Resistor and Resistance

Resistor:

It is defined as an electrical element which is used to confine or limit electric current through it.

Resistance:

 The property by which a resistor opposes the flow of current is called resistance. It can also be found from ohm’s law which states that the ratio of voltage to current is called resistance.  Mathematically
                                                                   V/I = R

Unit :

The unit of resistance is ohm on the name of George Simon Ohm who gave ohm’s law and is defined as
"When one volt of potential difference causes to flow a current of one ampere through a conductor then the resistance of conductor is one ohm".
It is represented by the Greek letter omega Ω.

Explanation :

Resistance is the property of substance or material from which a conductor is made up of.  It opposes the flow of electrons i.e current. It is said to be found when moving electrons collide with each other, atoms and molecules of substance. This colliding of electrons reduces the speed of moving electrons and increases temperature as a result of release of heat due to collision. Thus we can say resistance is unfavorable property of substance that should be kept as minimum as possible in order to save heat in many cases. It decreases the efficiency of the system. However it also has some useful uses too. One of them is heater whose efficiency is 100% because here we convert all electrical energy into heat energy. One should remember that every electrical element has some resistance.

Classification of materials on the basis of resistance :

Resistance is also used to classify materials into conductors, semi-conductors and insulators.

Conductors :

The materials which offer an easy path to the flow of current are called conductors. Metals, acids and salt solutions are good conductors of electricity but silver, copper and aluminum and gold are regarded as best conductors. Copper is mostly used than silver owing to high tensile strength.

Insulators:

On the contrary, materials which do not allow flow of current through them easily but at breakdown voltages which are as high as capable to destroy materials’ configuration are called insulators. Glass, Bakelite, mica and polyvinyl-chloride (P.V.C) are best known insulators. They are used to limit current for safety reasons. 

Semi-conductors :

The materials which are to be found in between of conductors and insulators are called semi-conductors. Semi-conductors play their major role in electronics.

One should remember that every electrical element has some resistance. It means that capacitor, inductor and sources of electric current have their some internal resistance too.