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RALPH G,
HUDSON




AN

INTRODUCTION TO
ELECTRONICS x

by Ralph G. Hudson

The enormous potentialities of the

\ relatively new science of electronics ^

have only begun to be used. It has ^



given us radio, sound movies, fac-
simile reproduction, television. It has
produced miracles in the use of radar,

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the radio compass, and other war
Such instruments as the









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San Francisco, California
2006



From the collection of the

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AN INTRODUCTION TO ELECTRONICS



THE MACMILLAN COMPANY

NEW YORK - BOSTON CHICAGO DALLAS
ATLANTA SAN FRANCISCO

MACMILLAN AND CO., LIMITED

LONDON BOMBAY CALCUTTA MADRAS
MELBOURNE

THE MACMILLAN COMPANY
OF CANADA, LIMITED

TORONTO




Broadcasting Company WNAX

The tallest mast-type antenna in the United States is located at Yankton,
South Dakota, and has an over-all height of 927 feet above the ground. Its total
weight, including the down pull of six guy wires, is 190 tons which is supported by a
single porcelain insulator, 30 inches in diameter and 36 inches high. For efficient
radiation the height is 53 per cent of the wave length of the broadcasting frequency,
which is 570 kilocycles per second.



V



AN INTRODUCTION
TO ELECTRONICS



RALPH G. HUDSON

PROFESSOR OF ELECTRICAL ENGINEERING
AND CHAIRMAN OF THE COURSES IN GENERAL
SCIENCE AND GENERAL ENGINEERING AT THE
MASSACHUSETTS INSTITUTE OF TECHNOLOGY



THE MACMILLAN COMPANY

NEW YORK 1946



COPYRIGHT, 1945, BY THE MACMILLAN COMPANY

All rights reserved no part of this book may be reproduced in
any form without permission in writing from the publisher, except
by a reviewer who wishes to quote brief passages in connection
with a review written for inclusion in magazine or newspaper.

Reprinted May, 1946



PRINTED IN THE UNITED STATES OF AMERICA



PREFACE



Electronics is that branch of science which describes the prop-
erties and control of electrons and other rudimentary particles
which, in correlation with energy, constitute matter. Energy is the
agency by which matter is united, disintegrated, or displaced, and
appears in many diverse forms, such as mechanical, chemical,
thermal, electrical, magnetic, and atomic energy. Matter is the
substance of which any physical material is composed. The science
might have been called "protonics" or "neutronics" with reference
to other rudimentary particles but "electronics" was chosen to
emphasize the prominence of the most active ingredient of matter.

Electronics has given man a better understanding of the hidden
resources of nature. The discovery of 'the electron would still have
attained enormous importance if no application of its properties
had been made to radio communication, sound-motion pictures,
or television. The science of electronics has opened a vista of
applications which appear to be limitless and beyond our imagina-
tion. We have seen various applications which lend comfort,
enlightenment, and amusement to mankind but these uses may
pale into insignificance compared with the development of new
materials and new sources of food and energy. The purpose in part
of this book is to acquaint the layman with some of the outstanding
new concepts of the physical world together with the implications
of their probable effect upon his manner of living.

The understanding of any of the special or advanced sciences is
greatly simplified by a preliminary study of physics, chemistry,
and mathematics. Although such preparation gives the student a
general knowledge of the basic principles of the fundamental
sciences, a consequent attainment of greater importance is the
acquirement of a scientific vocabulary. The author is always
skeptical of the reason when a man says he "hasn't a scientific
mind." It is more probable that he has not developed the habit
of referring steadily to a comprehensive dictionary for the meaning
of unfamiliar words. Beneficial reading of scientific literature



vi PREFACE

requires not only an accurate understanding of scientific words but
of common words as well.

Another handicap to accurate reading is the ascription of wrong
meanings to important words. Thereafter the subsequent reading
cannot make sense. Students of all grades often fail examinations
not because they do not know the answers but because they do not
know the exact meaning of the questions. The reason why many
persons get nothing out of a legal decision, a doctor's report, or
even an income-tax blank is because they do not know the meaning
of the words. The first requirement for an adequate understanding
of electronics without previous contact with the fundamental
sciences is the possession and constant use of an up-to-date dic-
tionary.

The lay reader will also experience some difficulty at first in
comprehending some of the astronomical numbers that pervade
the literature of electronics. For example, it is stated later in the
text that "in the normal hydrogen atom the electron revolves about
the proton nearly 10 16 times in a second." The notation 10 16 means
one multiplied by 10, 16 times; that is, one with 16 zeros after it, or
10,000,000,000,000,000. When the reader becomes accustomed
to this notation he will at once recognize 10 2 as 100, 10 5 as 100,000,
10 9 as 1,000,000,000, and so on. Electronic literature also contains
exceedingly small numbers. Referring to the proton the text states
that "its diameter is about 10~ 16 centimeter," where 10~ 16 means
one divided by one multiplied by 10, 16 times; that is, one with
161 zeros before it, to the right of the decimal point, or
0.000,000,000,000,000,1. Expressed as a fraction this number
would be 1/10,000,000,000,000,000. In the simplified notation
the reader will soon recognize 10~ 2 as 0.01, 10~ 5 as 0.000,01, and
1(T 9 as 0.000,000,001.

