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Electronics Simplified
Previously published as Electronics Made Simple
Third edition
Ian Sinclair
AMSTERDAM BOSTON HEIDELBERG LONDON NEW YORK OXFORD
PARIS SAN DIEGO SAN FRANCISCO SINGAPORE SYDNEY TOKYO
Newnes is an imprint of Elsevier

Newnes is an imprint of Elsevier
The Boulevard, Langford Lane, Kidlington, Oxford, OX5 1GB, UK
30 Corporate Drive, Suite 400, Burlington, MA 01803, USA
First edition 1997
Second edition 2002
Third edition 2011
Copyright Ó 2011, 2002, 1997 Ian Sinclair. Published by Elsevier Limited. All rights reserved
No part of this publication may be reproduced or transmitted in any form or by any means, electronic or
mechanical, including photocopying, recording, or any information storage and retrieval system, without
permissioninwritingfromthepublisher.Detailsonhowtoseekpermission,furtherinformationaboutthe
Publisher’spermissionspoliciesandourarrangementwithorganizationssuchastheCopyrightClearance
Center and the Copyright Licensing Agency,can be found atour website: www.elsevier.com/permissions
This book and the individual contributions contained in it are protected under copyright by the
Publisher (other than as may be noted herein).
Notices
Knowledge and best practice in this field are constantly changing. As new research and
experience broaden our understanding, changes in research methods, professional
practices, or medical treatment may become necessary.
Practitioners and researchers must always rely on their own experience and knowledge in
evaluating and using any information, methods, compounds, or experiments described
herein. In using such information or methods they should be mindful of their own safety
and the safety of others, including parties for whom they have a professional responsibility.
To the fullest extent of the law, neither the Publisher nor the authors, contributors, or
editors, assume any liability for any injury and/or damage to persons or property as
a matter of products liability, negligence or otherwise, or from any use or operation of any
methods, products, instructions, or ideas contained in the material herein.
British Library Cataloguing in Publication Data
A catalogue record for this book is available from the British Library
Library of Congress Control Number: 2011920147
ISBN: 978-0-08-097063-9
For information on all Newnes publications
visit our website at www.elsevierdirect.com
Printed and bound in the United Kingdom
11 12 13 14 10 9 8 7 6 5 4 3 2 1

Preface
The success of the first two editions of this book has shown the continuing interest in and need
for a book that deals with the aims and methods of electronics without going into too much
detail about practical circuitry, and with the minimum of simple mathematics. This third
edition has been prepared with much more emphasis on digital electronics, now that virtually
every device available to the consumer is partly or entirely digital. The information on
microcomputers has been greatly expanded, with a separate chapter on software options.
There is an old precept that it is easier to teach digital electronics to anyone who knows about
linear electronics than the other way round. This does not apply as much as it used to, but the
analog (analogue in the UK) fundamentals are still important and they have not been dropped
in this edition. For advanced information or for details of new devices the reader is urged to
make full use of Internet search engines. For readers who are interested in electronics
construction and circuitry, please take a look at Practical Electronics Handbook, currently in
its sixth edition in the UK.
I hope that this third edition will be received as enthusiastically as were the first and second
editions, and that it is equally successful in stimulating interest in this fascinating branch of
engineering.
Ian Sinclair
xi

CHAPTER 1
Electricity, Waves, and Pulses
Fundamental Electricity
Definition
Electrical engineering is the study of generation of electrical power from other forms of power
(mainly heat, but now including mechanical systems such as wave and wind), its transmission
from one place to another, and its use, both industrial and domestic. Electronics is the branch of
electrical engineering concerned with the control of individual particles called electrons whose
movements we call electric current.
Electrical engineering is concerned with making use of electricity as a way of transmitting
and using power. There are natural sources of electrical power, such as lightning and
some living creatures, such as the electric eel, but the main concern of electrical engineering
is directed to man-made systems that generate, distribute, and use electricity. Our main
uses of electricity depend on converting electrical power to other forms, mainly into
mechanical effort, heat and light. These other forms are also our main sources of electrical
power.
The first electrical effects to be discovered were those of static electricity, observed when
amber was rubbed with silk. The ancient Greeks first discovered these effects, and because
amber is called electron in Greek, we have coined the words such as electricity and
electronics that are so familiar today. Considerably later, in the eighteenth century,
experimenters discovered other effects that also seemed to be electrical, but these were entirely
different. Typically, these effects use a chemical action to generate what we now call electric
current in a closed path that we call a circuit. As an aid to imagining what was happening,
electric current can be compared to the flow of water in pipes.
Definition
Electric current is the flow of electricity through a metal such as a cable. Electric voltage is the
electrical form of pressure that forces the current to flow.
Think for a moment about a water circuit, such as is used in central heating. The path for the
water is closed (Figure 1.1) and the water is moved by using a pump. No water is lost from the
Electronics Simplified. DOI: 10.1016/B978-0-08-097063-9.10001-9
Copyright Ó 2011 Ian Sinclair. Published by Elsevier Ltd. All rights reserved.
1

circuit and none is added. Turning off a tap at the tank (breaking the circuit) would make the
water level rise, because of the pressure of the pump, in the vertical (overflow) piece of pipe.
The pump maintains the pressure that makes the water move, and we can use this movement to
transmit power because the flowing water can turn a turbine wheel at some other part of the
circuit. Hydraulic machines depend on this idea of a liquid in a circuit, though the modern
development of hydraulics came later than our use of electricity.
It is not surprising, then, that early experimenters thought that electricity was some kind of
invisible liquid. Static electricity effects were explained as being caused by the pressure of this
liquid, and current electricity by the flow of the liquid. Electrical engineering is mainly
concerned with flow, but the later science of electronics has been based as much on static
electricity as on current flow, because we now know much more about what is flowing and why
it can flow so easily in metal wires. The fundamental quantity of electricity is electrical charge,
and that is what moves in a circuit.
Summary
Electrical effects were once thought to be caused by an invisible liquid that could flow through
metals and accumulate on non-metallic materials. Electrical engineering is concerned with the
effects of electrical flow, and most of our early applications of electricity have used the effects of
flowing electricity.
Figure 1.1:
A water circuit, which behaves in many ways like an electrical circuit
2 Chapter 1

Definition
All of the effects we call electrical are due to electric charge. Electrostatic (static electricity)
effects are caused by charge at rest, and electric current effects (including magnetism) are
caused by charge that is moving.
That definition does not tell you much unless you know something about electric charge.
No-one knows precisely what charge is (though we are slowly getting there), but we do know
a lot about what charge does, and what we know about what charge does is knowledge that has
been accumulated since the time of the ancient Greeks. We can summarize what charge does
(the properties of charge):
• When you rub two non-metallic objects together they will both usually become charged.
• These charges are of two opposite types, one called positive, the other called negative.
• Two charges of the same type (two positives or two negatives) repel each other; two
opposite charges (one positive, one negative) attract each other.
• The natural state of any substance is not to have any detectable charge, because it contains
equal quantities of positive and negative charges.
What we know about the way that charge behaves has led to finding out more about what it is,
and we know now that charge is one of the most important effects in the Universe. Like gravity,
charge is a way of distorting space, so that it appears to cause force effects at a distance from
the cause of the charge. What we call charge is the effect of splitting atoms, separating small
particles called electrons from the rest of each atom. Each electron is negatively charged, and
the amount of charge is the same for each electron. The other main part of an atom, the
nucleus, carries exactly as much positive charge as the electrons around it carry negative
charge (Figure 1.2), if we picture the atom as looking like the sun and its planets. For example,
–1
–1
–1
–1
–1
–1
+6
nucleus
Figure 1.2:
A sun-and-planet view of an atom. Though as a concept this is out of date it helps to illustrate the
idea of electrons whose total charge balances the charge of the nucleus and also the idea that the
outermost electrons can be detached
Electricity, Waves, and Pulses 3

if there are six electrons then the nucleus must carry six units of positive charge, exactly
balancing the total negative charge on the electrons.
n Note
Modern physics has long abandoned pictures of atoms as sun-and-planet systems, but
this type of picture of the unimaginable is good enough for all purposes concerned with
electrical engineering, and for most concerned with electronics.
n
When an electron has become separated from the atom that it belongs to, the attraction between
the electron and its atom is, for such tiny particles, enormous, and all the effects that we lump
together as electricity, ranging from lightning to batteries, are caused by these force effects of
charge. The forces between charges that are at rest are responsible for the effects that used to be
called static electricity (or electrostatics), and these effects are important because they are
used in several types of electronics devices.
n Note
The forces are so enormous that we can usually separate only one electron from
a nucleus, and we can separate all of the electrons only at enormous temperatures, such
as we find within the sun or in an exploding hydrogen bomb (which is what the sun
actually is).
n
Another option for an electron that has become separated from an atom is to find another atom
that has lost its electron (and is therefore positively charged). The movement of electrons from
one atom to another causes a large number of measurable effects such as electric current,
magnetism, and chemical actions like electroplating. Of these, the most important for
electronics purposes are electric current, and one of its effects, magnetism. Materials that allow
electrons to move through them are called conductors; materials that do not allow electrons to
move easily through them are called insulators.
n Note
In some types of crystals, compressing the crystal will separate charges, generating a high
voltage. These crystals are termed piezoelectric, and a typical application is as an ignition
device for a gas fire or cooker. The effect is also reversible, so that a piezoelectric crystal
can be used to convert an electrical pulse into a mechanical compression or expansion of
the crystal. This effect is used in ultrasonic cleaners.
n
The movement of electrons that we call electric current takes place in a circuit, a closed path
for electrons that has been created using conducting material. All circuits for current are closed
4 Chapter 1

circuits, meaning that electrons will move from a generator through the circuit and back to the
generator again. This is essential because unless electrons moved in a closed path like this
many atoms would be left without electrons, and that condition could not exist for long because
of the large forces that draw the electrons back to the atoms.
Definition
Electric current is the amount of charge that passes per second any point in a circuit. Electric
voltage is the amount of work that each charge can do when it moves.
These are formal definitions. We cannot easily count the number of electrons that carry charge
along a wire, and we cannot easily measure how much work is done when a charge moves. We
can, however, measure these quantities by making use of the effects that they cause. Current
along a wire, for example, will cause a force on a magnet, and we can measure that force.
The voltage caused by some separated charges can be measured by the amount of current that
will flow when the charges are allowed to move. The unit of current is called an ampere or
amp, and the unit of voltage is a volt. These terms come from the names of the pioneers
Ampere and Volta, and the abbreviations are A and V, respectively.
n Note
We can create less formal definitions for ourselves. Voltage is like a propelling force
for current, and current itself can be thought of as like the current of a river. If we
continue with this idea, voltage corresponds to the height of the spring where the river
starts.
n
All substances contain electrons, which we can think of as being the outer layer of each
atom. Some materials are made out of atoms that hold their electrons tightly, and when
electrons are moved out of place it is not easy for them to return to their positions. In
addition, other electrons cannot move from their own atoms to take up empty places
on other atoms. We call these materials insulators, and they are used to prevent electric
current from flowing. In addition, insulators can be charged and will remain charged for
some time.
A good example is the party balloon which is charged by rubbing it against a woolen sweater
and which will cling to the wall or the ceiling until its charge is neutralized. Surprisingly high
voltages can be generated in this way on insulators, typically several kilovolts (kV), where
kilo means one-thousand. For example, 5 kV means five-thousand volts. A very small current
can discharge such materials, and we use the units microamp (mA), meaning a millionth of an
amp, nanoamp (nA), meaning a thousandth of a millionth of an amp, and picoamp (pA),
meaning a millionth of a millionth of an amp. There is an even smaller unit, the femtoamp (fA),
one-thousandth of a picoamp.

n Note
As a comparison, the electrical supply to a house in the UK is at 240 V 10%, 50 Hz and
currents of 1 A to 13 A are used in domestic equipment (though electric cookers can use
up to 30 A). In the USA, the minimum supply voltage is 110V to 115V, and the maximum
is 120V to 125V, at 60 Hz, with higher currents (requiring thicker wiring).
n
Now let’s look at electricity with lower voltages and higher currents. This is the form of
electricity that we are most familiar with and which we use daily.
Steady Voltage
There are several ways of generating a steady voltage, but only two are important for everyday
purposes. Batteries are the most familiar method, and the invention of the first battery by
Alessandro Volta in 1799 made it possible for the first time to study comparatively large
electric currents at voltage levels from 3 V to several hundred volts. A battery is, strictly
speaking, a stack of cells, with each cell (Figure 1.3) converting chemical action into electrical
voltage. In the course of this, a metal is dissolved into a metal-salt, releasing energy in the form
of electrical voltage that can make current flow.
n Note
If the released energy were not converted into electrical form it would be converted to
heat, which is what most chemical changes provide. As it is, if you take a large current
from a battery you will find that it gets hot.
n
Figure 1.3:
A typical cell, the familiar zincecarbon type. The voltage output is 1.5 V for a fresh cell, and the
current that can be drawn depends on the size of the cell, up to a few amperes. The electrical energy
is obtained at the expense of chemical energy. The acid dissolves the zinc case, releasing electrons so
that the case is negative. The charge accumulates on the carbon rod. The depolarizer removes
hydrogen gas which otherwise acts as an insulator
6 Chapter 1

