Electrical Resistance: Definition, Concept and Unit

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The electrical resistance of an item is a proportion of its restriction to the stream of electric flow. The opposite amount is electrical conductance, and is the straightforwardness with which an electric flow passes. Electrical opposition imparts some applied parallels to the thought of mechanical rubbing. The SI unit of electrical opposition is the ohm (Ω), while electrical conductance is estimated in siemens (S).

The resistance of an article depends in extensive part on the material it is made of—objects made of electrical separators like elastic will in general have high opposition and low conductivity, while objects made of electrical conduits like metals will in general have exceptionally low opposition and high conductivity. This material reliance is measured by resistivity or conductivity. In any case, resistance and conductance are broad as opposed to mass properties, implying that they additionally rely upon the size and state of an article. For instance, a wire’s opposition is higher on the off chance that it is long and slender, and lower in the event that it is short and thick. All items demonstrate some resistance, with the exception of superconductors, which have an opposition of zero.

What is Electrical Resistance? Definition, Formula and Concept

The electrical resistance is defined as the difficulty occurs in the flow of electrons. The conductor has free electrons. When the voltage or potential difference is connected over the conductor, the free electrons begin moving in the specific bearing.

During the movement, these electrons crash into the atoms and molecules of the conductor. The atoms or molecules make the obstruction in the flow of electrons. This obstruction is called resistance.

Concept of Resistance

To understand the matter let us take examples of metallic substances. There are quantities of free electrons moving arbitrarily in the gem structure of a metallic substance. At the point when a voltage is connected over the obstruction because of the electric field the free electrons float from lower potential point to higher potential point in the substance.

During drifting motion, the free electrons continually collide with atoms of the substance and this phenomenon prevents the free motion of electrons and this causes resistance.

Unit of Resistance

From the definition of resistance, it can be said that the unit of electric resistance is volt per ampere. One unit of resistance is such a resistance which makes 1 ampere current to flow through it when 1 volt potential difference is connected over the resistance. The unit of electric resistance that is volt per ampere is called ohm (Ω) after the name of great German physicist George Simon Ohm.

He is famous for his law called Ohm’s law which is applicable only on pure resistance. The unit ohm is normally used for moderate values of resistance but there may be a very large as well as a very small value of resistance used for different purposes. These values are expressed in giga-ohm, mega ohm, kilo-ohm, milli-ohm, micro-ohm even in nano-ohm range depending on the value of resistance.

Resistance of Different Materials

Depending on the resistance value substances are divided into three categories.

1. There are a few materials basically metallic substances which offer very low resistance to the current through them. These substances are referred to as conductors more unequivocally electrical conductors. Silver is an amazingly decent conductor of electricity but it is not widely used in electrical systems because of its high cost.

Aluminum is a decent conductor and it is regularly utilized conductor in light of its ease and a lot of accessibility. Copper is another great conveyor normally utilized in various electronics and electrical circuits and it is a better conductor than aluminum but at the same time, it is costlier than aluminum.

2. There is another class of materials called semiconductor. These have a moderate estimation of resistance for example not high just as not extremely low at room temperature.

There are endless uses of semiconductors for making electrons devices. Silicon, germanium are two for the most part utilized semiconductor materials. Notwithstanding these diverse mixes likewise act as semiconductors.

3. The materials offer extreme resistance to the current is known as the insulator or electrical insulation material. These materials are awful conduit of power and for the most part used to counteract spillage flow in electric frameworks. Papers, dry woods, mica, porcelain, glass epoxy polyester, mineral oil, SF6 gas, Nitrogen gas, different gases, air, and so on are genuine instances of protection materials.

Effect of Temperature on Resistance

In metallic substances with rising temperature the interatomic vibrations increment and consequently offer more protection from the development of electrons causing the current. Subsequently, with expanding temperature the opposition of metallic substances increments.

The temperature coefficient of resistance is certain for these materials. In semiconductors with expanding temperature the quantity of free electrons increments as at higher temperature progressively number of covalent bonds gets broken to contribute free electrons in the substance.

This reduces the resistance of the substance. Hence semiconductors have a negative temperature coefficient of resistance.