Real World Instrumentation with Python

Electric Current

There are two fundamental phenomena involved in electricity: electric charge and electric current. Electric charge is a basic characteristic of matter and is the result of something having too many electrons (negative charge) or too few electrons (positive charge), with regard to what it would otherwise need to be electrically neutral.

A basic characteristic of electric charges is that charges of the same kind repel one another, and opposite charges attract. This is why electrons and protons are bound together in an atom, although they can’t directly combine with each other because of some other fundamental characteristics of atomic particles. The important thing to remember is that a negative charge will repel electrons, and a positive charge will attract them.

Electric charge, in and of itself, is interesting but not particularly useful from an electronics perspective. For our purposes, it’s only when charges are moving that really interesting things begin to happen. Electric current, or current flow, is the flow of electrons through a circuit of some kind. It is also what happens when the static charge you build up walking across a carpet on a cold, dry day is transferred to a doorknob: in effect, the current flows from a high potential (you) to a lower potential (the doorknob), much like water flows down a waterfall. The otherwise uninteresting static charge suddenly becomes very interesting (at least, it gets your attention).

Current flow arises when the atoms ...