Conductor resistance

Electricity is perhaps the most energy source that has been studied by mankind and, as a consequence, has penetrated our lives so tightly that even to think that it is not there is already blasphemy. And yet, for centuries, for many centuries, people used in everyday life only an amusing toy - the attraction of a wool rubbed with small objects. This stone was the present amber, and in Greek it was called "electron". After many centuries, this name was given to the first open elementary particle - the lightest of the carrying charge. Fate proved to be supportive of the electron: it was he who became the main carrier of the energy of the electric field.

At its initial level, matter is an atomic structure of a planetary type - in the center is a nucleus of proton-neutrons and electron shells. The outer electronic shells of the atoms of the matter are exchanged by electrons, and therefore in the interatomic space of some of them, mainly those that exhibit the properties of metals, a cloud of free electrons is formed. Usually, such materials are used to produce wires for the transmission of electric current. The efficiency of current transmission is influenced by many reasons, including And the conductor resistance is an integral feature of each conductive material. If an electric voltage source is connected to the ends of the conductor , then an electric current will flow through it . The reason for its occurrence is the potential difference at the ends of the conductor. Electrons, being in an electric field, form a directed movement from a greater potential to a smaller one, along a conductor of any length, and at the same time transport the energy of the power source. Any user connected to an electrical circuit can use this energy.

The best of conductor materials are used to make wires of main lines that transmit electric current thousands of kilometers from power plants. What is the criterion for selecting the material of the conductors? This characteristic is the resistance of the conductor. How does it manifest itself in the conductor? According to the theory of electricity, free electrons move along a conductor, having a certain energy. On the way of their movement collisions with atoms of matter occur, and we have to share energy with them. We feel this "redistribution", and in fact the loss of energy, as the heating of the conductor.

Hence the eternal engineering problems, in which the main participant of the action is the resistance of the conductor. It is this parameter of the electrical circuit that determines the irrecoverable energy losses, and they grow proportionally with increasing length of the wire L. The next geometric parameter of the conductor affecting the resistance is the cross-section of the wire S. As the conductor cross-section increases, its resistance decreases proportionally. To evaluate the materials from the standpoint of their suitability for using them as a wire, one more characteristic is used, called "resistivity": this is the resistance of a conductor of 1 mm square. And a length of 1 m. Now, having previously taken from the table the value of the resistivity ƿ for the corresponding material, it is possible to calculate the resistance of the conductor. The formula gives the value R - Ohm, if ƿ - Ohm * m / mm2. , S - mm square, L - m.

R = (ƿ * L) / S.

According to the above formula, calculations can be made for any cases, if the initial data are known. And what if there is a conductor, and there are no tables and meters for the diameter and length of the wire at hand, in other words, with what device is the conductor resistance measured? In such cases, a measuring instrument is used, which is called an ohmmeter.

There are many different versions of ohmmeters that implement all possible operating principles, but most often apply current measurement schemes through the tested resistance of the conductor and a calibrated resistor or the measurement of the voltage drop across the resistor under test with a calibrated current in the measuring circuit.