r>
Below is a cache of http://www.csi.uottawa.ca/~rhabash/BIECh10.pdf. It's a snapshot of the page taken as our search engine crawled the Web.
The web site itself may have changed. You can check the current page or check for previous versions at the Internet Archive. Yahoo! is not affiliated with the authors of this page or responsible for its content.
10 1
10
Fundamentals of Electricity

OBJECTIVES

This chapter has been written to provide a better introduction to the fields of
electric circuits and electronics. We lead you through a study of the mathematics
and physics as they are jointly applied to electric circuits. After completing this
chapter you should be able to


Understand the physical meaning of variables used to describe electricity.

List the three major parts of an atom.

Define Coulombs law.

Discuss the differences between conductors, semiconductors, and
insulators.

Understand the basic quantities in electric circuits such as voltage and
current.

Understand the characteristics of resistors, inductors, and capacitors.

Define the concepts of RC and L/R time constants, which are very
important in science.

Understand the behavior of electric circuits using Ohms law.

Relate the three main parameters of an electric circuit: the voltage, the
electric current, and the electrical resistance.

Realize how the above three parameters are used to compute circuit
characteristics and conditions.

Realize how the above parameters are used to compute electrical power.

FOCUS ON MATHEMATICS

This chapter relates the application of mathematics to electrical concepts,
covering fractions; functions; vectors; derivatives and integration; exponential
equations; and graphing techniques.



2
Chapter 10
10.1 WHAT IS ELECTRICITY?

The word electricity originated about 600 B.C; it comes from elektron, which
was the ancient Greek work for amber. However, the true nature of electricity
was understood later.
What is electricity? This particular question is not easy to answer because the
word electricity has different meanings, which complement each other.
Electricity may mean electric charges, flow of electric charges, or electric energy.
If we wish to agree on a single definition of electricity, then which one should we
choose? May be we do not need to choose just one but all of the above definitions
are true.
Just as coal enabled the industrial revolution, electricity is the unseen fuel of
modern life. The dramatic increase in the use of electricity for domestic and
industrial purposes proves that electrical energy plays an important part in our
society. It is impossible to imagine what our lives would be like without access to
this source of energy. Technologies associated with electricity have made our
lives easier. Modern society is indeed unworkable without the existence of
electrical appliances. Likewise, emerging telecommunication and information
services have greatly enhanced the ability of individuals and groups to
communicate with each other and have facilitated the speed of information to
persons and machines in both urban and rural environments.
Whatever the particular field of services, possession of basic knowledge forms
the basis for the performance of many varied tasks which todays engineer is
called on by industry and employers to do-and do well.

10.2 SYSTEMS OF UNITS

In order to state the value of some measurable quantity, we must give both a
number (how much) and a unit (of what) (for example, 5 meters). Regarding
numbers, fortunately, we all use the same number system. However, this is not
true for units, and we need some efforts to familiarize ourselves with a suitable
system. This could be accomplished by following a standard unit of efficient
performance.
A measurement of any physical quantity must be expressed as a number
followed by a unit. A unit is a standard by which a dimension can be expressed
numerically. The units for the fundamental dimensions are called the fundamental
or base units. While carrying out EM calculations, there are several systems of
base units that are available. However, they may be broken into two main groups.
First, the International System of Units (SI) introduced by Griorgi in 1901,
including the meter-kilogram-second-ampere (MKSA) subsystem representing
the four fundamental dimensions length, mass, time, and electric current, Fundamentals of Electricity 3



respectively. Second is the centimeter-gram-second (CGS) system. The units for
other dimensions are called secondary, or derived units and are based on the
above fundamental units.

Table 10-1 The Seven Fundamental SI Units




Quantity Unit Abbreviation


Length meter m
Mass kilogram kg
Time second s
Electric current ampere A
Temperature Kelvin K
Luminous intensity candela cd
Matter mole mol


Currently, most the engineers use the practical MKSA system. What is known
as the Gaussian system is an unrationalized CGS system, which is mixed in the
sense that electric quantities are measured in electrostatic units, while magnetic
quantities are measured in magnetostatic units. The CGS system is used mainly in
the area of physics, where certain simplification in formulas results.
The SI is the standard system used in todays scientific literature. The SI has
seven base units, several derived units with special names, and many derived
units with compound names. A few CGS system units are also used when
appropriate. The complete SI system involves units but also other
recommendations, one of which is that multiple and submultiples of the MKSA
units be set in steps of 10
3
or 10
-3
. The fundamental SI units and abbreviations are
listed in Table 10-1. Table 10-2 lists many of the SI derived units used in electric
and electronic circuits.
The SI uses the decimal system to relate larger and smaller units to the basic
units, and employs prefixes to signify the various powers of 10. A list of prefixes
and their symbols is given in Table 10-3. These prefixes are very important in
engineering studies and are worth memorizing.
Table 10-2 SI Derived Units
Quantity Symbol Unit Unit
Symbol
Angle

Radian rad
Capacitance
C
Farad F
Conductance
G
Siemens S
Electric charge
Q
Coulomb C 4
Chapter 10
Electromotive force
E
Volt V
Energy, work
W
Joule J
Force
F
Newton N
Frequency
f
Hertz Hz
Inductance
L
Henry H
Power
P
Watt W
Resistance
R
Ohm

Pressure
p
Pascal Pa
Magnetic Flux

Weber Wb
Magnetic Induction
B
Tesla T
Light Flux
L
Lumen lm


Table 10-3 SI Prefixes
Metric Symbol
Metric Prefix
Value
Power of Ten
T One
Trillion Tera 10
12

G One
Billion Giga 10
9

M One
Million Mega 10
6

K One
Thousand Kilo
10
3

m One
Thousandth Milli
10
-3

µ
One Millionth
Micro
10
-6

n One
Billionth Nano
10
-9

p One
Trillionth Pico
10
-12



10.3 MATTER AND ELECTRICITY

To understand electricity, it is important to start with the study of atoms. The
atom is the basic building of the universe. Electricity is made up of atom matter.
Matter consists of very small particles, which together form an atom. Matter is
commonly made up of mass and weight, which occupies space. This mass can
become and take into form different states such as, solid, liquid, gas, or plasma.
The atom also has motion and two kinds of energy types: potential energy, which
is a result of its position and kinetic energy, which is the energy of motion.
An element is a substance, which cannot be reduced to a simpler substance by
chemical means. Examples of elements with which we use everyday are iron,
gold, silver, copper, and oxygen. There are now over 100 known elements. All
the different substances we know about are composed of one or more of these
elements. An atom is the smallest particle of an element that retains the
characteristics of that element. The atoms of one element, however, differ from Fundamentals of Electricity 5



the atoms of all other element