Conductors And Insulators

Conductors:-

Why do we always use metal wires for conduction of electricity?
Because,they are good conductors of electricity and offer less resistance to the flow of current.But how can they conduct electricity with much easy? Metals like silver and copper have excess amount of free electrons which are not held strongly with any particular atom of metals.These free electrons move randomly in all directions in the metal.When we apply an external electric field these electrons can easily move in a specific direction.This movement of free electrons in particular direction under influence of an external field cause the flow of current in metal wires.The resistance of conductor increases with increase in temperature.This is due to increase in the numbers of collisions of electrons with themselves and with the atoms of metals. 

Insulators:-

All materials contain electrons.The electrons in insulator like rubber,however,are not free to move.They are tightly bound inside atoms.Hence current cannot flow though an insulator because there are no free electrons for the flow of current.Insulators have very large value of resistance.Insulators can be easily charged by friction and induced charge remain static on their surface.Other examples of insulators are glass,wood,plastic,fur,silk etc.