For centuries the zincecarbon type of cell, and a few others, were the only types known, but in
the later twentieth century several other types were discovered. One of these, the lithium-ion
(often abbreviated to L-ion), is totally different in construction and delivers more than 3 V,
unlike other types that provide a maximum of 1.5 V. Just to confuse matters, there is also
a lithium cell (not lithium-ion) that provides just 1.5 V but has a much longer useful life than
the older types.
Some types of cell, such as Li-ion and nickelemetal hydride (NiMH), are rechargeable, so that
you can connect them to a (higher) voltage and convert the metal-salt back to the metal e but
you need to use more energy than you got out of the cell. As always, no energy is ever created.
If anyone ever tries to sell you a motor that runs on air, magnetism, or moonbeams, always
ask where the energy comes from (usually it is from the people who have been cheated along
the way). You can always detect a charlatan by the way that he or she uses spoof-science
phrases like tapping into our natural energy field (and they usually bring crystals into their
vaporings as well).
Another way of generating a steady voltage was discovered by Michael Faraday in 1817. He
demonstrated the first dynamo, which worked by rotating a metal disk between the poles of a
magnet, using the energy of whatever was turning the disk (Faraday’s hand first of all, and later
a steam engine) converted into electrical voltage that could provide current (Figure 1.4).
Strictly speaking, a voltage that is the result of a generator or a battery should be called an
electromotive force (EMF), but this name is slightly old-fashioned nowadays.
Figure 1.4:
Faraday’s first electrical generator. When the disk is spun, a voltage (EMF) appears between the
contact points or brushes. The voltage is very small, but the principle can be applied to make
a dynamo

n Note
Later, Faraday found that higher voltages could be generated by substituting a coil of
wire for a metal disk, and this is the basis for modern generators, though the original
Faraday principle (the homopolar dynamo) is still in use for specialized applications.
n
In these pioneering days, steady (or direct) voltage was the only type that was thought to be
useful. A steady voltage will cause a steady current to flow when there is a path of conducting
material, a circuit, between the points where the voltage (the EMF) exists. We call these points
terminals. A cell or a simple dynamo will have two terminals, one that we call positive and
the other negative. When a wire, or any other conductor, is used to connect the terminals,
a current will flow, and if the voltage is steady, then the current also will be steady. That does
not mean that it will be steady for ever. A cell will be exhausted when its metal is all dissolved,
and the voltage will fall to zero. A dynamo will generate a voltage only for as long as the shaft
is turned. By convention, we say that the current flows from the positive terminal to the
negative terminal (even though we know now that the electrons move in the opposite
direction).
A steady voltage will cause a steady current, called direct current (DC), to flow, and in 1826
Georg Simeon Ohm found what determined how much current would flow. He called this
quantity resistance. The three quantities, voltage, current, and resistance, are therefore related,
and the unit of resistance is called the ohm in his honor. For any part of a circuit, we can
measure the voltage across the circuit (between one end and the other) and the current through
the circuit and so find the resistance.
Definition
When a current of I amps flows, using a voltage of V tubevolts, then the resistance R ohms is
equal to voltage divided by current. In symbols, this is R ¼ V/I, and we can write this also as
V ¼ RI or I ¼ V/R.
n Note
This relationship is often, wrongly, called Ohm’s law. The correct definition of Ohm’s
law states that this quantity called resistance is constant for a metal that is used to
conduct current at a steady temperature. What this boils down to is that we can use the
relationship in any of its three forms with R constant if the resistance R is of a metal at
constant temperature. In other words, if 6 V causes 2 A to flow through a resistance,
then 12 V will cause 4 A to flow through the same piece of metal (whose resistance is
3 ohms, written as 3 U. This is not true when some non-metal materials are used, or if
a metal is allowed to get hot. For example, the current through a semiconductor obeys
8 Chapter 1

I ¼ V/R, but the value of R is not constant, it changes for each value of current. Similarly,
a torch bulb has a much higher resistance when it is hot than it has when it is cold.
We cannot use Ohm’s law assuming a constant value of resistance for these examples.
n
We can determine whether or not a conducting material obeys Ohm’s law by plotting a graph of
current against voltage, using a circuit as in Figure 1.5(a). If this results in a graph that is
a straight line (Figure 1.5b), then the material obeys Ohm’s law; it is ohmic. Most metals
behave like this if their temperature is kept constant. If the graph is curved (Figure 1.5c) the
material is not ohmic, and this type of behavior is found when metals change temperature
considerably or when we use semiconducting materials in the circuit.
Power
Power is the rate of doing work, meaning the amount of work done per second. When we
use electricity, perhaps for heating, lighting, running a motor, or plating gold on to a base
metal, we are making use of power, converting it from the electrical form to other forms. The
Figure 1.5:
Voltage, current and resistance. (a) The voltage (EMF) of a cell is used to pass current through
a sample of conducting material: the ratio of voltage across the sample to current through the
sample defines the resistance; (b) ohmic graph; (c) one form of non-ohmic graph

amount of power that is dissipated or converted can be calculated easily for anything that uses
steady voltage and current; it is equal to the figure of volts multiplied by the figure of current.
When this power is converted into heat we often call it dissipation because we cannot contain
it; it leaks away. The calculation of power, in symbols, is:
Power ¼ V I
where V is in volts and I is in amps. The unit of power is the watt, abbreviation W. As an
example, if the torch bulb is rated at 3 V 0.5 A then its power is 1.5 W.
Things are not so simple when we are working with quantities that are not steady, but we can
always find the amount of power by making measurements of volts and amps and carrying
out a multiplication. The difference is that for changing voltages and currents we need to
multiply by another factor as well; we will look at that later when we deal with RMS quantities
and phase angles.
Alternating Voltage
The voltage (EMF) that is generated by a cell or battery is truly steady, but the voltage from
a rotating generator is not. When one side of the revolving coil of wire is approaching a pole of
the magnet, the changing voltage is in one direction, but as the wire moves away from the
magnetic pole, the changing voltage is in the other direction. Because there are two poles to
a magnet, the voltage from a rotating coil rises and falls twice in a revolution, positive for half
the time and negative for the other half. This is an alternating voltage, alternately in one
direction and then the other direction. The graph looks like that of Figure 1.6, and the time it
takes to go through one complete cycle of the waveshape is the time that it takes to turn the coil
through a complete revolution. The snake shape of the graph gives rise to the name sinewave,
from the Latin word for ‘snake’.
Figure 1.6:
A sinewave that can be produced by rotating a coil between the poles of a magnet. This is the form
of AC wave used for electrical supplies and also for radio carrier waves (see later). Radio carrier
waves are generated by circuits called oscillators rather than by rotating machines
10 Chapter 1

Faraday’s later type of dynamo got around this reversal of current by using a mechanical switch
called a commutator, which reversed the connections to the coil twice on each revolution, just
as the voltage passed through zero (Figure 1.7). This generated an EMF which, though not
exactly steady, was at least always in the same direction, so that it was possible to label one
terminal as plus and the other as minus. If the shaft of the dynamo is spun quickly enough, there
is in practice very little difference between the voltage from the dynamo and the same amount
of voltage from a battery. For tasks like heating, lighting, electroplating, battery charging, and
so on, the supplies are equivalent.
There are other ways of generating electricity from heat and from light, but they suffer the
problems of inefficient conversion (not much electrical energy out for a lot of heat energy in) or
low density of energy (for example, you have to cover a lot of ground with light cells to
generate electricity for a house). A few small generators use nuclear power directly, by
collecting the electrons that radioactive materials give out, but large-scale nuclear reactors use
the heat of the reaction to generate steam and supply it to turbines. These are therefore steam-
powered generators, and the only difference is in how the steam is obtained (and the hysteria
that is generated).
The same is true of the places on Earth where steam can be obtained from holes in the ground,
providing geothermal power, but this steam-power is less controllable and certainly not
available everywhere. Higher efficiency figures can be obtained where heat is not involved,
such as in hydroelectric generators. Wind turbines, in contrast, require the variable voltage that
they generate to be turned into a constant voltage and frequency (see later) and these
conversions reduce the already low efficiency. If we were really serious about spending money
Figure 1.7:
Principle of the dynamo. The coil generates a voltage that is alternating, but by reversing the
connections on each half turn, the output voltage is in one direction (a unidirectional voltage).
Modern dynamos use slip-rings and semiconductor circuits (see Figure 2.18) rather
than the old-fashioned commutator (which wears out because of sparking and
mechanical rubbing)

wisely we would try to develop tidal or wave generators that would serve the additional
function of protecting our coasts from erosion.
n Note
Incidentally, we could count electricity generated by solar heating as nuclear, because the
Sun, like other stars, is a gigantic nuclear furnace. The difference is that you do not (yet)
get demonstrators demanding that the Sun should be shut down or moved. Unlike
chemical energy, electricity cannot be stored in any useful quantity so we have to
generate as much as we use.
n
Summary
Voltage (EMF) can be generated by converting energy (mechanical, chemical, or heat energy)
into electrical form. A cell converts chemical energy into a steady voltage, but only for as long as
there is metal to supply the energy. A dynamo uses mechanical energy and will generate a voltage
for as long as the shaft can be turned by a steam engine, wind-power, a waterwheel, or whatever
source of energy is at hand. The output of a dynamo is not steady, but is in one direction and can
be used for the same purposes as truly steady voltage.
Alternating Current and Waves
If we omit the commutator of a dynamo and connect to the ends of the coil rotating at a steady
number of revolutions per second, the graph of the voltage, plotted against time, shows a shape
that is a sinewave, as was illustrated in Figure 1.6. The connection to the coil can be made using
slip-rings (Figure 1.8), so as to avoid twisting the connecting wires. This voltage is an
N S
out out
coil
magnet
slip-rings
Figure 1.8:
Slip-rings provide a way of connecting wires to each end of a rotating coil
12 Chapter 1

alternating voltage and when we use an alternating voltage in a circuit, the current that flows
is alternating current (AC). A graph of current plotted against time is of the same shape as the
graph of voltage, and the peak of current is at exactly the same time as the peak of voltage in
each direction if the circuit contains only resistances.
n Note
In practice, the rotating portion is usually a magnet that uses current in a coil (an
electromagnet), and the slip-rings carry the steady current that magnetizes this rotor.
The output is taken from a coil wound on the non-rotating portion (stator), so that the
much larger output current does not have to be passed through a brush and slip-rings.
This device is called an alternator, and its most familiar form is the generator in your car.
The AC output from the alternator is converted into DC to charge the battery.
n
We can use AC for electrical heating, for electric light, for motors, and in fact for most
domestic uses of electricity. It cannot be used for electroplating or battery charging, however,
and it cannot be used for most types of electronic equipment. In the nineteenth century,
when electronics was in its infancy, the advantages of AC greatly outweighed any minor
disadvantages, particularly since AC could be converted to DC if DC were essential. What
are the advantages of using AC?
• AC is the natural output from a rotating generator, requiring no commutators or other
reversing devices.
• Alternating voltage can be converted up or down (using a transformer; see later) without
using any mechanical actions. For example, if you generate at 5 kV you can convert this
up to 100 kV or down to 240 V with negligible losses. The higher the voltage you
convert to, the longer the distance you can connect by a cable of reasonable size. This
makes the National Grid possible, so that generating stations need not be close to
users of electricity.
• Very simple motors can be made that use AC and which will run at a constant speed (used
for clocks, gramophone motors, and tape-recorder motors).
• AC can be used to power vibrating motors, such as used for electric shavers.
• AC can be converted to DC for electronic equipment, and can be used to provide several
different steady voltage levels from one AC supply.
Virtually every country in the world therefore generates and distributes electricity as AC,
and the convention is to use a rate of 50 cycles per second (50 hertz or Hz) in Europe
or 60 cycles per second (60 Hz) in the USA. In terms of a simple generator, this corresponds to
spinning the shaft of the generator at 3000 revolutions per minute (r.p.m.) for 50 Hz, or 3600
r.p.m. for 60 Hz. The abbreviation Hz is for hertz, the unit of one cycle of alternation per
second. This was named after Heinrich Hertz, who discovered radio waves in 1884.

n Note
Most of Europe uses AC at 240 V, 50 Hz, but US domestic appliances need thicker cables
than their European counterparts (for the same amount of power) because a higher
current is needed to provide the same power at the lower voltage.
n
Summary
DC is the natural output of a battery, but AC is the natural output of a rotating generator. AC
is used worldwide for generating and distributing electricity, mainly because it makes it possible
to have a large distance between the generator and the user. Since AC can be converted to DC
much more easily than converting DC to AC, there are no problems in using an AC supply for
electronics circuits that require a steady voltage supply.
Electronics
Definition
Electronics is a branch of electrical engineering that is concerned with controlling charged
particles such as electrons and holes. We will introduce the idea of holes now.
Atoms such as those of metals can be so tightly packed together that they can share electrons,
and the loss of an electron from a set of these packed atoms does not cause such a large upset in
any one atom. In these materials, electric current can flow by shifting electrons from one set of
atoms to the next. We call these materials conductors. All metals contain closely packed
atoms, and so all metals are conductors, some much better than others. A small voltage,
perhaps 1.5 V, 6 V, 12 Vor so, can push electrons through a piece of metal, and large currents
can flow. These currents might be of several amps, or for very low voltages perhaps smaller
amounts (see earlier) measured in milliamps (mA), microamps (mA), picoamps (pA), or even
femtoamps.
n Note
Pure liquids, other than liquid metals such as mercury or gallium, are not good
conductors, but liquids with dissolved salts will conduct because when a salt dissolves in
water (for example), the solid salt is split into charged particles called ions. These ions
can move, so that the solution will conduct electricity. Note that the word ‘salt’ means
any compound made by combining a metal and a non-metal, of which common salt
(sodium chloride) is the most familiar example.
n
14 Chapter 1

