Electricity is probably the most studied mankind source of energy and, as a consequence, to introduce into our lives so tightly that even think about what it is not - is sacrilege.But once, for centuries, people have used in everyday life just a fun toy - pull grated stone wool small items.This stone was present amber, and in Greek he is called "electron".Through many centuries this name has received the first open an elementary particle - the lightest of the charge carriers.Fate was kind to the electron: it became the main carrier of energy of the electric field.
at its initial level of substance is the atomic structure of planetary type - in the center of the nucleus of protons, neutrons and electrons of the shell.The outer electron shell of atoms of matter exchange electrons, so the interatomic space of some of them, especially those that exhibit the properties of metals, formed a cloud of free electrons.Typically such materials are made of wires for transmitting the electric current.The efficiency of transfer current is affected by many reasons, includingand conductor resistance - an integral feature of each conductive material.If the ends of the conductor to connect the source voltage, then it will flow electric current.The reason for its occurrence - the potential difference at the ends of the conductor.Electrons, being in the electric field, the direction of movement from the larger to the smaller capacity, along any length of the conductor, and wherein the transport energy source.Use this energy can be any user connected to the electrical circuit.
Top-conductor materials used for the manufacture of wire transmission lines that transmit electricity to thousands of kilometers from the power plant.What is the criterion for selection of the material of conductors?This characteristic is the resistance of the conductor.How it manifests itself in a conductor?According to the theory of electricity, free electrons move through a conductor, having a certain energy.On the way their movements occur collisions with atoms of matter, and we have to share with them the energy.We feel this "redistribution", but in fact the loss of energy as heat conductor.
This implies eternal engineering problems, in which the main part of the action - the resistance of the conductor.It is this parameter circuit determines the irrevocable loss of energy, and they are in proportion to the increase with wire length L. The following geometrical parameter conductor influencing resistance is the conductor cross-section S. On the increase in the cross section of the conductor, its resistance decreases proportionally.To evaluate materials in terms of their usability as a wire, applies another characteristic, which is called "resistivity": the resistance of the conductor cross section of 1 mm square.and 1 m in length. Now, after taking a table of the value of the resistivity ƿ for relevant material, we can calculate the resistance of the conductor.The formula gives a value of R - Homme if ƿ - Homme * m / sq mm., S - square mm., L - m.
R = (ƿ * L) / S.
In the above formula, the calculations can be performed for all cases, if you know the original data.And what if the conductor is, and tables and meters diameter and length of the wire is not at hand, in other words, how the instrument measures the resistance of the conductor?In such cases, the measuring instrument is used, which is called an ohmmeter.
There is also used a lot of different options ohmmeters implementing various principles of operation, but the most frequently used measurement circuit currents through the resistance of the conductor under test and a calibrated resistor or measuring the voltage drop across the resistor under test when calibrated current in the measuring circuit.
