production of cables than aluminum. Almost all electronic cables are made of copper, like other devices and equipment that use high conductivity of copper. Copper conductors are also widely used in power distribution and production systems, and in the automotive industry. To save weight and costs, the electricity transmission enterprises use aluminum in overhead power lines.
Aluminum is used in industries where it is importantlightness, such as aircraft construction, is expected to increase in the future in the automotive industry. For more powerful cables, copper-coated aluminum wire is used to use the resistivity of copper, resulting in significant weight savings of the structure from lightweight aluminum.
Copper is one of the oldest known materials.Its plasticity and electrical conductivity were used by early experimenters with electricity, such as Ben Franklin and Michael Faraday. The low ρ of copper materials led to the fact that it was adopted as the main conductors used in inventions, such as telegraph, telephone and electric motor. Copper is the most common conductive metal. In 1913, an international standard for copper calcination (IACS) was adopted to compare the conductivity of other metals with copper.
According to this standard, commercially pureAnnealed copper has a conductivity of 100% IACS. The resistivity of materials is compared with the standard. Commercially pure copper produced today may have higher IACS conductivity values, as the processing technology has significantly stepped forward over time. In addition to the excellent conductivity of copper, the metal has high tensile strength, thermal conductivity and thermal expansion. Annealed copper wire used for electrical purposes meets all the requirements of the standard.
Despite the fact that copper has a long history inas a material for the production of electricity, aluminum has certain advantages that make it attractive for a particular application, and its current resistivity makes it possible to expand the field of its use many times. Aluminum has 61% conductivity of copper and only 30% of the weight of copper. This means that a wire made of aluminum weighs half as much as a copper wire with the same electrical resistance.
Aluminum, as a rule, is cheaper in comparison withcopper dwelling. Aluminum conductors consist of different alloys, have a minimum aluminum content of 99.5%. In the 1960s and 1970s, due to the high price of copper, this class of aluminum became widely used for household electrical wiring.
Due to poor quality of workmanship underconnections and physical differences between aluminum and copper, devices and wires made on the basis of their connections in places of contacts copper-aluminum became fire hazardous. To counteract the negative process, aluminum alloys with creep and elongation properties more similar to copper were developed. These alloys are used for the manufacture of stranded aluminum wires, the specific current resistance of which is acceptable for mass use, meeting the safety requirements for electrical networks.
If aluminum is used in places where copper was previously used to maintain equal network performance, you have to use an aluminum wire that is twice the size of the copper wire.
Many of the materials found in the tableresistivity, are widely used in electronics. Aluminum and especially copper are used because of their low resistance level. Most of the wires and cables used today for electrical connections are made of copper, because it provides a low level of ρ, and have an affordable price. Good conductivity of gold, despite the price, is also used in some particularly accurate instruments.
Often gold plating is found onhigh-quality low-voltage connections, where the task is to provide the smallest contact resistance. Silver is not widely used in industrial electrical engineering, as it is rapidly oxidized, and this leads to a large contact resistance. In some cases, the oxide can act as a rectifier. Tantalum resistance is used in capacitors, nickel and palladium are used in end connections for many surface mount components. Quartz finds its main application as a piezoelectric resonant element. Quartz crystals are used as frequency elements in many generators, where its high value makes it possible to create reliable frequency contours.