As well as being closely packed, the atoms of a metal are usually arranged in a pattern,
a crystal. These patterns often contain gaps in the electron arrangement, called holes, and these
holes can also move from one part of the crystal to another (though they cannot exist beyond
the crystal). Because a hole in a crystal behaves like a positive charge, movement of holes
also amounts to electric current, and in most metals when electric current flows, part of the
current is due to hole movement and the rest to electron movement.
There are some materials for which the relative amount of electrons and holes can be adjusted.
The materials we call semiconductors (typically silicon) can have tiny amounts of other
materials added to the pure metal crystals during the refining process; this action is called
doping. The result is that we can create a material that conducts mainly by hole movement
(a P-type semiconductor) or one that conducts mainly by electron movement (an N-type
semiconductor). In addition, the number of particles that are free to move (free particles) is less
than in a metal, so that the movement of the particles is faster (for the same amount of current)
than it is in metals, and the movement can be affected by the presence of charges (which attract
or repel the electrons or holes and so interfere with movement). The movement can also be
affected by magnets. Semiconductors are important because they allow us to control the
movement of electrons and holes in crystals.
Summary
• All materials can be charged, for example by dislodging electrons. For every positively charged
material there is a negatively charged material, because charging is caused by separating
electrons from atoms, and the electrons will eventually return.
• The movement of electrons is what we detect as electric current, and the ‘pushing force’ for
the current, caused by the attraction between positive and negative, is called voltage.
• Voltage is the cause of current.
• Materials can be roughly classed as conductors or insulators. Conductors have closely packed
atoms which can share electrons, so that electron movement is easy, and electric current can
flow even with only a small voltage. Insulators have more separation between atoms,
electrons are not shared, and even a very high voltage will not cause any detectable current to
flow. When we work with conductors we use low voltage levels and comparatively high
currents. When we work with insulators we can use high voltage levels and very low currents.
• The third class of material is the semiconductor. Semiconductors can be natural, but better
results are obtained by refining materials and deliberately adding impurities that will alter
the number of free electrons or holes. The importance of semiconductors is that they make it
possible to control the flow of charged particles, and this is the whole basis of modern
electronics.
n Note
Before semiconductors were discovered, electronic vacuum tubes (called valves in the
UK) were used to control electron (not hole) flow. The principle, dating from about
1904, is that when electrons move in a vacuum, their movement through a wire gauze

(or grid) can be controlled by altering the voltage on the grid. Vacuum tubes are still used
where large voltages and currents have to be controlled, such as for high-power radio
transmitters, and also for cathode ray tubes (for older television receivers and for the
measuring instruments called oscilloscopes), but their use for other purposes has died
out. Even the oscilloscope requirement is now being replaced.
n
Electromagnetic Waves
AC would be important enough even if it only provided a way to generate and distribute
electrical power, but it has even greater importance. A hint of this came in 1873 when James
Clerk Maxwell published a book containing equations that showed that an alternating voltage
could generate waves of voltage and magnetism in space, and that these waves would travel at
the same speed as light. He called these waves electromagnetic waves, and from there it was
a short step to show that light was just one of these waves.
Why just one? These waves differ from each other in two ways. One is the number of waves
that pass a fixed point per second, called the frequency of the waves. The other is the
amplitude (the amount of rise and fall in each wave) (Figure 1.9). Amplitude determines the
energy of the wave, so that a large amplitude of a light wave means a bright light. Frequency
affects how easily a wave is launched into space and how we detect it.
Definition
Low-frequency electromagnetic waves are called radio waves, and we generate them and detect
them nowadays using electronic methods. To put figures to these quantities, waves with
frequencies below 100 kHz (one-hundred-thousand complete cycles per second) are classed as
very low frequency (VLF) and are used mainly for time signals and for some long-distance
communications. Waves of around 1 MHz (one-million hertz) frequency are called medium-
wave, and a large number of entertainment radio transmitters use this range. Waves in the range
10 MHz to around 50 MHz are classed as short waves, used for communications, and the very
high-frequency (VHF) range 50 MHz to 200 MHz is also used for similar purposes. As the
frequency is increased, the range of useful communications along the Earth’s surface decreases,
but the range in space (as from a satellite to Earth) is much greater.
n Note
The amplitude that is quoted for a wave is usually the peak amplitude. The figure of
peak-to-peak amplitude is used when the wave is not symmetrical.
n
The range from 300 MHz to 1000 MHz is ultra-high frequency (UHF), used for television
transmissions, and once we get to using the unit of GHz (1 gigahertz is equal to 1000 MHz)
16 Chapter 1

then the signals are in the microwave ranges, used for mobile phones, satellite
communications, and radar. These names are only rough indications of a range, and because
we have found it necessary to use higher and higher frequencies over the years we have had
to invent names for new ranges of frequencies that we once thought were unusable.
n Note
Of all the possible microwave frequencies, only one (2.45 GHz) has a strong heating
effect on anything that contains water. Other frequencies, such as are used for mobile
phones and other communications (including satellite broadcasting), cause only
negligible heating effects on materials unless very high powers are used.
n
One lower frequency range is particularly significant to us, and is called the audio range. This
is the range of frequencies between about 30 Hz and 20 kHz, and its significance is that this is
the range of frequencies of sound waves that we can hear (bats might have a different
definition). A microphone, for example, used in a concert hall would provide an electrical
output that would consist of waves in this range. For speech, we make use of a much smaller
range, about 100e400 Hz.
n Note
A microphone is an example of an important device called a transducer. A transducer
converts one form of energy to another, and for electronics purposes, the important
transducers are those that have an input or an output which is electrical, particularly if
that input or output is in the form of a wave. For audio waves, the output transducer
(converting electrical waves into sound waves) is a loudspeaker.
n
Figure 1.9:
Amplitude. The peak amplitude figure is used for symmetrical waves, like sinewaves. Peak-to-peak
readings are used for waves whose shape is not symmetrical

All the electronic methods that we know for generating waves are subject to some limitation at
the highest frequencies, and methods other than electronic methods of generating and detecting
waves have to be used. At around 1000 GHz, the waves are called infrared, and their effect
on us (and any other objects) is a heating effect on all materials that absorb the waves, so
that we can detect these waves coming from any warm object. We can also use electronic
transducers to convert infrared signals into electrical signals. Higher frequencies, to about
100,000 GHz, correspond to the infrared radiation from red-hot objects, and one small range
of frequencies between 100,000 and 1,000,000 GHz is what we call light. Higher still we have
X-rays, gamma rays and others which we find very difficult to detect and cannot generate for
ourselves.
As far as electronics is concerned, we make most use of the waves in the range from a few hertz
to several tens of gigahertz, and radio technology is concerned with how these waves are
generated, used to carry information, launched, and detected. Radio, in this respect, includes
television and cellular telephones, because the use of the waves is the same; only the
information is different.
Waveforms
The waveform of a wave is its shape, and because an electromagnetic wave is invisible the
shape we refer to is the shape of the graph of (usually) voltage plotted against time. The
instrument called the oscilloscope (see Chapter 17) will display waveforms; we do not need to
draw graphs from voltage and time readings. We are seldom particularly interested in the shape
of the waves that are transmitted through space, and waveforms are of interest mainly for
waves that are transmitted along wires and other conductors in electronic circuits.
The simplest type of waveform is the shape of the wave that is generated by the magnet and coil
arrangement that Faraday used (which was illustrated in Figure 1.6). The shape that this
generates is called a sinewave (or sine wave) and it is the same shape as a graph of the sine of
an angle plotted against the angle. What makes the sinewave particularly important is that any
other shape of wave can be created by mixing sinewaves of different frequencies, and any
shape of wave can be analyzed in terms of a mixture of sinewaves.
Though a pure sinewave is the simplest wave, its uses are confined to AC power generation and
to radio transmitters. Most of the waves that we use in electronics are a long way from
a sinewave shape, and one special type, the pulse, has become particularly important from the
second half of the twentieth century onwards.
Take a look at the two shapes in Figure 1.10. Wave (a) is called a square wave, for obvious
reasons, and it is used particularly when a wave is used for precise timing. Because the
edges of the wave are sharp, each can be used for starting or stopping an action. If you used
a sinewave there would be some uncertainty about where to start or stop, but the steep edge of
18 Chapter 1

the square wave makes the timing action much more certain. For example, the time needed
to change the voltage level of such a wave might be only 50 nanoseconds or less (1 nanosecond
is a thousandth of a millionth of a second).
The square wave is nothing like a sinewave, and it can be generated naturally by switching
a steady voltage on and off rather than by any type of rotating generator. Very precise square
waves are generated by electronic circuits that use a vibrating quartz crystal to control the
frequency, and these circuits are used in clocks and watches. Even greater precision is obtained
from the atomic clock that uses the natural vibration of atoms as a fixed frequency.
The other wave, in Figure 1.10(b), is called a sweep in the USA or a sawtooth in the UK. It
features a long, even, rise (or fall) followed by a fast return to the starting voltage. Before 1936,
a wave of this shape would have been an academic curiosity, but this is the shape of wave that is
needed for a cathode ray tube, for television, or for radar, and we will look at it again in
Chapters 8 and 17. The sawtooth is also an important waveform that is used in electronic
measuring instruments.
What marks these waves out as totally different from the sinewave is that they show very
sharp changes of voltage. A sinewave never changes abruptly; its rate of change is fixed by
its frequency and amplitude. These square and sawtooth waves can change in a time that
bears no relation to the frequency or the amplitude. A square wave might have a frequency of
only 1 Hz, but change voltage in less than one-millionth of a second (a microsecond, written
as 1 ms).
Summary
The waveform is the shape of an electrical wave, and the most fundamental waveform is the
sinewave that is generated by a coil rotating between the poles of a magnet. The important
features of a waveform are its frequency, the number of times a wave repeats per second, and its
amplitude, the height of the wave. Sinewaves are used mainly in radio applications, but other
waveshapes such as square and sawtooth waves are used, particularly where timing is important.
Figure 1.10:
Other waveforms: (a) square waves; (b) sawtooth or sweep waveform

Pulses
The pulse is a waveform, but one that you might not recognize as a wave because the time of
the pulse is very short compared to the time between pulses. Figure 1.11 illustrates three
different pulse shapes, all of which share a very sharply rising portion, the leading edge. For
a negative pulse, this leading edge would be a sharp fall in voltage.
Definition
A pulse is a rapid change in voltage which is of very short duration compared with the time
between pulses.
For example, a pulse might repeat at a rate of 1 kHz, 1000 pulses per second. The actual pulse
might have a duration, a pulse time, of only 10 ms, so that the change in voltage lasts only for
10 ms in the 1 ms (millisecond) between pulses. That makes the time of the pulse (its duty
cycle) 1/100 of the time between pulses, and these are fairly typical figures. Pulses are used for
timing, and they have the advantage that they use very little energy because the change in
voltage is so short. A pulse can be used to start an action, to stop an action, or to maintain an
action (such as keeping a wave in step, synchronized, with the pulses).
Modern digital electronics systems, particularly computers, rely heavily on the use of pulses,
and when we work on these systems we are not greatly concerned about waveshapes, only
about pulse timing. There are many things that can change a waveshape, making it very
difficult to preserve the shape of a wave. By contrast, it is more difficult to upset pulse timing
by any natural means, so that circuits which depend on pulse timing are more reliable in this
respect than circuits that depend on waveshapes.
Figure 1.11:
Examples of pulse waveforms. The common factor is a sharp leading edge
20 Chapter 1

