Specific resistance of copper. The physics of the process

Often in the electrotechnical literature there is a notion of " electrical resistivity of copper". And involuntarily wondering what is it?

The concept of "resistance" for any conductor is continuously associated with an understanding of the process of flowing electric current through it. Since the speech in this article is about the resistance of copper, then its properties and the properties of metals should also be considered.

When it comes to metals, you can not help recalling that they all have a certain structure - a crystal lattice. Atoms are at the nodes of such a lattice and perform periodic oscillations with respect to them . The distances and locations of these nodes depend on the forces of interaction of atoms with each other (repulsion and attraction), and are different for different metals. And around the atoms in their orbits the electrons rotate. They are also in balance in the orbit. Only this force of attraction to the atom and centrifugal. Did you picture yourself? You can call it, in a way, static.

And now add the dynamics. An electric field starts acting on a piece of copper. What happens inside the conductor? Electrons, torn by the strength of the electric field from their orbits, rush to its positive pole. Here you and the directed movement of electrons, or rather, the electric current. But on the way of their movement they stumble upon atoms in the nodes of the crystal lattice and electrons still rotating around their atoms. In this case, they lose their energy and change the direction of motion. Now the meaning of the phrase "resistance of the conductor" becomes somewhat clearer? These lattice atoms and electrons revolving around them exert resistance to the directed motion of electrons torn off by the electric field from their orbits. But the concept of resistance of a conductor can be called a general characteristic. More specifically, each conductor characterizes the resistivity. Copper as well. This characteristic is individual for each metal, since it directly depends only on the shape and dimensions of the crystal lattice and, to some extent, on the temperature. As the temperature of the conductor rises, the atoms perform a more intense oscillation at the lattice sites. And the electrons rotate around the nodes at a higher speed and in orbits of a larger radius. And, of course, that free electrons also encounter greater resistance when moving. This is the physics of the process.

The resistivity of copper is the standard value. The values of this parameter for all metals and other substances measured at 20 ° C can easily be found in the reference table. For copper, it is 0.0175 ohm * mm2 / m. Of the metals most widely occurring in nature, this value is close in value only to aluminum. At him it is 0,0271 Ohm * mm2 / m. The specific resistance of copper in its value is second only to silver, the value of which is 0.016 ohm * mm2 / m. This causes its wide application in electrical equipment, in the manufacture of power cables, various types of conductors, for the printed installation of electronic devices. Without copper wires, it is impossible to create power transformers and motors for small household electric appliances that have the property of energy saving. In this case, the requirements to the chemical purity of the substance are substantially increased, since in the presence of even 0.02% of aluminum, the resistivity of copper is increased by 10%. Such copper, however, is considered technically clean and it is possible to make a number of certain products from it.

Without knowledge of the values of resistivity, it is not possible to calculate the overall resistance of conductors according to their size and shape when designing and designing electrical equipment. To calculate the total resistance of the conductor, we use the formula R = p * l / S, where the abbreviations denote the following:

R is the total resistance of the conductor;

P is the resistivity of the metal;

L is the length of the conductor;

S is the cross-sectional area of the conductor.

For the needs of the electrotechnical sphere, a wide production of such metals as aluminum and copper is established, the specific resistance of which is quite small. Of these metals, cables and various types of wires are manufactured, which are widely used in construction, for the manufacture of household appliances, the manufacture of tires, the winding of transformers and other electrical products.