Conductors and Insulators
"What is the use of a new-born child ?"
(when asked what was the use of a new invention)
- Moving electric charges constitute what is know as an electric
current. It is the electric currents in semi-conductor devices
which are responsible for the electronic technology in today's society.
- Conductors are materials which allow the free movement
of electric charge. Examples include,
- Some liquids
- Gas plasmas
- Insulators (or non conductors) are materials which
significant resistance to the flow of electric charge. Examples
- Non metals - plastic, wood, glass, rubber etc.
- Semi-conductors are materials whose resistance to
falls between conductors and insulators. There are very few such
materials, but their importance in electronic technology cannot be
emphasized enough. Examples,
- Mechanisms of conduction:
- Metals (solid)
- Each atom in the solid is "fixed", forming a lattice.
- Outer electrons in a metal are weakly bound to the atomic
- When an external electric field is applied these outer
through the material creating an electric current.
- Liquid conductors and gas plasmas
- Conducting liquids and gases are comprised of positive and
ions (charged particles).
- Both positive and negative ions move when an external
is applied, thus creating the current.
- A positive charge moving to the right creates the same
an equal negative charge moving to the left.
- All electrons in these materials are tightly bound to the
atomic nuclei. External electric fields are typically not large
enough to cause any flow of charge.
- These materials have a small number of weakly bound
number of which is very dependent on the temperature and
difference applied across the material.
- It is important to realise that because sustained electric
only occur when a potential difference is maintained in a closed
as many charge carriers enter as leave any part of the circuit.
other words electric current is not "used up"; it has the same value
everywhere in the circuit.
suggests to Einstein: What do you say,
professor, shouldn't we marry and have a little baby together: what a
would be - my looks and your intelligence!
afraid, dear lady, it might be the other way around...
Dr. C. L. Davis
University of Louisville