The classic example is sound recording. Hi-fi systems in the past tried to work with a waveform
that had a very small amplitude (the output from a gramophone pickup) and keep the shape of
the waveform in the form of a copy that had a much larger amplitude. This large-scale copy
was used to operate loudspeakers, and we called the whole exercise amplification.
The problem with this system is that a copy of the waveform is never perfect, something that is
even more obvious when you make a copy of a copy. Any blemish on the surface of the record,
any false movement of the stylus, any interfering signals in the circuits all will make the copied
waveform inaccurate, a process we call distortion.
Nowadays the sound is recorded digitally as a set of pulses, using the pulses to represent
numbers, and each point in a waveform is represented by a number. Using pulses for counting,
we can ensure that the numbers are not changed, so that when the stream of numbers is
converted back to a wave, the shape of the wave is exactly the same as was recorded. This is the
basis of compact discs, the most familiar of the digital systems that have over the last few years
replaced so many of the electronics methods that we grew up with. There will be more of all
that in Chapters 11 and 12.
Actions on Pulses
There are two actions that can be carried out on pulses and on square-shaped waves that are
important for many purposes. One of these is differentiation, and this can be achieved by
passing a pulse or square wave into a circuit that selectively passes only the fast-changing
part of the input. Figure 1.12 shows the result of differentiating, which converts the pulse or
square wave into a pair of sharp spike shapes. These spikes are very short pulses, and we can
use them for timing. We can select either a positive or a negative spike by using other
circuits.
The other action is called integration, and it is a form of averaging or smoothing. A typical
action is illustrated in Figure 1.13, showing a set of pulses as the input to an integrating
circuit (an integrator). The output is a steady rise in voltage, and eventually this will become
Figure 1.12:
Differentiating action, illustrated on two waveforms. The action emphasizes the sharply changing
portions of the waves

steady at a value which is the peak voltage value of the pulses. This is the opposite action to
differentiation, removing rapid changes from a waveform.
There is another waveform that is very important in almost all branches of electronics, the
sawtooth or sweep wave. This is obtained by integrating part of a square wave, and was
illustrated earlier in Figure 1.10(b). The steady rise (or fall) of voltage is called the sweep
portion, and the rapid return (the portion that is not integrated) is called the flyback. We shall
meet this type of wave again in connection with television, oscilloscopes, and digital
voltmeters.
Summary
Pulse and square waveforms have sharp changes of voltage and can be used for timing.
These waveforms can be differentiated or integrated by using suitable circuits. The action of
differentiation emphasizes sharp changes in a wave; the opposite action of integration smooths
out sharp changes.
Definition
Electronic circuits can be divided into analog and digital types. Analog circuits are used to
operate on waves, preserving the shape of the wave. Digital circuits work with pulses and the
shape is not important, only the timing.
Early applications for electronics required actions such as amplification, the creation of a copy
of a wave with larger amplitude. The type of circuits used for these actions are classed as
analog circuits. As the twentieth century progressed, circuits that counted using pulses became
more important and such circuits are digital circuits. At present, digital circuit methods are
steadily replacing the older analog methods, and this progress is reflected in this book.
Figure 1.13:
Integrating action. The action smooths out sharp changes, altering a steep rise into a sloping rise,
for example
22 Chapter 1

CHAPTER 2
Passive Components
Electronic components are the building blocks of an electronic circuit, and all electronic
circuits are created by joining components together. At one time this was done by soldering
wires between the terminals of components, but nowadays the connections are more likely
to be made using metal tracks on an insulating board (a printed circuit board or PCB).
On a PCB holes are drilled into the metal tracks, so that components located on the
insulated side can be attached and connected by pushing their connecting wires through the
holes so that the wires can be soldered to the metal track. We will come back to that in
Chapter 5. Often now both the connections and the components are all contained in a single
piece of silicon, the integrated circuit (IC), which we shall look at in Chapter 3. In such
a circuit, both steady and alternating voltages will exist together, and several types of
components do not behave in the same way to alternating voltages as they do to steady
voltages.
In addition, components can be active or passive. Active components are used to copy
(amplify) waveforms and to switch voltages and currents on and off under electrical control.
Such active components need an input signal (a waveform) to control an output signal, and
they also need some source of power, which is usually a steady voltage supply. A circuit that
contains active components can produce an output waveform which provides more power
(voltage multiplied by current) than its input waveform. In other words, active components can
provide amplification of power.
n Note
There are passive components, such as transformers, that can provide amplification of
voltage (but at reduced current) or amplification of current (at reduced voltage), but not
amplification of power.
n
Passive components always reduce the power of an input waveform, so that an output wave
from a circuit that contains only passive components is always at a lower power than (or the
same power as) the input. Passive components do not need any additional steady voltage supply
to enable them to deal with waveforms. A complete electronic circuit will normally consist of
both active and passive components, arranged so that the passive components control the action
of the active components and act as a path for signal waveforms. Take a look now at the most
common passive components, resistors, capacitors, and inductors.
Electronics Simplified. DOI: 10.1016/B978-0-08-097063-9.10002-0
Copyright Ó 2011 Ian Sinclair. Published by Elsevier Ltd. All rights reserved.
23

Resistors
Resistors are the most common of passive components. We saw in Chapter 1 that the quantity
called resistance connects current and voltage, so that in any circuit or part of a circuit, the ratio
voltage/current(V/I)istheresistance.Ifwemeasurethevoltageacrossaresistorinvolts(V)andthe
currentthrough theresistor in amps (A),then the resistanceisin units ofohms(U).UsingtheGreek
letter omega for ohms avoids the confusion that would be inevitable if we used a capital letter O.
Definition
A resistor is used to control current or to convert a wave of current into a wave of voltage, using
the I ¼ V/R or V ¼ RI relationship.
Everypart ofa circuit has someresistance tothe flow ofcurrent,and when wespecify aresistor as
a circuit component we mean a component that is manufactured to some precise (or reasonably
precise) value of resistance and used to control the amount of current flowing in some part of
a circuit. Though it is possible to manufacture resistors with low values of a fraction of an ohm,
most of the resistors that we use in electronics circuits have higher values of resistance, and to
avoid having to write values like 15,000 U or 2,200,000 U we use the letter k to mean ‘thousand’
and M to mean ‘million’ and we omit the omega sign. In addition, the letter R is often used to
mean ohms, because typewriters (which, unlike word-processors, do not have the omega
symbol) are still being used. Another way of making values clearer is to use the letters R, k or M
in place of a decimal point, because decimal points often disappear when a page is photocopied.
For example, using these conventions, you would write 15,000 U as 15k and 2,200,000 U as
2M2. A resistance of 1.5 U would be written as 1R5, and a resistance of 0.47 U would be written
as 0R47. The small letter m can be used to mean milli, so that 4.7 mU means 0.0047 ohms.
Resistors can be manufactured to practically any value that you want, but in practice there is no
point in having a vast range. A standard set of preferred values is used, and this also fits in
with the manufacturing tolerances for resistors and other components. For example, the
standard values of 1.0 and 1.5 allow manufacturing with 20% tolerance with no rejected
resistors. This is because if you take any pair of values on the scale, then a value which is 20%
high for one value will overlap the amount which is 20% low for the next value. For example,
20% up on 1.0 is 1.0 þ 0.20 ¼ 1.20 and 20 down on 1.5 is 1.5 0.3 ¼ 1.2, so that these values
can overlap: a resistor of value 1R2 could be a 1R0 which was on the high side or a 1R5 which
was on the low side. We can pick numbers from the standard set (for 5% tolerance) to suit 10%
or 20% tolerances, as Table 2.1 shows. Resistors with 20% tolerance are hardly ever used
nowadays because modern electronics demands more precise values.
The preferred value numbers need only be in the range shown here, because we can
multiply or divide by 10 to obtain other ranges. For example, the number 4.7 can be used
24 Chapter 2

in the form 4R7 for 4.7 U, or as 0R47 (0.47 U), 47R, 470R, 4k7, 47k, 470k, 4M7, 47M,
and so on.
n Note
Resistor values are indicated on the body of resistors using a color code, though on
sub-miniature components the value is often printed in alphanumeric characters (and
may need a magnifying glass to read). See Appendix B for details of the color code, and
websites that show the shape of typical components.
n
Summary
Resistors are manufactured using a range of preferred values that ensures there will be no rejects.
Tolerances of 1% and 5% are commonly used, and closer tolerances can be obtained. Values are
often written using the letter R in place of the ohm sign or the decimal point, and using k (kilo) to
mean thousand and M (mega) to mean million. This allows a value to be specified without the
need to write a large number of zeros.
Table 2.1: Preferred values for
5%, 10%, and 20% tolerance.
5% 10% 20%
1.0 1 1
1.1
1.2 1.2
1.3
1.5 1.5 1.5
1.6
1.8 1.8
2
2.2 2.2 2.2
2.4
2.7 2.7
3
3.3 3.3 3.3
3.6
3.9 3.9
4.3
4.7 4.7 4.7
5.1
5.6 5.6
6.2
6.8 6.8 6.8
7.5
8.2 8.2
9.1
Passive Components 25

A resistor behaves in the same way to all voltages and currents, whether these are steady
voltages (or currents) or waveform voltages (or currents). In other words, the relationship
V ¼ RI is always true for a resistor that is kept at a constant temperature (Ohm’s law). When
a current passes through a resistor there will be a voltage across the resistor, and power is
converted into heat (Figure 2.1). Just as the V ¼ RI relation can be written in three ways, the
power equations also exist in three forms.
Wherever there is resistance in a circuit, electric power is converted into heat, and this
represents dissipation, waste, loss of energy. In addition, the conversion of electrical
energy into heat means that the temperature of a resistor will rise when it is passing
current. Unless the resistor can pass on this heat to the air it will overheat and be damaged.
Figure 2.1 shows the relationship between voltage, current, resistance, and lost power, and
also shows the symbols that are used to represent a resistor on a circuit diagram. Both the
block and the zigzag symbols are in use, but in Europe the block is the preferred symbol
nowadays.
This power loss (dissipation) is always associated with resistance (whether of resistors or in
other components). If the dissipation is large some method has to be used to keep the
components from overheating, and this usually takes the form of cooling fins so that the
heat can be more efficiently transferred to the air. There are some components (such as
capacitors, see later) that do not dissipate any measurable amount of heat, but any circuit
will inevitably contain some resistors whose heat will spread to other components. Heat
dissipation is particularly important in a circuit that contains active components, as we shall
see in Chapter 3.
When a resistor carries a steady current, there will be a steady voltage across the resistor
(V ¼ RI); and when there is a steady voltage placed across a resistor, there will be a steady
Figure 2.1:
Power dissipated by a resistor. There are three versions of the formula, so that you can use whichever
is most suitable. For example, if you know values of R and I, use the RI2
formula
26 Chapter 2

current (I ¼ V/R) through the resistor. The relationship applies also to waves, so that if
a waveform of current passes through a resistor there will be a voltage waveform across the
resistor whose value can be found from V ¼ RI. When a resistor is used like this to obtain
a voltage wave from a current wave, we call it a load resistor. Load resistors are used along
with active components.
n Note
When we use these V ¼ RI relationships with alternating currents and voltages, we
normally use peak values for both voltage and current. Another option is to use root
mean square (RMS) values (see Chapter 4) for both quantities. Whatever type of
measurement you use must be used consistently: you cannot multiply a peak value of
voltage by an RMS value of current and get anything useful.
n
Resistors can be used to reduce the amount (amplitude) of a signal. Suppose, for example, that
we connect two resistors in series (one connected to the end of another) as shown in Figure 2.2.
If a signal voltage is connected across both resistors, as illustrated, then the output across just
one single resistor is a smaller signal voltage, and the size of this signal can be calculated from
the sizes of the resistors. As a formula, this is:
Vout ¼ Vin
Ry
ðRy þ RxÞ
and it allows us to adjust signals to whatever amplitude we want to use. Suppose, for example,
that Ry in Figure 2.2 is 10k and Rx is 15k, and we have a 20 V signal at the input. Since the total
resistance is 25k, the output is 20 10/25, which is 8 V.
Figure 2.2:
The potentiometer or voltage divider circuit. The output voltage is a fraction of the input which can
be calculated if the resistor values are known

n Note
The dot that is placed where lines join in this circuit diagram is a way of emphasizing that
these lines are electrically connected. When you see lines crossing, with no dot, on a modern
circuit diagram this means that there is no connection between the lines. Older diagrams
usedahumptoindicatealinecrossing.Wewilllookinmoredetailatcircuitdiagramslater.
n
The combination of two resistors (Figure 2.2) is called a potentiometer or an attenuator, and
we can manufacture a component, an adjustable (variable) potentiometer which allows us to
vary the values of both resistors together, keeping the total resistance constant. The symbol is
shown in Figure 2.3, and you can think of it as a resistor with an extra contact that can be
moved in either direction. This allows the output voltage to be adjusted (by altering the position
of the contact) from the maximum (which is the same as the input) to zero. The potentiometer
can be used, for example, as a volume control in a radio.
n Note
The resistors in Figure 2.2 are connected in series, meaning that the current must pass
through both resistors equally, one after the other, making the voltages across each
resistor different unless the resistance values are the same. The alternative is parallel
connection, in which the current splits between the resistors. When components are
connected in parallel, the voltage across each of them is the same but the currents
through each will be different unless the resistance values are the same. You will see
several examples of series and of parallel connections in the course of this book.
n
Summary
The main use of resistors is to control current or as load resistors to convert current waves into
voltage waves. The relationships V ¼ RI, I ¼ V/R and R ¼ V/I hold for either steady or alternating
voltages and currents provided the same types of units are used. Two resistors in series can be
used to reduce (attenuate) a signal voltage, and a variable version of this arrangement is
a potentiometer, used to adjust signal levels.
Figure 2.3:
The variable potentiometer symbol. This component is used to provide an adjustable voltage
division and a typical use is as a volume control
28 Chapter 2

