to be used more frequently in recent years. Technically proficient persons are
able to use either concept. Explanations involving the movement of positive
charges in one direction are no more valid than explanations involving the movement
of negative charges in the opposite direction.
b. The movement of electrons through a conductor, such as copper wire, is
an example of electron current flow (fig 1). Current flow is measured in amperes.
When 6.28 billion billion electrons pass a certain point in a conductor in 1
second, the current flow is one ampere. Electrons do not move through a conductor
of their own free will. There must be a force exerted to cause electron movement.
Figure 1.
Copper conductor.
c. The force which causes electrons to flow in a conductor is called
voltage. Voltage is the difference in electrical pressure measured between two
points in a circuit. Thus, using-a 12-volt battery as an example, the voltage
measured between the two battery posts is 12 volts. Voltage potential at a
specific point in an electrical circuit is an important concept. This simply means
the voltage or electrical pressure at a particular point with respect to another
point. If the voltage potential of one post of the 12-volt battery is zero, the
voltage potential at the other post is 12 volts with respect to the first post.
d. Polarity is another important concept. One post of a battery is said to
be positive and the other negative. By conventional theory the direction of
current flow in a circuit is from the battery or generator positive terminal,
through the external circuit, and then back to the negative terminal of the battery
or generator. This direction is opposite to the direction of electron flow.
Electron flow is generally used to explain electronic circuitry. Conventional
current flow is used to explain magnetic properties in motors and generators
(fig 2).
Figure 2.
Conventional-current flow.
OS 010, 1-P2
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