11.5
Figure 1 Direct current showing the
electrons moving in one direction only.
The positive charges represent the
nuclei of the atoms and do not move.
connection to negative terminal
connection to positive terminal
e–
e–
e–
e–
e–
e–
e–
electric current
Th e movement of electrons (an electric current) is required for an electrical device
to operate. Electric current is responsible for the transfer of electrical energy along
a conducting wire. Your computer, refrigerator, stove, and battery charger simply
would not work without moving electrons in conducting wires.
direct Current
Direct current (DC) is the fl ow of electrons in only one direction through a circuit. Th e
electrons fl ow from the negative terminal of the source of electrical energy and travel
through the conducting wires toward the positive terminal.
Th e outer electrons in the atoms of a metal conductor are not tightly held to their
nuclei; rather, they move around randomly and are considered “free electrons.” When
a source of electrical energy (for example, a battery) is supplied to a circuit, free elec-
trons will move in one direction through the conductor (Figure 1). Th is movement
of the free electrons is the direct current. Th e more free electrons that are moving in
one direction, the greater is the direct current.
Th e fi rst sources of electrical energy were similar in design to batteries and all pro-
duced a direct current. In 1820, French physicist André-Marie Ampère performed
experiments on direct currents in wires. He was interested in measuring the intensity
of the current, which is why today we use the symbol I to represent electric current.
In recognition of his contributions to the understanding of electric current, the unit
of measurement for electric current is called the ampere (A). Th e equation that
describes the amount of electric current is
where I 5 current (A), Q 5 amount of charge (C), and Δt 5 time interval (s). One
coulomb of charge (or electrons) passing one point every second in a circuit is equiva-
lent to one ampere. Th erefore, 1 A 5 1 C/s. In illustrations of current, we oft en depict
only a few electrons. However, a coulomb of electrons is 6.2 × 1018 electrons. So a cur-
rent of 1 A means over 6 billion billion electrons moving past a point each second.
direct current (DC) the movement of
electrons in only one direction
I5Q
Dt
Tutorial 1 Using the Current Equation
When you are given the amount of charge and the change in time, you can use the
equation
I5Q
Dt
to fi nd the amount of current. We will apply the current equation
in the following Sample Problem.
Sample Problem 1
Calculate the amount of current through a wire that has 0.85 C of electrons passing a
point in 2.5 min.
Given: Q 5 0.85 C; Δt 5 2.5 min
Required: I
Analysis:
I5Q
Dt
Solution: Convert time to seconds to get the answer in coulombs per second,
or amperes:
Dt52.5 min 360 s
1 min
Dt5150 s
NEL
516 Chapter 11 • Electricity and Its Production
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