Capacitors
A capacitor is a gap in a circuit, a sandwich of insulating material between two conductors
which has capacitance (see later). As far as DC is concerned the capacitor is a break in the
circuit, but a capacitor will allow AC to pass, so that it allows us to separate AC from DC. The
symbol for a capacitor (Figure 2.4) shows it as two conducting plates with a gap between them,
and this can be used as a way of manufacturing capacitors, though we more usually find a solid
insulator between the plates.
Two exceptions are variable capacitors and electrolytic capacitors. Variable capacitors use two
sets of plates that mesh with each other (not touching), and because one set of plates is carried
on a spindle, turning the spindle will alter how much the plates mesh, and so alter the (small)
capacitance between them. This has been used widely in the past for tuning radios. The
electrolytic capacitor, by contrast, uses an acid jelly held between metal plates, and the
insulator is hydrogen gas that is generated by chemical action. This type of capacitor is used
when a very large value of capacitance is needed in a small volume.
As far as steady voltages or currents are concerned, the capacitor is just a gap, a break in a circuit
so that no steady current can flow. When you place a steady voltage across a capacitor there is no
steady current (but there can be a momentary current, as we shall see later). It is a different
matter when an alternating voltage is used. When you move electrons on to one plate of
a capacitor, the same number of electrons will leave the other plate, because of the electrostatic
effect of like charges repelling each other. When you move electrons alternately to and from one
plate, the same waveform will occur on the other plate, just as if it had been connected through
a circuit. You can measure the alternating voltage across the capacitor and the alternating current
through it and find the size of quantity which is given by V/I. This quantity is called capacitive
reactance, and given the symbol XC. This has units of ohms (because it is a ratio of voltage to
current), but it is not the same as resistance. We will come back to that point later.
Unlike a resistor, a capacitor does not have a fixed value of this reactance quantity, because if
you change the frequency of the supply wave, the reactance of a capacitor will change. When
frequency increases, reactance decreases, and when frequency is decreased, reactance
increases. There is, however, a quantity called capacitance which depends on the physical
Figure 2.4:
The capacitor symbol. The basic symbol is this parallel-plate type (a) that indicates the nature of
a capacitor as a pair of conductors separated by an insulator. (b) The symbol for an electrolytic
capacitor, used for large capacitance values

measurements of the capacitor and the type of insulating material between the plates, not on the
frequency of the voltage waveform. The value of capacitive reactance can then be calculated if
you know values for capacitance and for the frequency of the alternating voltage.
Definition
When a charge, amount Q, is placed on the plates of a capacitor, there will be a voltage V
between the plates. The capacitance C is defined as C ¼ Q/V, with charge measured in coulombs
(Q) and V in volts, while the unit of capacitance is farads. This, however, is not a practical way of
measuring capacitance because it is difficult to measure charge precisely.
The natural unit for capacitance is the coulomb per volt, called the farad (named after Michael
Faraday), but this unit is too large for most of the sizes of capacitors that we use for electronics
circuits. We therefore use the smaller units of microfarad (mF), nanofarad (nF), and picofarad
(pF). A microfarad is one-millionth of a farad, the nanofarad is one-thousandth of microfarad,
and the picofarad is one-millionth of a microfarad. For example, a variable capacitor might
have a maximum value of 300 pF; an electrolytic capacitor might have a value of 5000 mF.
Capacitors of 1 F or more can be manufactured for use as backup supplies in low-consumption
electronics circuits.
Summary
A capacitor consists of an insulator between conducting plates, and does not pass steady
current. Alternating voltages will cause an alternating current to pass through a capacitor, and
the ratio of V/I is constant if the frequency is not changed. This ratio is called capacitive
reactance, measured in ohms. A more fundamental quantity, called capacitance, can be
calculated, in units of farads, from the dimensions of a capacitor and the type of insulator, and
this quantity is a constant for a capacitor. The reactance at any frequency can be calculated from
the capacitance value.
When an alternating voltage is applied to a capacitor and alternating current flows, the voltage
wave is not in step with the current wave, but occurs one-quarter of a wave later (Figure 2.5).
Contrast this with the behavior of a resistor, which is also illustrated in this diagram. Because
the maximum current through a capacitor happens at the time of zero voltage, and the
maximum voltage happens at the time of zero current, there is no power dissipation from
a perfect capacitor (one which has no resistance). Nothing is perfect, but capacitors get pretty
close in this respect and their dissipation is usually almost immeasurably small.
The amount by which voltage and current are out of step is expressed as a phase angle. If you
think of a cycle of a wave as being caused by a coil rotating between the poles of a magnet, one
complete wave corresponds to one complete turn of the coil, turning through 360. On this
basis, half a wave corresponds to 180 and quarter of a wave to 90. We say, then, that the
capacitor causes a 90 phase shift between voltage and current for an alternating supply, with
30 Chapter 2

the current wave ahead of the voltage wave. We say that in the capacitor, current leads voltage
or, looking at it the other way round, that voltage lags current.
n Note
This idea of phase is very important in all branches of electronics, and you will need to
recall it when we look at stereo radio broadcasting and color television principles. Phase
is a quantity that we can alter for a wave just as we can alter frequency or amplitude, and
when we use the idea of phase we are always comparing one wave with another. So far,
we have been comparing a current wave with a voltage wave at the same point in
a circuit, but you could equally compare the phase of one voltage wave with another, or
compare the phase of a wave at one point in time with the phase it had earlier.
n
When a circuit contains a capacitor the wave of voltage in that complete circuit will not be in
step with the wave of current. Suppose, for example, that a circuit contains both a capacitor and
a resistor. The wave of voltage across the resistor will be in step with the current wave, but the
wave of voltage across the capacitor will not be in step with the current wave through the
capacitor. The result is that the total voltage across the circuit cannot be calculated simply.
For example, in the circuit of Figure 2.6, the total voltage VT is not equal to VC þ VR. There are
ways of calculating this, but they are a long way from simple addition, and this book is not
concerned with mathematics. Another consequence of this is that the power dissipated in the
resistor is no longer found by multiplying voltage and current, because the peak voltage does
Figure 2.5:
Phase angle. The phase of voltage across the capacitor is a quarter of a wave time (90) later than
the phase of current (which is also the phase of the voltage across the resistor)

not occur at the same time as the peak current (because of the phase shift). To be mathematical
for a moment, the power has to be found from the equation:
P ¼ V I cos F
where F is the phase angle between voltage and current. If F is 90 then cos F ¼ 0, and the
power dissipated is also zero.
n Note
The cosine (or cos) of an angle is a quantity that varies between 0 and 1, depending on
the size of the angle. A graph of cosine of angle plotted against angle from 0 to 360 is
a waveform shape of graph (a sinewave shifted by 90).
n
Summary
Alternating current through a capacitor is one-quarter of a wave, 90, ahead of the wave of
voltage. This has two effects. One is that there is no dissipation in a capacitor except from the
resistance of its conductors. The other is that the presence of a capacitor in a circuit causes the
waves of voltage and of current in the whole circuit to be out of step.
Charge and Discharge
Capacitors act as insulators for steady voltages, and as reactances for waves, but their behavior
both with steady voltages and with changing voltages such as pulses is also important. The
capacitor can accumulate a tiny amount of electrical charge when it is connected to a steady
voltage, but if the connection is made (as it almost always is) through a resistor, then this
Figure 2.6:
One effect of phase shift is that the total voltage across a series R and C circuit is not equal to the
sum of the separate voltages across the components
32 Chapter 2

charging action takes time, even if this time is measured in microseconds, and the time is not
a simple measurable quantity.
Look, for example, at what happens in the circuit shown in Figure 2.7(a). This shows a voltage
supply with a switch, a resistor, and a capacitor. Starting with the switch open, so that the circuit
is disconnected, there will be no voltage across the capacitor. When the switch is closed, current
flows momentarily and it will charge the capacitor, but as the voltage across the capacitor
increases the amount of current is reduced (if you think in terms of water pouring through a pipe
into a jug it has a shorter distance to fall), so that the rate of charging slows down.
The result is that a graph of voltage across the capacitor plotted against time takes the form
shown in Figure 2.7(b). This is the type of graph shape that is called an exponential rise, and
what makes it interesting is that it is, in theory, never totally complete. If we have a charged
capacitor and we connect a resistor across its terminals, the voltage plotted against time will
give the graph shape called an exponential decrease. Mathematically, the graph is described
using a universal constant called ‘e’, the exponential constant which also appears in
calculations of things you might think were not related, such as compound interest, population
growth, or the decay of radioactivity. A convenient rule of thumb for capacitor and resistor
combinations makes use of what is called a time constant.
Definition
The time constant of a combination of a capacitor and a resistor is the value of capacitance
multiplied by the value of resistance. If the capacitance value is in units of farads and the
resistance is in units of ohms, the time constant R C is in units of seconds. More practical units
are kU for the resistor and nF for the capacitor, giving time in ms. For example, using a capacitor
of 20 nF and a resistor of 100k gives a time constant of 2000 ms, which is 2 ms (milliseconds).
The importance of the time constant is that we can take it that charging or discharging is over
for all practical purposes (meaning about 95%) after a time of three time constants. For more
Figure 2.7:
Charging a capacitor through a resistor. In this circuit (a), the voltage across the capacitor rises with
a rate that is not constant, giving a curved graph (b). This is an exponential increase

precision, a value of four time constants can be used, but we will stay with the value of three
times in this book. This makes it easy to work out the times for the waveform that is produced
when a resistor and capacitor are used in a charging or a discharging circuit. Suppose that
a resistor is connected across a charged capacitor, as in Figure 2.8. The shape of the voltage/
time graph is then as shown in the drawing, once again taking the process as being complete
after three (or four) time constants.
For example, if the input to the circuit of Figure 2.9 is a square wave whose flat portion
takes more than three time constants, we can draw the output waveform fairly easily. The
first part is a charging curve taking three time constants, and the last part is a discharging
portion that also takes three time constants. If the top of the square wave had a duration of more
than six time constants, the remainder is unaffected. The effect is one that we noted in
Chapter 1, of integration of the square wave.
Figure 2.10 shows a slightly altered circuit in which the components are rearranged and the
output voltage is across the resistor. Now when there is a sudden rise of voltage at the input, the
capacitor has no time to charge, and the voltage across it is zero, which means that all of
the input voltage appears across the resistor. Then as the capacitor charges, the voltage across
the resistor drops to zero in the time of three time constants. If the input is then suddenly taken
back to zero the process repeats, with the voltage across the resistor dropping (so that the
capacitor maintains its change), and then reducing to zero in three time constants. This is the
action of a differentiating circuit.
Figure 2.8:
Discharging a capacitor through a resistor. The graph shows an exponential decrease, and we can
take it as being complete in three time constants
Figure 2.9:
The effect of this type of circuit on a square wave, showing the time in terms of time constant t. This
is an integrating circuit
34 Chapter 2

Inductors
An inductor is a coil of wire (or any other shape of conductor wound in a circle). Since this
wire has resistance, an inductor will pass steady current when there is a steady voltage across it,
but the fact that the wire is wound into a coil makes it behave as more than just a resistance for
alternating current. If the resistance is low, we find that the alternating current through the coil
lags almost 90 behind the alternating voltage across the coil, as illustrated in Figure 2.11,
which also shows the symbol for an inductor.
For any inductor, the value of reactance can be measured, an inductive reactance, equal to
alternating voltage divided by alternating current, using the units of ohms for reactance. This
quantity is constant only for a fixed frequency. If you increase the frequency of the alternating
voltage, the reactance of the inductor also rises.
Figure 2.10:
The differentiating form of the circuit. Remember that the voltage across the capacitor cannot
change instantly, so that when the voltage changes suddenly on one plate it must make the same
change on the other plate, after which charging or discharging will alter the voltage
Figure 2.11:
Phase angles in a circuit containing an inductor and a resistor. The phase of voltage across the
inductor (assuming it has no resistance) is 90 ahead of the phase of current (which is also the phase
of the voltage across the resistor)

