Relation between materials which allow current to easily pass through and those which require very high voltages to pass a current through them.
Different materials have different electrical conductivities.
These are based mainly on the type of material that an object is made from. For example, most metals tend to be rather good conductors of electricity, their molecular make-up is such that electrons flow from one place to another without much force. This effectively gives you a 4.5 Volt source. Now construct the simplest of series circuits using the light bulb as shown below. Note that there is a break in the circuit.