Intro to ECE Design
Drs. Butera/Williams
Module:
Volts and Amps
Objectives
Upon completion of this module, you should be able to:
•
define voltage, current, and charge for DC circuits;
•
describe the roles of voltage and current in electronic circuits;
•
specify a DC power supply or battery source for a DC circuit; and
•
solve simple DC circuits with switches and resistors.
What makes it go?
Electricity “makes things happen”’ by moving
charge
down conductors. For most engineered
applications, the flow of charge is moving
electrons
down wires and connectors and through
circuit elements. Electronic circuits is the study of designing components to manipulate the
flow of charge to accomplish a task, such as lighting a light or amplifying a sound.
Electric circuits are both designed an analyzed in terms of two physical quantities that are co
dependent upon one another:
voltage
and
current
. Voltage is a measure of the potential force
available to move charge. Current is a measure of the flow of moving charges. Charges can
have both positive and negative sign. In a continuous conductive material, positive charges
flow from a higher potential to a lower potential.
While current flow is ultimately what enables circuits to perform their actions, voltage is the
quantity that is most easily controlled, measured and passed between electronic circuits.
Definitions, conventions, and units
The unit of charge is a
coulomb
(C). A single electron has a charge of 1.6
×
10

19
C. The
mathematical symbol for charge is
q
.
The unit of voltage is
volts
(V). The mathematical symbol for volts is
V
.
The unit of current is
amps
(A). The mathematical symbol for current is
I
.
Current is a
measure of the rate of flow of electrons: 1 amp = 1 coulomb/second. While the electrons
flowing in circuits have negative charge, the standard convention is to define it in terms of
the direction of flow of positive charge. In virtually all of your ECE courses, the direction
of current flow used in class and on your exams is actually the opposite direction of how the
electrons are actually moving!
While the concepts of voltage and current will be used throughout this course, we will rarely
use the term coulomb. Charge storage ability (for example, by a battery) is usually described
in terms of amphours (A
·
h). An amphour is a scaled version of coulombs (see problem
c 2010, R
OBERT
J. B
UTERA
, J
R
.
AND
D
OUG
W
ILLIAMS
P
AGE
1
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Intro to ECE Design
Drs. Butera/Williams
Module:
Volts and Amps
Prefix
Value
Name
p
10

12
pico
n
10

9
nano
μ
10

6
micro
m
10

3
milli
k
10
3
kilo
M
10
6
mega
G
10
9
giga
Table 1: SI Prefixes
sets) but is more intuitive to work with. For example, a battery that stores 3 amphours is
potentially capable of sourcing 6 amps of current for 30 minutes (or 3 amps for 1 hour, etc).
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 Fall '08
 Staff
 Alternating Current, Direct Current, Volt, Series and parallel circuits, ECE Design Drs.

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