Electric Current in Metals, Liquids, Gases, Vacuum and Semiconductors
The same current, but a different traveller in every material
Big Idea: An electric current is always the ordered motion of charged particles. But which particles move depends on the material. In metals it is free electrons; in salty water it is ions; in a lamp of gas it is electrons and ions together; in a vacuum tube it is a beam of electrons flying through empty space; and in a chip of silicon it is electrons and "holes". Learn the traveller and you understand the medium.
By the end you will be able to:
- name the charge carrier in a metal, an electrolyte, a gas, a vacuum and a semiconductor;
- explain why a metal conducts better when it is cold but an electrolyte and a semiconductor conduct better when warm;
- describe gas discharge and plasma, and give examples such as lightning and neon signs;
- explain how a vacuum tube (CRT) and a semiconductor diode work in simple terms;
- use m = kIt for electrolysis and R = R0(1 + αt) for a warming wire.