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This month's installment continues a series on electrons and electricity. The material is adapted from a lesson in NCTI's Installer Technician Course. ©NCTI

For electrical activity at the subatomic level to be useful, the electrons have to flow in a reliable and predictable manner. There are two types of electron current flow. The first type is random drift and the second is directed flow.

Random drift

The movement of electrons through conductors produces free electrons. At room temperature and even very low temperatures, there is movement of atoms and agitation as they collide with one another (see Figure 1). This movement initially causes electrons to be knocked loose and then to travel randomly from one atom to another. This type of electron current flow, called random drift, is not useful. These electrons change orbits in a haphazard manner and no charge results from this random flow.

In order for electron current flow to be useful, the electrons must all move in the same direction from one atom to the next.

Directed flow

What can force electrons to all move in the same direction? Remember that two objects with opposite charges attract each other, while two charges that are alike repel each other. Therefore, electrons, all of which are negatively charged, repel each other and are attracted to a positive charge. When a negative charge is placed on one end of a wire and a positive charge is placed on the other, the electrons in the wire will travel toward the positive charge because they have been directed by the effects of the unlike charges (see Figure 2). This directed movement of electrons is called directed flow and is useful.

If a continuous positive charge is placed on one end of the wire and a continuous negative charge is placed on the other, the electrons will sustain a directed flow. For purposes of illustration only, a good way to apply a continuous charge to a conductor is with a battery (see Figure 3). Because of the chemical action of the battery, the wire receives a continuous negative charge on one end and a continuous positive charge on the other end. This forces electrons to move through the wire from the negative to the positive end until the energy in the battery is all used up and the battery "goes dead."

Note that if only a wire is connected across the terminals of a battery (as illustrated in Figure 3), no useful work is done and the battery quickly goes dead. This procedure is not recommended and is hardly ever used in actual applications.

 Back to June 2001 Issue

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