electrical conductivity is called the opportunity to pass through the metal itself charged current.In turn, the resistance is called one of the characteristics of the material.The greater the electrical resistance at a given voltage, the less current.It characterizes the reaction force directed along a conductor motion of charged electrons.Since the property of conducting electricity - this is the reciprocal of resistance, expressed as the mean formulas it will be the ratio 1 / R.
Resistivity always depends on the quality of the material that is used in the manufacture of devices.It is measured, starting from the parameters of a conductor having a length of 1 meter, and the cross-sectional area of 1 square millimeter.For example, the property of the specific resistance of copper is always equal to 0.0175 ohms for aluminum - 0.029, iron - 0.135, constantan - 0.48, Nichrome - 1-1.1.Resistivity became equal to the number 2 * 10-7 Ohm • m
Countering the current is directly proportional to the length of a conductor through which it moves.The greater the length of the device, the higher the resistance.To acquire this dependence will be easier if you imagine two imaginary pair of interconnected vessels.One pair of devices connecting tube let remains thin, and the other - thicker.When filling with water both pairs move liquid in communicating vessels on the thick tube obtained much faster, because it will have less resistance to the overflow of water.For this analogy to the electric current, it is easier to pass along a thick conductor than fine.
Resistivity as SI units is measured by ohm • m.The conductivity depends on the mean free-flight of charged particles, which is characterized by the structure of the material.Metals without impurities, whose most regular crystal lattice, have the lowest values of resistance.Conversely, the impurity lattice distort than enhance its performance.The resistivity of the metal is located in a narrow range of the normal temperature from silver and 0.016 to 10 micromhos • m (alloys of iron with aluminum and chromium).
On the features of the motion of charged electrons in a conductor affected by the temperature, because when it increases the amplitude increase of wave oscillations existing ions and atoms.As a result, the electrons remains less space for the normal course in the crystal lattice.This means that the orderly movement of the obstacle increases.The specific resistance of any conductor, as usual, increases linearly with increasing temperature.For semiconductors, on the contrary, it is characterized by a decrease with increasing degrees as because of it released a lot of charges, creating an electric current directly.
cooling process some metal conductors known to bring them the desired temperature resistivity of the state and to the abrupt drops to zero.Such a phenomenon discovered in 1911 and was called superconductivity.
