# Specific resistance as a property of metals

Electrical conductivity refers to the ability of a metal to pass through a charged current. In turn, resistance is called one of the characteristics of the material. The greater the electrical resistance at a given voltage, the lower the amperage. It characterizes the strength of counteraction of the conductor to the motion of charged electrons along it. Since the transmission property of electricity is a value that is inverse to the resistance, it means that it will be expressed as a formula as 1 / R.

Specific resistance is always dependent on the quality of the material that is used in the manufacture of devices. It is measured by starting from the parameters of a conductor having a length of 1 meter, as well as a cross-sectional area of 1 square millimeter. For example, the property of specific resistance for copper is always 0.0175 Ohm, for aluminum - 0.029, iron - 0.135, constantan - 0.48, nichrome - 1-1.1. Specific resistance of steel is equal to the number 2 * 10-7 Ohm • m

Counteracting the current is directly proportional to the length of the conductor along which it moves. The longer the length of the device, the higher the resistance. To assimilate this dependence will be simpler if we imagine two imaginary pairs of interconnected vessels. For one pair of devices, the connecting tube remains thinner, while the other has a thicker tube. When water is filled in both pairs, the liquid transfer to the communicating vessel along the thick tube will be much faster, because it will have less resistance to the water flow. By this analogy for an electric current, it is easier for him to pass along a thick conductor than a thin one.

Specific resistance, as a unit of SI, is measured by the indicator Om • m. Conductivity depends on the average length of the free passage of charged particles, which is characterized by the structure of the material. Metals without impurities, in which the most correct crystal lattice, have the lowest values of counteraction. Conversely, impurities distort the lattice, which increases its performance. The resistivity of metals is located in a narrow range of values at normal temperature: from silver with 0.016 and up to 10 μΩ • m (alloys of iron and chromium with aluminum).

On the motion of charged particles Electrons in a conductor is influenced by temperature, because as it increases, the amplitude of wave oscillations of existing ions and atoms increases. As a result, electrons are left with less free space for a normal stroke in the crystal lattice. And this means that the obstacle to the orderly movement increases. The resistivity of any conductor, as usual, increases linearly with increasing temperature. And for semiconductors, on the contrary, the decrease with increasing degrees is characteristic, because because of this, many charges are created that create directly an electric current.

The cooling of some metal conductors, known to the right temperature, brings their specific resistance to a spasmodic state and drops to zero. This phenomenon was discovered in 1911 and was called superconductivity.