Resistance nature of metallic materials - Heanjia Super-metals Co., Ltd.

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Resistance nature of metallic materials

The resistance is a property of electric conductor to resist the flow of current through it. The electric resistance contributes to conceptual parallels following the concept of friction. The SI unit of resistance is ohm whereas the conductance is determined in Siemens. The nichrome resistance wire with uniform cross section offers resistance proportional to the resistivity of wire and its length and it is inversely proportion to the cross section area. Almost all substances offer certain value of resistance excluding superconductors that have zero resistance.

The resistance of object is actually the ratio of electric potential to the current flows through the resistance wire. It is also an inverse of conductance.

R = V / I or R = 1 / G.

Here R is the symbol of resistance, V is electric potential and G is conductance. For different kinds of materials and environments, the electric potential and current are directly proportion to each other whereas Resistance and conductance are always constant. However the resistance and conductance depend on different factors such as temperature and strain. This proportional rule is called ohm law and the devices that follow the ohm's law are called ohmic devices.

In certin cases of diode and battery, the electric potential and current are not directly proportional to each other so the current and potetial grah is not a straight line, so it doesn't follow the ohm's law. In such conditions the resistance and conductance are less likely refered. The ratio of potential and current is still worthy and it is called as the chordal resistance or static resistance and it refers to the inverse slop of chord drawn between orign and the curve of current and potential. In other cases the derivative of potential to curernt may not be valuable, so it is known as differential resistance.

In the hydraulic analogy evaluates current passing through circuits to the flow of water in the pipes. When the pipe is blocked up with hair, it requires high pressure to obtain the same stream of water. Giving the current through the high resistance is similar to flowing water in the blocked pipe due to hair. It also require large pressure by electromotive force to obtain the same flow of current. Following the hydraulic analogy, the current flows through the nichrome resistance wire is similar to the water passing through the pipe and the potential drop through the wire is similar to the pressure drop that drives water to the pipe. Conductance is proportional to the flow provided for the given value of pressure whereasresistance is proportional to the amount of pressure necessary to obtain the given flow. Threfore the conductance and resistance are opposite to each other.

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