Once again, there is a quantity, called inductance, that can be calculated from the dimensions
of the coil and knowledge about its magnetic core (if any core is used). This quantity of
inductance is constant for a coil. The more turns there are on the coil, the greater the
inductance, and the inductance is also (greatly) increased when the coil is wound on a magnetic
material (a core). Inductance is measured in units called henry (H), named after the American
pioneer Joseph Henry. We often use the small units of millihenries (mH) and microhenries
(mH), and the abbreviation letter for an inductor is L.
Inductors are far from perfect: they have resistance because they are made from wire, so that
there is always some dissipation from a coil, and the phase shift is never exactly 90. Most of
the coils that we use, however, have much larger values of reactance than of resistance, and
the imperfections are not too important. Modern electronic circuits avoid the use of
inductors as far as possible, but when they are used their symbol reminds you that an
inductor is a coil.
n Note
Some applications call for very small inductance values. One example is a resonant circuit
(see later) for a television ultra-high-frequency tuner or for a satellite receiver. To make
the very small values of inductance the wire does not even need to be coiled, and it is
more usual to see a flat strip of metal used in place of a coil.
n
Summary
A coil of wire is simply a resistor as far as steady voltage is concerned, but for alternating voltages
it behaves as an inductor. An inductor has inductive reactance, and causes a phase angle of
almost 90 between current and voltage, with the voltage wave leading the current wave. The
resistance of the wire means that an inductor is never perfect, but at the higher frequency ranges,
the reactance can be very much greater than the resistance. The inductance of a coil can be
calculated from its dimensions, and used to find reactance at any frequency. Reactance increases
as frequency is increased. The dissipation in an inductor is only the amount you would expect
from the resistance of its conductors.
n Note
Why does a coil behave so differently to AC? The reason is that the AC generates
changing magnetism around the coil, and the changing magnetism generates an
alternating voltage that is out of phase, opposing the voltage that drives the alternating
current through the coil. The net effect is to oppose current just as a resistor opposes
current (though for a different reason).
n
36 Chapter 2

n Note
The combination of a resistor and an inductor also forms a time constant, but in practice
this combination is seldom used in the way that we use resistorecapacitor time
constants.
n
Transformers
The simplest transformer consists of two coils of insulated wire wound over the same core of
magnetic material, one coil for input, the other for output. This has no effect as far as steady
voltages are concerned, but for an alternating voltage the effect is very useful. When an
alternating voltage is applied to one of the two coils, called the primary, this will generate an
alternating voltage at the same frequency across the other coil, the secondary.
The ratio of these voltages is, ideally, the same as the ratio of the number of turns in the coils.
For example, if the secondary coil has half the number of turns that the primary coil has, then
the AC voltage across it will be half of the AC voltage across the primary. This arrangement is
a step-down transformer, and you can just as easily make a step-up transformer, for which
the voltage across the secondary coil is greater than the voltage across the primary.
Figure 2.12 shows the circuit symbol and an elementary form of construction for a small
transformer.
n Note
What is happening depends on two effects. One is that the alternating current flowing
through the primary winding creates alternating magnetism of the core, just as a steady
current would create a steady magnetism. The other effect is that the alternating
magnetism will generate an alternating voltage in the secondary coil, but a steady
magnetism would not generate any voltage. The core acts as a magnetic link between the
windings.
n
There is no gain of power in a transformer; it is a passive component and there will always be
a loss of power. If you have 100 Vacross the primary coil and 1 A flowing, and a secondary that
gives 200 V, then the secondary current cannot exceed 0.5 A. That is assuming no resistance
and therefore no losses. We can come reasonably close to this perfection in very large
transformers, such as are used on the National Grid, but not on small transformers unless they
are being used at frequencies much higher than the normal 50 Hz or 60 Hz (USA) of the power
mains. You can always expect loss of power in any small transformer, and this is indicated by
a rise in temperature.

The transformer was invented by Michael Faraday, and it is the main reason for our use of AC
for electricity distribution. Transformers allow us to convert one alternating voltage into
another with only very small losses (caused by the resistance of the wire in the coils). We can
generate electricity at a voltage which is convenient, such as 25 kV (25,000 V), and convert
this to 250 kVor more for transmission, because for the same power level, the current flowing
in the cables will be one-tenth of the current from the generator. The less the current, the lower
the power that is dissipated.
This is why we use pylons for electricity transmission, because we need to keep a large distance
between cables at 250 kV (or more) and the earth. This is also why burying cables is ruinously
expensive, because even if you can insulate the cables adequately, the cable will act as one
plate of a capacitor (the earth being the other) and the alternating current will flow between the
cable and earth. Since this is not exactly a perfect capacitor (the earth is moist) there will be
heavy losses. If it is essential to bury cables, we need to use DC in the cables, adding more
complication. It also adds another set of losses of valuable energy. Some of the proposals we
see for dealing with our electricity generation would end up with us living in dark (but very
green) caves.
The main use of transformers in electronics is in converting the 240 VAC mains supply to the
low DC voltage that is needed for electronics in the power supply unit (PSU). The transformer
converts the 240 V AC of the mains into a suitable lower voltage, and other components then
convert this low-voltage AC into low-voltage DC.
Summary
When two coils are wound on the same magnetic core the result is a transformer. A transformer
can change voltage and current levels with almost no loss of power. The ratio of (AC) voltages for
a transformer is, ideally, the same as the ratio of the number of turns in the windings.
Figure 2.12:
The transformer: (a) simplest practical arrangement; (b) symbol
38 Chapter 2

Resonance
We have seen that both capacitors and inductors affect the phase angle between current and
voltage for AC. The effect, however, is in opposite directions, and a useful way to remember
this is the word C-I-V-I-L. Say this as ‘C e I before V; V before I for L’ to remind you that for
a capacitor (C) the current (I) wave comes before the voltage (V) wave, but the voltage wave
comes before the current wave in an inductor (L). The US version of this is E-L-I-I-C-E, using
E for voltage.
Suppose a series circuit contains both capacitance and inductance along with the inevitable
resistance such as in Figure 2.13. How does such a circuit respond to alternating voltages? We
can, of course, rule out any possibility of steady current, because the capacitor will act like
a break in the circuit as far as DC is concerned. The interesting thing is that if we pass an
alternating current, the voltage across the capacitor will be in opposite phase, 180, to the
voltage across the inductor (because, compared to the current, the voltage across the inductor is
90 leading and the voltage across the capacitor is 90 lagging) (Figure 2.14). The total voltage
across the reactive components is the difference between the voltage across the inductor and the
voltage across the capacitor.
This becomes particularly interesting when the reactance of the inductor is exactly the same
size as the reactance of the capacitor. When this is true, as it must be at some frequency, then
the sum of the reactances, in opposite directions, will be zero, and all that is left is the
resistance due to the resistor, which can be quite small. This condition is called resonance, and
in this series resonant circuit the current is maximum (equal to V/R, where R is the circuit
resistance) at resonance. A graph of current plotted against frequency, near the frequency of
resonance, looks as in Figure 2.15.
Vc
VL
VR
AC
Figure 2.13:
A circuit containing capacitance, inductance, and resistance in series.
This is a series resonant circuit

Definition
A resonant circuit is one in which the effects of capacitance and inductance cancel each other
out for one particular frequency.
There is another way of connecting a capacitor and an inductor (with the inevitable resistance)
(Figure 2.16). This is a parallel connection, and in this circuit, DC can pass because the coil is
a wire connection. If we apply only an alternating current supply, however, we find that this
time the alternating voltage (rather than the current) becomes a maximum (not a minimum) at
the frequency of resonance when the reactances are equal in size.
Figure 2.14:
How the voltages across the capacitor and across the inductor oppose each other. These voltages,
for a perfect inductor, cancel each other out exactly at the frequency of resonance
Figure 2.15:
How the current varies with the frequency for a series resonant circuit. This allows a particular
frequency to be selected, but the series circuit is less common for practical uses than its counterpart,
the parallel resonant circuit
40 Chapter 2

A resonant circuit can act like a selective transformer, delivering an output which is at a much
larger voltage or current than the input, for one particular frequency (in practice, a small range
or band of frequencies centered around one frequency). This is the effect that allows a radio or
television to be tuned to one of a set of transmitting stations, using the selective transformer
effect of the resonant circuit.
Resonant circuits are also important for timing and for transmitting signals. A piece of quartz,
made in the form of a capacitor that uses the quartz as an insulator, will behave like a resonant
circuit, with a step-up ratio at resonance that is much higher than can be achieved by any
combination of inductor and capacitor, so that these quartz crystals are used to control the
frequency of transmitters and also in clocks and watches.
Summary
When an inductor and a capacitor are used in the same circuit, their phase shifts are in opposite
directions. When the sizes of the reactances are equal, the effects cancel so that for alternating
signals, the only effect is of resistance. For a series circuit, this causes the current to be
a maximum at the resonant frequency and for a parallel circuit the voltage is a maximum at
resonance. The resonance effect is used for selecting a frequency or a small range (a narrow
band) of frequencies for purposes such as radio tuning. A quartz crystal can be made to resonate,
and is more efficient than any inductor/capacitor combination, so that quartz crystals are widely
used for timing and frequency setting.
Figure 2.16:
The parallel resonant circuit. The voltage V across this circuit is a maximum at the
resonant frequency

Diodes
A diode is a passive component, but its construction follows the methods that are used for
semiconductors (which are active components). A diode can be used with either steady or
alternating supplies, but all resemblance to a resistor ends there, because a diode is not ohmic
(see Chapter 1). A diode passes current in one direction only, and this is indicated by an
arrowhead on the symbol that is used (Figure 2.17). The diode terminals are named anode and
cathode, and in normal use current passes only when the anode is at a higher positive voltage
than the cathode.
This illustration also shows a typical graph of current plotted against voltage. Unlike the
corresponding graph for a resistor, this graph shows both positive and negative scales for current
and voltage, because this allows us to show that the diode conducts in one direction only, and that
it is not ohmic. The graph line is not straight even when the diode is conducting, so that there is
no single figure of resistance that can be used; you cannot specify a 3k3 diode, for example. The
resistance is very high when the current is low, and becomes lower as current is increased. Even
when the voltage across a diode is in the forward (conducting) direction, the current is almost
undetectable until the voltage has reached a threshold level of around 0.56 V for a silicon diode.
n Note
A diode will break down, making it useless, if a large enough reverse voltage is applied,
allowing excessive current to flow in the reverse direction. Diodes can be manufactured
whose reverse breakdown voltage is precise and stable, and these Zener diodes (see later
in this chapter) are used for providing a stable voltage level.
n
Figure 2.17:
The diode and its graph of current plotted against voltage. Even in the forward conduction
direction, there is no current flowing when the voltage is small (typically 0.4 V for diodes
constructed from silicon). There is no current in the reverse direction unless a very large reverse
voltage is applied, which will cause the diode to break down (becoming open circuit)
42 Chapter 2

The effect of a diode on an alternating voltage supply is illustrated in Figure 2.18. The effect is
like that of a commutator, allowing only half of the waveform to appear at the output. This
effect is used in converting AC into DC, and also for a task called demodulation of radio
waves (see Chapter 6). The circuit illustrates the simplest conversion circuit, half-wave
rectification, and the much more common full-wave bridge circuit. A diode is a passive
component, though the methods that are used to manufacture diodes are also used to
manufacture active components.
Figure 2.19 shows a typical simple PSU which uses a diode rectifier bridge circuit along with
electrolytic capacitors and a voltage stabilizer IC. The transformer supplies AC at a suitable
(low) voltage and the output of the transformer is connected to the input of the diode bridge
circuit. The input to the stabilizer is a voltage that is higher than we need at the output, typically
þ18 V for a 12 Voutput. The stabilizer contains a voltage reference source, a Zener diode that is
operated with reverse voltage and which has broken down. Such a diode has a constant voltage
across it even if the current varies, and it can be used in a circuit which compares this steady
voltage with the output voltage of the chip, using this difference to control the output voltage.
n Note
The power supplies for computers and other devices that use large currents (typically
20 A or more) at low voltage levels (typically 5 V or less) are constructed differently,
using what is called a switch-mode power supply. This uses an oscillator (see later) to
Figure 2.18:
Rectification of AC using diodes. The simple half-wave action is used for demodulation
(see later), but the four-diode bridge circuit is almost universally used for AC to DC conversion
for power supplies
Figure 2.19:
A stabilized power supply, using a transformer, a diode bridge, and a stabilizer chip. The electrolytic
capacitors ensure that enough charge is stored to maintain voltage for the short intervals when the
output from the diodes approaches zero twice in each cycle

generate pulses at a high frequency, and these pulses are rectified and smoothed to
provide the output. The output voltage is also used to control the action of the oscillator
so that the output voltage remains constant even when the amount of current changes
rapidly.
n
Other Diode Types
Zener diodes, as we have seen, are used with reverse bias, making use of the breakdown that
occurs across a silicon diode when the reverse voltage is comparatively large. Breakdown
occurs at low voltages (below 6 V) when the silicon of the diode is very strongly doped (mixed)
with other elements, and such breakdown is termed Zener breakdown, from Clarence Zener
who discovered the effect. For such a true Zener diode, the reverse characteristic is as shown in
Figure 2.20(a). Another breakdown effect, avalanche breakdown, occurs in silicon with less
doping and at higher reverse voltages.
Both types of diodes are, however, known as Zener diodes and those with breakdown voltages
in the range of 4e6 V can combine both effects. The stabilization of a diode is measured by
a quantity called dynamic resistance, which can be as low as 4 U. This quantity measures how
effective the diode is in reducing small changes of voltage across it; the lower the dynamic
resistance the better the stabilization.
A typical simple circuit is illustrated in Figure 2.21. The Zener diode is connected in series
with a resistor which is used to limit the current (to avoid damaging the diode). If the supply
voltage input varies, but does not fall as low as the Zener voltage, then the current through the
diode will vary but the voltage across the diode will be almost constant.
Varactor diodes
All diodes that use a junction between two layers of silicon have a measurable capacitance
between anode and cathode terminals when the junction is reverse biased, and this capacitance
Figure 2.20:
Zener diode. The true Zener effect causes a ‘soft’ breakdown (a) at low voltages; the avalanche
effect causes a sharper turnover (b)
44 Chapter 2

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Title: A Summer's Outing, and The Old Man's Story
Author: Carter H. Harrison
Release date: September 8, 2012 [eBook #40710]
Most recently updated: October 23, 2024
Language: English
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*** START OF THE PROJECT GUTENBERG EBOOK A SUMMER'S
OUTING, AND THE OLD MAN'S STORY ***

Carter H. Harrison
A Su m m e r 's Ou t i n g
A N D
THE OLD MAN'S STORY

BY
CARTER H. HARRISON.
CHICAGO:
DIBBLE PUBLISHING CO.
1891.
COPYRIGHTED BY
DIBBLE PUBLISHING CO
1891
ALL RIGHTS RESERVED
G. M. D. LIBBY
PRINTER AND ELECTROTYPER
CHICAGO
Transcriber's Note: Minor typographical errors have
been corrected without note. Dialect spellings,
contractions and discrepancies have been retained.
The cover of this book was created by the
transcriber and is placed in the public domain.
PREFACE.

