Many materials have very few free electrons. A high voltage can be applied across any object, high enough to tear electrons away from atoms and enable them to carry current.
Ohm's Law states that the resistance
\[R\]
of a conductor is equal to the voltage \[V\]
divided by the current through the conductor \[I\]
and we can write \[R=\frac{V}{I}\]
. The units of resistance are Ohms (symbol \[\Omega\]
), and the ohm is defined from the equation above as the resistance of a conductor requiring a potential difference of 1 volt to produce a current of 1 Amp.More fundamental than resistance is the concept of resistivity.