One of the characteristics of any electrically conductive material - is the resistance versus temperature.If it is represented as a graph on a coordinate plane, where the horizontal axis marked intervals (t), and the vertical - the value of the ohmic resistance (R), the broken line is obtained.Resistance versus temperature schematically consists of three sections.The first corresponds to a small heat - this time the resistance changes very little.This happens to a certain point, after which the line on the graph rises sharply - a second portion.The third and last component - a straight, leaving upwards from the point at which halted the growth of R, at a relatively small angle to the horizontal axis.
physical meaning of the schedule is as follows: the temperature dependence of the resistance of the conductor is described by a simple linear equation as long as the heating value does not exceed a value that is characteristic for this particular material.Here is an abstract example: if at 10 ° C the resistance of matter is 10 ohms, and 40 ° C R value will not change, remaining within the measurement error.But even at 41 ° C there will jump to 70 ohms of resistance.If a further increase in temperature does not stop, then at each subsequent grade will fall an additional 5 ohms.
This property is widely used in various electrical devices, so regularly provide information on copper as one of the most common materials in electrical machines.So, for a copper heat conductor for each additional degree of resistance leads to increased half a percentage point from the share value (can be found in reference tables, given for 20 ° C, 1 m long section of 1 mm²).
If you have a metal conductor of the electromotive force EMF appears an electric current - the direction of movement of elementary particles with charge.Ions in the crystal lattice sites of the metal, is not able to hold long electrons in their outer orbits, so they are free to move throughout the volume of material from one node to another.This random movement due to external energy - heat.
Although the fact of moving there, it is not directed, so is not considered as current.When an electric field, the electrons are oriented in accordance with its configuration, forming a directed movement.But as the thermal influence did not disappear, then randomly moving particles collide with directional field.The dependence of the resistance of metals on temperature shows the amount of interference current flow.The higher the temperature, the higher the R conductor.
obvious conclusion: reducing the degree of heat, can be reduced and the resistance.The phenomenon of superconductivity (20 ° K) is precisely characterized by a significant reduction of thermal chaotic motion of particles in the structure of matter.
consider the properties of the conductive material is widely used in electrical engineering.For example, the dependence of the resistance of the conductor of the temperature used in the electronic sensors.Knowing its importance for any material can be manufactured thermistor, connect it to a digital or analog reader, perform the appropriate grading scale and used as alternatives to mercury thermometers.At the heart of most modern thermal sensors incorporated just such a principle, as higher reliability, and easier to design.
Furthermore, the temperature dependence of the resistance makes it possible to calculate the heating coils of electric motors.