A Summer's Outing comprises letters hastily written while the
writer was on the wing. Being printed in the Chicago Tribune they
were favorably received by many friends, who have urged their
being published in book form, as a thing now needed by would-be
tourists to the Yellowstone National Park and to Alaska. To this end
they were revised and somewhat enlarged. If the little book be of
little value, the apology is offered that it will be, too, of little cost.
The Old Man's Story is thrown in as filling between two covers, and
need not be read except by those who find an idle hour hard to
dispose of.
Carter H. Harrison.
231 Ashland Boulevard,
Chicago, May 6th, 1891.
TABLE OF CONTENTS.
INTRODUCTION.
The Writer Indulges in Fancies 9
LETTER I.
A Run Through Pretty Wisconsin and Minnesota — Beautiful
St. Paul — Jealousy Between Twin Cities — An Indignant
St. Paul Democrat and a Careless Seattle Man — Dakota
and the Dirty Missouri River — A Dissertation on Waste
of Land and Destruction of Trees — The Bad Lands — The
15

Yellowstone River — Gateway to National Park and its
Guardian Eagle
LETTER II.
The National Park, The Wonderland of the Globe — The
Home of the Evil One — Steam Vents — Geysers — The
Grotto — The Giant — The Bee-Hive — The Castle and Old
Faithful in the Upper Geyser Basin 27
LETTER III.
Mammoth Hot Springs — A Wonderful Formation — The White
Elephant — A Theory Accounting for the Hot Springs and
Geysers — Mud Geysers — Marvelous Colorings of Some
Pools 45
LETTER IV.
How to do the Park — Hotels and Vehicles — My Innocents —
Charming Scenery — Natural Meadows — Wild Animals —
Beautiful Flowers — Debts to the Devil — Camp Life and
Fishing — Wonderful Canyon — Painted Rocks — Glorious
Waterfalls — Nature Grotesque and Beautiful 59
LETTER V.
We Leave the Park Satisfied — Helena — Its Gold Bearing
Foundations — Broadwater — A Magnificent Natatorium
— A Wild Ride Through Town — Crossing the Rockies —
Spokane — A Busy Town — Midnight Picnic — Fine
Agricultural Country — Sage Bush a Blessing —
Picturesque Run Over the Cascades — Acres of Malt
Liquors — Tacoma — A Startling Vision of Mt. Renier
(Tacoma) — Washington, a Great State 82

LETTER VI.
Thriving and Picturesque Seattle — Two Curious Meetings —
Victoria and its Flowers — Esquimault and the Warspite
— Two Broken Hearted Girls — Charming Sail on the
Island Sea — Picturesque Mountains — Growth of Alaska
— Whales and their Sports — Native Alaskans — Their
Homes, Habits, Food, Feasts and Wild Music — Baskets
and Blankets — Salmon Fisheries — Mines and Dogs 102
LETTER VII.
Steaming up the Ice-Packed Fiords and Channels of the Arctic
Country owned by Uncle Sam — Salmon Canneries —
Canoe Building by Natives — Ascent of the Muir Glacier,
an Ice Cliff 300 Feet High — Fantastic Ice Formations at
Takou — Summer and Winter Climates — Impudent Crows
and Oratorical Ravens 134
LETTER VIII.
Vancouver — A Picturesque, Growing City — A Run over the
Canadian Pacific — Magnificent Scenery met with from
the Start — A Glorious Ride — Fraser River Glutted with
Salmon — A Never-Tiring View from Glacier House, Four
Thousand Feet above the Sea — Rugged, Precipitous
Grandeur of the Selkirks and Rockies — Natural Beauties
of Banff — Reflections at the Soo. 162
CHAPTER IX.
The St. Mary's River — Charming Scenery — The Locality for
Summer Homes — An Episode — Mackinaw — Grand
Rapids, a Beautiful City 196

PART II.
THE OLD MAN'S STORY.
The Secret of the Big Rock 203
LIST OF ILLUSTRATIONS.
Carter H. Harrison, (Frontispiece.)
Terrace, Mammoth Hot Springs Page 16
The Giant, Upper Geyser Basin 32
Jupiter Terrace, Mammoth Hot Springs 48
Map Illustrating Geyser Actions 54
The Grotto, Upper Geyser Basin 64
The Biscuit Bowl, Upper Basin 80
Old Faithful 90
Grand Canyon 112
INTRODUCTION.
THE WRITER INDULGES IN FANCIES.

The summer outing is a fad—a necessity of fashion. Reigning beauty
bares its brow on ocean waves and climbs mountain heights,
courting sun-kisses. Jaunty sailor hats and narrow visored caps are
donned, that the amber burning of the summer's excursion may be
displayed at early assemblies of heraldic Four Hundred. Anglo-mania
has taught at least one good lesson—that the russet cheek of
romping health is more kiss-tempting than the rose-in-cream of
beauty lolling on downy cushions. Elite closes its massive doors and
draws down front window shades; Paterfamilias sweats in his
struggle to force a balance to the credit side, and mothers and
daughters sit at back windows in glare of sunlight, wooing sun-
beams, while notices of Out of town are already placarded on front
stoops.
The summer outing is urged by honest doctors, with the admission
that change of air and scene is oftentimes worth more than all the
nostrums doled out over apothecaries' counters. Motion is nature's
first inexorable law. A tiny drop of water is pressed between two
plates of glass, apparently rendering the slightest motion impossible.
The microscope fills it with scores or hundreds of beings full of life
and energy, disporting in pleasure or waging deadly battle. Around
us and about us nothing is still. The grasses grow in refreshing
green and spring beneath the feet, but ere the wane of day, wither
and crackle under the tread. Flowers bloom in beauty and within the
hour fade in ugliness. The rock ribs of earth expand and contract
under tidal commands of sun and moon, and continents lift from, or
are sinking beneath briny oceans.
The gleaming sun, so rounded in glowing calmness as he gently
circles across the vaulted sky, is a raging mass of countless millions
boiling, dashing, burning jets, in any one of which fiery Vesuvius
would be lost as a dim spark. Myriads of starry spheres flecking the
midnight sky, are mighty suns tortured by inconceivable convulsions.
Far off beyond them the telescopic lens dips up from limitless space

countless suns, all boiling, roaring and raging in unending,
monstrous motion.
Motion evolves change. Change goes on everywhere, declares
science! Change, cries orthodoxy, is universal save in One—the
everlasting, unchangeable maker of all things! Orthodoxy tells us
that man—man the soul—, was made in God's image and was by
him pronounced good. The good in God's eye must be perfect. We
know that man—the soul man—grows—the perfect therefore grows
and perfection becomes more perfect. A Paradox! So is that
mathematical truth that two parallel lines drawn towards infinity,
meet.
The deathless soul emanates from God. Is the question irreverent?
May not the Eternal who started then and keeps all things moving
and growing—may not He grow in perfection? May not the
Omnipotent become more potent, the Omniscient wiser? Being given
to digression, I give this in advance to save the reader one later on.
In obedience to fashion's and nature's law, I would put myself in
motion and would seek change. I will take an outing in this
summer of A.D. 1890.
My daughter, a school girl, will go with me. The old and those
growing old, should attach to themselves the young. Old tree trunks
in tropical climes wrap themselves in thrifty growing vines. The
green mantle wards off the sun's hot rays, and prevents to some
extent too rapid evaporation. Gray-haired grandfathers oftentimes
delight to promenade with toddling grandchildren. This is good for
momentary divertissement, but for steady regimen it is a mistake.
Callow childhood furnishes not to the old, proper companionship.
The unfledged but intense vitality of the one may sap the slow-
running current of the other, and reduce it to the lower level—to
second childhood. Age should tie to itself ripening youth. Then heart

and springtide is absorbed by the older, and ripe experience given to
the younger in exchange.
We resolve to do the Yellowstone National Park, by way of the
Northern Pacific Railroad, thence onward to Puget Sound and Alaska
to return by the Canadian Pacific. We hope for health, pleasure and
brain food. I shall write of our goings and comings, that my friends
at home may through our eyes feel that they are voyaging with us.
A beautiful or grand scene is doubly enjoyed when one feels he may
through a letter have hundreds see what he sees and as he sees.
They become his companions and hold sweet communion with him,
though thousands of miles may lie between them. This is sympathy,
and sympathy makes the joy of life. The tete-a-tete between lovers
beneath the milk-white thorn that scents the evening gale, is
delicious. But not more sweet than the communion between the
orator and the mighty audience which he sways and bends at will.
He holds a tete-a-tete with each of his listeners.
Byron swore he loved not the world, nor the world him. The bard
was self-deceived. He wrote that he might win the sympathy of
millions. Bayard Taylor told the writer once that he wrote from an
irresistible impulse. His warm, generous nature yearned for the
sympathy of a reading world. I shall write that a few hundred may
see through my eyes—may feel when my heart beats, and for a few
brief hours may be in sympathy with me. Some one possibly may
sneer Cacoethes Scribendi. Catch the retort, Honi soit qui Mal-y-
pense.

LETTER I.
A RUN THROUGH PRETTY WISCONSIN AND MINNESOTA. BEAUTIFUL ST. PAUL.
JEALOUSY BETWEEN TWIN CITIES. AN INDIGNANT ST. PAUL DEMOCRAT
AND A CARELESS SEATTLE MAN. DAKOTA AND THE DIRTY MISSOURI RIVER.
A DISSERTATION ON WASTE OF LAND AND DESTRUCTION OF TREES. THE
BAD LANDS. THE YELLOWSTONE RIVER. GATEWAY TO NATIONAL PARK AND
ITS GUARDIAN EAGLE.
Mammoth Hot Springs, July 17, 1890.
We left Chicago by the Wisconsin Central Railroad for St. Paul. From
the beginning the run was interesting, especially to one who
remembers what the country was thirty-five years ago—an almost
flat prairie of tangled grass, in which the water was held as in a
morass, promising but little to the ambitious earth-tiller. I recall a
remark of Senator Douglas when the future of our flat prairies was
being discussed in my presence thirty-five years ago: People do not
realize that the drainage problem is being now daily solved. The
leader of a herd of cattle browsing the prairies, is an engineer, and
his followers faithful laborers in making ditches. When going to and
from their grazing grounds, they march in line and tread down paths
which make no mean drains. The cattle of Illinois are annually lifting
millions of acres out of the swamp into good arable lands.
As soon as the Des Plaines was crossed, good farms began, and
comfortable farm houses were always in sight; oats bent and waved
in light green, and corn stood sturdy in emerald, where a third of a
century ago, even in July, a pedestrian was compelled to step from
ant-hill to ant-hill to keep his ankles dry. Copses of young wood
relieved the monotony of too much flatness, and in a few hours after
our start, pretty lakes shimmered in the sinking sun light, and
sweetly homelike villas were ever in view. We crossed the Wisconsin

line, and hill and vale or gentle undulations with wooded heights and
flowing streams, and villages and saw mills enlivened the journey.
TERRACES AT MAMMOTH HOT SPRINGS. (SEE PAGE 16.)
In the distant future when population shall become abundant, and
tasteful homesteads shall replace somewhat speculative shanties,
few countries of the world will be more pleasingly rural than
southern and middle Wisconsin.
Books should be carried by the tourist in his trunk, and newspapers
should be religiously discarded throughout the run to St. Paul. The
country traversed opens many a pleasing page during the summer
months, and glowing pictures are spread before him on nature's
living canvass. He unfortunately loses much when the curtain of
night is drawn over God's own impartial book: the book which never
misleads if carefully read and studiously digested.
At St. Paul we had some hours to ride about the pretty town, before
boarding the Northern Pacific railroad for our long journey to Puget's
Sound. This great road has the singular characteristic of having
double termini at each end, and between each of the twins there

