Ohm’s Law is a statement of the proportionality of the current strength in the conductor to the attached voltage.
Ohm’s law is valid for metals and semiconductors at not too high applied voltage. If the Ohm’s law is valid for an element of the electrical circuit, the element can be said as having a linear current-voltage characteristic.
Ohm’s law is valid for conductors made ??of materials, which are free charge carriers: the conduction electrons, holes, or ions. If the voltage is applied to such conductors, there is an electric field in the conductors that would force carriers to move. During this movement, the charge carriers are accelerated and increase their kinetic energy. However, the increase in energy of the charge carriers is limited by collisions between themselves, and to the atoms displaced from equilibrium positions due to thermal motion of the material, to impurities. In such collisions the excess kinetic energy of the charge carriers is transformed into the heat via the vibrations of the crystal lattice.
College students writing their research paper on Ohm’s law must know that average charge carriers have a speed that is determined by the frequency of collisions. Mathematical characteristics of such collisions is time scattering and is bound with the mean free path of the charge carriers.
Calculations show that the average speed of the charge carriers is proportional to the applied electric field, and therefore voltage.
Thus, in material with free charge carriers, the current strength is proportional to the electric field voltage. The passage of current through the material is accompanied by heat release.
In strong electric fields, Ohm’s law is often not respected even for good conductors because the physical picture of the charge carriers scattering changes. Accelerated to the high speed, the charge carriers can ionize a neutral atom, giving rise to new carriers, which also in turn contribute to the electric current. Electric current increases dramatically.
In some materials at low temperatures, charge carrier scattering processes are suppressed due to the special interaction between them and the vibrations of the crystal lattice – phonons. In this case, we can observe the phenomenon of superconductivity.
In the case of AC, Ohm’s law can be extended to include consideration of elements such as an electrical circuit, characterized by the capacity and inductance. Alternating current passes through the condenser ahead for phase voltage. In AC, inductor lags the phase of the voltage. However, in both cases, the amplitude of the alternating current is proportional to the amplitude of the applied AC voltage .Mathematically it can be described by introducing complex impedance.
The verification of Ohm’s law lasted for most of the XIX century. In 1876, a special committee of the British Association held an accurate audit, imposed by Maxwell. The validity of Ohm’s law for liquid conductors were confirmed by Kohn, Fittstzherald, and Trouton.
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