Electrons move more easily through some conductors than others when p.d is applied. The opposition of a conductor to current is called its resistance. A good conductor has a low resistance and a poor conductor has a high resistance.
The resistance of a wire of a certain material depends on its
length, cross- section and the material.
If the current through a conductor is I when the voltage across it is V, its resistance R is defined by
If V is in volts and I is in amperes, R is in Ohms.
The ohm is the resistance of a conductor in which the current is 1 ampere when voltage of 1 volt is applied across it.