exists a feud rarely found except between cities engaged in actual
war with each other.
Athens and Sparta hated each other not as do St. Paul and
Minneapolis. Just now, owing to the taking of the census, there is
blood in the eye of every St. Paulite. An elderly gentleman
introduced himself to me the other day at the station. After a while
he said: It is a —— shame the way the United States is treating St.
Paul. I am a Democrat, sir, and can stand a little stuffing of the
ballot-box, but I draw the line there. I can't stand the stuffing of the
census. We are willing to concede to Minneapolis 10,000 more
population than we have, but Harrison ought to be turned out of
office for running it up to 40,000. It is a fraud, sir—a miserable
Republican fraud. We will be revenged, sir, and will show our teeth
next fall and don't you forget it. I sympathized with him and felt like
marching to Washington at once to send my cousin Ben back to
Hoosierdom.
In the National Park I saw at four different hotels the names of Mr.
—— Mrs. —— and two little blanks. There was a bracket after the
names, but the writer had evidently forgotten to write in the
address. The name preceding his on the first book was from Boston.
At the next place the preceding person was from New York, and
again from some other city. The fourth day at dinner I was
introduced to the head of the family. He was from Seattle. I asked
him why it was he had not put in his address, declaring I would tell
it on him at Tacoma. Good Heavens! he exclaimed, have I done
that? He rushed back to the register and wrote Seattle as big as a
John Hancock. The next time we met in a crowd, I twitted him about
the thing. He then declared he must have left out the address
instinctively from a natural aversion to being known to come from
any spot so close to Tacoma. Considerable jealousy of St. Paul on
the part of her twin city is natural, for it is a beautiful town. Its
residences on the hills are very fine, and their locations lovely
beyond those of all but few cities. The entire town was very clean,

and in the hill portion bright and cheerful. The residences are
generally surrounded by considerable grounds, filled with trees and
shrubbery, in much variety and in luxuriant growth. The young girl
with me fell so completely in love with the clean, pretty place, that
she declared, if she ever got married it would be to a St. Paul man.
The run through Minnesota is as if through a great park. Everything
is green and bright. Copse, meadow and field are as fresh as a May
morning. The natural location of frequent wooded clumps, of prairie
openings and of lakes, could hardly be improved by a landscape
engineer. We passed the great wheat fields of Dakota at night, but I
thought there was far less of barren plain and alkali patches as we
approached the Missouri river, than I saw there seven years ago.
How different the feelings with which we approached the Missouri
from those experienced as we drew near the Mississippi! One cannot
get up a feeling of respect for the tortuous, treacherous, muddy,
long and snake-like ditch. One takes off his hat to the Father of
Waters, but feels like kicking, if he had a place to kick, this lengthy,
nasty thing. No one can see any real use for it, except as a tributary
to and feeder of the Mississippi. It has not and never had a placid
infancy. Several of its upper feeders are beautiful, clear, rapid,
purling streams. But some of them apparently without rhyme or
reason suddenly become flowing mud. One dashes on a train along
one and wishes he could alight to cast a fly for a speckled beauty.
The road takes a turn around a mountain spur, and lo! the crystal
stream has become liquid mud, to prepare itself, I suppose, for the
mucky thing it will soon join. Possibly and probably, these
transformations are owing to a miner's camp and a placer washing
on the other side of the spur.
North Dakota has not become settled along the railroad, after
quitting the great wheat belt, as I expected. Farms are very
scattered, and when seen are small and wear an air of neglect. Yet
the native plains are cheerful looking and roll off in green

undulations. The Forest Commissioners, if there be any, must find
some more hardy species of trees than those now used to enable
them to grow brakes for warding off the winds and blizzards. The
railroad people have planted many trees, but they do not thrive.
They seem alive about the roots, but dead after reaching one or two
feet. Possibly a blanket of snow lies about the roots in winter and
protects them; but the alternation of cold and hot winds apparently
kills the sap as it rises higher up. Government should inaugurate a
thorough system of arboriculture, inviting and encouraging a real
science.
The Socialists say the Nation should own the land. To a certain
degree the Socialists are right. The fountain of land ownership is in
the Government. It should maintain such ownership to a certain
extent throughout all time. The earth is the Lord's and the fullness
thereof. Government is and should be the lord of the domain, and
should never part with such control as may prevent private owners
from destroying the land which is to be the heritage of the people to
the latest generation. It should forbid and prevent a waste of land.
To this end it should force the husbanding of all resources for the
improvement of that which is to support the people for all time. No
private owner should be allowed to destroy wantonly that which
comes from mother earth. What comes from the bosom of the land,
and is not essential to feed and maintain the cultivator, should be
given back to it. A man should be fined who burns manure. Man
should not cut timber to such an extent as to reduce a necessary
rainfall. Commissioners should determine from scientific data, how
much of forest is necessary in fixed districts of the country, and
when so determined no one should be permitted to cut a tree
without replacing it by a young one. In the Old World millions of
acres are now worthless which once supported teeming populations;
all because they have been denuded of trees. Nearly all European
countries as well as India are now, and have been for some years,
earnestly endeavoring to check this evil. Commissioners of Forestry,

earnest and educated men, have been appointed. Schools of
Forestry are fostered by the state. The betterment has been so
marked, that the ordinary pleasure seeking traveler sees a wonderful
change between visits separated by twenty or thirty years. America
has countless millions of acres scarcely capable of supporting a
human being, which could be made to wave in cereals or grow fat in
edible roots, if only trees were grown to induce a somewhat regular
rainfall.
The arid plains of the Great West have the richest of known soils, if
a little human sweat mixed with water in sufficient quantity could be
kneaded into it. Government as the lord paramount of its domain,
should force the growing of trees and should prevent the destruction
of timber wherever the same is necessary to keep up or improve the
land. It has parted with the title to the soil, but still retains the
power to use it for its own support. It levies and collects taxes from
lands as the paramount owner. The same power exists to prevent
the waste of that from which its taxes spring or through which its
people may live.
No one is a man, says the Arab maxim, until he has planted a
tree, dug a well, and grown a boy. The nation is an aggregation of
men and should follow the maxim. The statesman who devises a
good system of taxation is entitled to the praises of all men, but he
is but a pigmy to the man who turns sterile deserts into places of
plenty, or who make many blades of grass grow where now only one
springs up. I am ready to bow down before the man who will
maintain and improve the soil of our Eastern States, or will shower
over the West a copious rainfall.
Bismark was disappointing. It has not improved as could have been
expected since we helped to lay the corner-stone of its Capitol seven
years ago.
BAD LANDS OR MAUVAISES TERRES.

The bad lands are as God-forsaken in appearance as they were
years since. There the very earth has been burned and the Evil One
seems to have set his foot-print on every rod. Men do live in them,
but more blessed is he who dies in genial surroundings! What a hold
upon us has the love of life! So short and such a bauble! How
worthless when robbed, as it must be in this bleak tract, of every
concomitant of the joyful! Only the All-powerful can reclaim the soil
of the bad lands, and not until a cataclysm has carried it 1,000
fathoms beneath the sea, will it be fitted for sunlight and ready to
support life. It has been burned up with the coals and lignites which
underlaid the surface. After striking the Yellowstone Valley the ride
westward becomes pretty. The mountains are bold, with fine
outlines, often lifting in picturesque precipices from the water's
edge. Great strata of coal are frequently seen stretching in level
parallel lines for considerable distances. Snow appears in seams and
gorges on the loftiest heights. While not offering as grand displays
as are seen in one or two points of other across-the-continent roads,
the Northern Pacific presents more varied scenery, and far more that
is pleasing and restful to the eye, than any other except the
Canadian Pacific.
To most travelers much of the scenery of the Northern Pacific until
Helena is reached is monotonous. But to one disposed to be a
student of nature and a lover of its varied forms, many instructive
lessons can be conned from the car window, and many pleasing
pictures hastily enjoyed. The Yellowstone, along whose banks the
road runs for three hundred and fifty miles, is a cheerful stream.
When first reached it is muddy, but after the mouths of one or two
large affluents have been passed it becomes clear and limpid. Its
flow is almost constantly rapid and turbulent. But few still reaches
are seen, and these are rarely over a mile or so in length. On one or
the other bank considerable mountains lift from the water's edge, in
lofty, clear-cut precipices. The upper slopes have but few trees and
rarely any clumps or masses, but offer much variety in earth

coloring. Light brown, sometimes deepening into chocolate, is the
dominant tone. There are frequent stretches of yellow, here and
there flecked with patches or bands of venetian red. This latter
sometimes takes a tint so bright as to merit being called vermilion.
At Livingston, a thousand and odd miles from St. Paul, we left the
Northern Pacific, and by a narrow-gauge road continued up the
Yellowstone, fifty-one miles to Cinnabar; thence by Park coaches,
wagonettes and surreys, eight miles along the wildly rushing
Gardner river, and through a narrow defile hemmed in by lofty
precipices beneath frowning crags—the gateway to the park—to the
Mammoth Hot Springs. Near the gateway on a lofty pinnacled rock,
so slender as at first to be mistaken for the trunk of a huge tree, sat
an eagle upon its eyrie, keeping watch and ward over the entrance
to the people's pleasure ground. The bird's nest is built of loose
sticks laid upon the rocky point, which is not broader than a good-
sized tree stump. How it withstands the dash of storms, which often
rage through the narrow pass, is a marvel. Yet it has been there for
many years, and each year sends forth its young brood. I regret to
say this eagle is not the genuine American screamer, which so
grandly spreads its wings upon the daddy's dollar, but is the great
white-headed fish-hawk. He is easily mistaken for the bald eagle, but
is smaller and a somewhat sociable bird, building his home near by
those of others of his species. The true eagle is sullen and solitary,
and chooses his eyrie many miles removed from his fellows. Indeed
he spurns all fellowship with his kind.
All tourists delight to look at the Devils Slide in the Gardner
canyon. It is from five to six hundred feet high, a few feet broad,
between thin slate dykes, and as smooth as a toboggan way. As
there is no record that the father of lies was acquainted with sand
paper, there is a peculiar pleasure in imagining the grinding away of
the seat of his trousers, while he was polishing down his coaching
slide. In spite of what the preachers say, there is no doubt that man,

woman and child hate the devil, and are delighted by any evidence
of annoyance to him.

LETTER II.
THE NATIONAL PARK, THE WONDERLAND OF THE GLOBE. THE HOME OF THE
EVIL ONE. STEAM VENTS. GEYSERS. THE GROTTO. THE GIANT. THE BEE
HIVE. THE CASTLE AND OLD FAITHFUL IN THE UPPER GEYSER BASIN.
Grand Canyon,
Yellowstone National Park, July 22.
American dudes of both sexes wandering about the world have been
sorely perplexed because Uncle Sam has had no huge ships of war
with which to display his grandeur in foreign ports, and no
embassadorial residences in which Yankee heels may air themselves
to advantage. When foreigners have made allusion to our poverty in
this regard, and their own wealth of splendor, we have been forced
to fall back upon the Yankee's retort, Yes; but you hain't got no
Niagary. Luckily but few of those who taunted us were aware that
Niagara was simply located in the United States but did not belong
to it. But now we can throw back at the effete denizens of other
lands the wonderland of the globe,—The Yellowstone National Park
—in which there is more of the marvelous sports of nature than
exists in the entire outer world besides. We can tell them of these
wonders, and can then say that these marvels are the Nation's, and
that this park of over 3,500 square miles is maintained by the Nation
for the people, for their amusement and recreation. It is to be
regretted that more of the surplus which has been lying idle in the
treasury vaults has not been expended to enable the people to
better enjoy their wealth of wonders. The people may read of their
treasures; they may see folios of illustrations, but no one can
comprehend them without seeing them; no pen pictures can bring
them before the eye of one who has not been here; no photograph
can display their forms and then dye them in their wondrous colors;

no painter can spread them upon canvas, for he would at once be
put down as an artistic liar. The simple truth is an exaggeration, and
a precise copy is a distortion of nature's molds.
THE EVIL SPIRIT'S ABODE.
No wonder the Indians have given this section of the country a wide
berth, for well might they believe it the home of the evil spirit. One
of them straying here might wander for days and never mount an
elevated point without being able to count scores of columns of
white steam lifting above the trees from different points of the
forest, telling him of the wigwams of the evil one. If he stole along
the valleys, he would come upon pools of water of crystal clearness
tempting in appearance to the thirsty; some of them not larger than
the blanket which covered his shoulders, others so large that the
tepees of half his tribe would not cover their area; some mere
jagged holes in the rock, others with rims a foot or so in height, and
as regular as his pipe of peace. Here are some a few inches or a few
feet in depth, with bottoms and sides painted in rainbow tints; there
are others with deep sunken walls embossed and tufted, and dyed
with the colors of the setting sun, and with dark throats so deep that
they seem to be yawning from fathomless depths. Here they are as
placid as the eye of the papoose hanging at the squaw mother's
back. Our Indian pauses at the painted brink of one, dips his hand
into the tempting fluid—jerks it back quickly, but perhaps not before
it is scalded. There they boil up one, two, three or more feet and
appear as though they would pour out a flood from below, but not a
drop passes over the rim of the pool. The boiling motion is from
volumes of steam working its way through the waters from the
bowels of the earth and spreading upon the breeze. Boiling water
elsewhere wastes itself away, but these pools boil and boil from year
to year, and scarcely vary perceptibly in height. Our untutored tourist
turns his eye upon the mountain bordering the valley, whose sides
are so encrusted with geyserite deposit that it appears to have been

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