What is the resistivity of a substance? To answer this question in simple terms, one needs to recall a physics course and present the physical embodiment of this definition. An electric current is passed through the substance, and it, in turn, prevents the passage of current with some force.
- 1 The concept of resistivity of a substance
- 2 Copper use
- 3 Metal resistance table
4 Copper. Its characteristics and properties
- 4.1 Description of the substance and properties
- 4.2 Copper grades
- 4.3 Effect of impurities on the properties of copper
The concept of resistivity of a substance
It is this quantity, which shows how strongly the substance impedes the current and is the specific resistance (the Latin letter “ro”). In the international system of units resistance expressed in ohmsmultiplied by the meter. The formula for the calculation is: "The resistance is multiplied by the cross-sectional area and divided by the length of the conductor."
The question arises: “Why is another resistance being used when finding the specific resistance?”. The answer is simple, there are two different values - resistivity and resistance. The second shows how the substance is able to prevent the passage of current through it, and the first shows almost the same only it is no longer a matter of a substance in a general sense, but a conductor with a specific length and cross-sectional area, which are made of this substances.
The reciprocal, which characterizes the ability of a substance to pass electricity, is called the specific electrical conductivity and the formula by which the resistivity is calculated is directly related to the specific conductivity.
The concept of resistivity is widely used in the calculation of the conductivity of electric current by various metals. Based on these calculations, decisions are made about the appropriateness of the use of a metal for manufacturing electrical conductors that are used in construction, instrument making and other areas.
Metal resistance table
Are there certain tables? in which the available data on the transmission and resistance of metals are summarized, as a rule, these tables are calculated for certain conditions.
In particular, it is widely known metal single crystal resistance table at a temperature of twenty degrees Celsius, as well as the table of resistance of metals and alloys.
These tables are used to calculate various data in the so-called ideal conditions, in order to calculate values for specific purposes, you need to use formulas.
Copper. Its characteristics and properties
Description of the substance and properties
Copper is a metal that was discovered by mankind for a long time and has also been used for various technical purposes for a long time. Copper is a very ductile and ductile metal with high electrical conductivity, which makes it very popular for the manufacture of various wires and conductors.
Physical properties of copper:
- melting temperature - 1084 degrees Celsius;
- boiling point - 2560 degrees Celsius;
- density at 20 degrees - 8890 kilograms divided by cubic meter;
- specific heat at constant pressure and temperature of 20 degrees - 385 kJ / J * kg
- electrical resistivity - 0,01724;
This metal can be divided into several groups or brands, each of which has its own properties and its application in industry:
- Mark M00, M0, M1 - are excellent for the production of cables and conductors, when it is melted, oversaturation with oxygen is eliminated.
- The M2 and M3 grades are cheap options that are designed for small rolled products and satisfy most technical and industrial tasks on a small scale.
- M1, M1f, M1p, M2p, M3r grades are expensive copper brands that are manufactured for a specific consumer with specific requirements and demands.
Between brands differ in several parameters:
- type of delivery;
- oxygen saturation;
- difference in resistance;
- the presence of impurities;
- degree of thermal conductivity;
Effect of impurities on the properties of copper
Impurities can affect the mechanical, technical and operational properties of products.
- Mechanical properties. Substances such as iron, bismuth, lead or oxygen affect the ductility of copper. Some poorly soluble impurities affect the preservation of the structure of a substance with increasing temperature. For example, lead or bismuth makes copper very fragile, but adding at least a small amount of silver (five hundredths of a percent) significantly increases the fusibility of copper, that is, even at high temperatures, its crystal lattice remains unchanged, while there is no rubbing of heat or electrical conductivity.
- Technical properties. These include pressure treatment at different temperatures and the alloying (welding) of the substance. In the presence of poorly soluble impurities in copper, zones of particular brittleness appear at high temperatures; this makes pressure treatment is very difficult, however, in grades M1 and M2, the desired plasticity is achieved due to the low content impurities. If we talk about pressure at low temperatures, then this technology is used in the manufacture of wire rod (wire) and for different grades the ability to extract is also different.
- Performance properties. Under standard operating conditions, different brands behave quite the same, but due to the content of hydrogen and oxygen in different brands, conditions are applied when the temperature rises. In particular, oxygen begins to adversely affect copper when the ambient temperature rises, and hydrogen when the substance is heated to two hundred degrees.
In conclusion, it should be emphasized that copper is a unique metal with unique properties. It is used in the automotive industry, the manufacture of elements for the electrical industry, electrical appliances, consumer goods, watches, computers and much more. With its low resistivity, this metal is an excellent material for the manufacture of conductors and other electrical appliances. With this property, copper overtakes only silver, but because of its higher cost, it has not found the same application in the electrical industry.