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. Although 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.
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 sets) but
is more intuitive to work with. For example, a battery that stores 3 amphours may be capable
of sourcing 6 amps of current for 30 minutes (or 3 amps for 1 hour, or 6 amps for 30 minutes,
etc).
c 2007, R
OBERT
J. B
UTERA
, J
R
.
AND
D
OUGLAS
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
Both voltage and current can be specified using standard prefixes. Commonly used prefixes are
shown in Table 1.
Practice Problems
1. A typical 1.5V AA battery has a nominal charge storage of 2600 mAh.
What is this
charge storage in terms of Coulombs?
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 Fall '08
 Staff
 Alternating Current, Direct Current, Volt, Series and parallel circuits, ECE Design Drs.

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