b. There are two general types of electric current--direct current (DC) and
alternating current (AC).
(1) In DC, electrons flow in only one direction through a conductor. This
current may be an even or uniform flow (continuous DC) or it may move in surges
(2) In AC, electrons surge first in one direction and then in the other through
a conductor, causing a change in both amplitude (maximum level) and direction of the
SOURCES OF ELECTRIC CURRENT
Just as there must be pressure to cause a flow of water, there must be pressure
to cause the flow of electrons. If we connect a wire between a point with an excessive
number of electrons and another point with a deficiency of electrons, we will have a
potential difference resulting in a flow of electrons. The greater the difference in the
number of electrons, the greater the electrical pressure and the resulting electron flow.
Therefore, if two bodies have unequal charges, a difference of potential exists between
them. This difference of potential causes an electron current. The force needed to
move the electrons is called electromotive force (EMF) or voltage. There are two
commercially important sources of electrical pressure--chemical and mechanical.
a. Chemical. Chemical energy can be energy by a chemical reaction between
two dissimilar substances. This principle is employed in batteries.
b. Mechanical. Dynamos and generators transform mechanical energy into
in this lesson.
FUNDAMENTAL FACTORS PRESENT IN EVERY ELECTRIC CIRCUIT
In even the simplest direct current circuit, three fundamental factors are present--
a. Potential Difference. The terms potential difference, electromotive force
(EMF), potential and voltage are used synonymously.
(1) Potential difference is the difference in electrical potential existing
between two points in an electric circuit--one point has an excess of electrons (negative
charge) and the other point has a deficiency of electrons (positive charge). Attraction
between these two points supplies the force required for electrons to move between the