Aside from the above notation associated with large and small
numbers the book contains practically no mathematics and assumes
no previous study of physics or chemistry. In no instance have the
difficult features of the evolution of electronics been neglected.
Simple and complex features have all been included so that the
reader will not feel that he has been let down. Most of the current
popular literature on the subject tells what electronics "can" or
"may do." In this exposition emphasis is placed not only on "can"
or "may do" but on "how" and "why." Unless the reader has had



PREFACE v ii

considerable experience in reading scientific books he must not
expect to read the book as he would a newspaper or a novel. He
must read it slowly and perhaps several times. As the subject
becomes clearer and clearer he will appreciate what Charles
Kingsley, a minister, poet, and novelist, meant when he said "For
science is ... like virtue, its own exceeding great reward." Elec-
tronics will then become an intimate part of the reader's thought
and experience.

It may also determine his life work. Vast industries have already
been established to construct and operate electronic devices. A
large part of the routine work in many research laboratories is
dedicated to a study of electronic principles and their applications.
Out of this research, industries now unknown may arise at any
moment. Financiers must have sufficient knowledge of electronic
fundamentals to decide whether each new project will succeed and
deserve their support.

Many of these industries must have advertising personnel who
will be able to write convincing copy. The doctor, the dentist,
and the lawyer will discover that electronics to him should not be
a strange science. Although it ranks first in the domain of the
physicist, the chemist, and the electrical engineer, electronics has
already become an essential science in various branches of civil
engineering, mechanical engineering, metallurgy, biological
engineering, chemical engineering, geophysics, marine engineering,
and aeronautical engineering. Unquestionably electronics will
not only establish its importance among most of the professions but
also in the life of every man.

R. G. HUDSON

Cambridge, Massachusetts



All capitalized names of apparatus mentioned in this book are trade
names.



TABLE OF CONTENTS



I. THE CONSTITUTION OF MATTER 1

The Cathode-ray Tube Discovery of the Electron The
Hydrogen Atom The Bohr Model of the Atom The He-
lium Atom The Spectroscope The Electron Orbits
The Bohr Model in General The Ninety-two Elements
Atomic Numbers and Isotopes Relation between Mass and
Energy The Wilson Cloud Chamber Cosmic Rays,
Positrons, and Mesotrons Balance of Energy Requires a
Neutrino Disintegration of the Elements The Photon
Electronics Comes to the Aid of Alchemy The Electron- Volt

The Cyclotron Other Sources of High-energy Particles
Transmutation Achieved Utilization of Atomic Energy.

II. THE FLOW OF ELECTRICITY 21

The Electric Current The States of Matter Conduction
in Gases Conduction in Nonmetallic Liquids Conduction
in Solids Conduction in a Vacuum.

III. RADIO COMMUNICATION 29

Thermionic Emission Construction and Operation of the
Diode The Function of the Grid in the Triode Radiation
of Energy Reception of the Radiated Energy Amplitude
Modulation More Amplification Tetrodes and Pentodes

Tuning In Oscillators Frequency Modulation.

IV. REPRODUCTION OF SOUND AND PICTURE 45

Photoelectric Emission The Phototube Proof of the
Quantum Theory Sound Reproduction on Film Trans-
mission of Still Pictures Television.

V. MODERN SOURCES OF LIGHT 59

Radiation and Vision Sources of Visible Radiation Pro-
duction of Light by Incandescent Solids Production of
Light by Gaseous Conduction.

ix



T TABLE OF CONTENTS

VI. MORE POWER TO THE ELECTRON 69

From Watts to Kilowatts Applications of Direct Current
Rectifiers of Moderate Currents Grid-controlled Rectifiers
The Glass Mercury Arc Rectifier The Steel-tank Mercury
Arc Rectifier Rectox and Selenium Rectifiers Photo-
voltaic Cells.

VII. DIVERSE APPLICATIONS OF ELECTRONICS 76

The Electron Microscope The Radio Compass The
Radiosonde Medical Electronics But That Is Not All.

CONVERSION FACTORS 94

INDEX 95



AN INTRODUCTION TO ELECTRONICS



CHAPTER I
THE CONSTITUTION OF MATTER



The Cathode-ray Tube

When a voltage of sufficient magnitude from a battery or a
generator is applied between the metal terminals of a partially evac-
uated glass tube, as shown in Fig. 1, a ray of light is established



Cathode





Fig. 1. A luminous ray is produced within ^a glass tube containing a low-
pressure gas when a high voltage is impressed between its terminals

between the negative terminal (the cathode) and the positive ter-
minal (the anode). Although the luminous intensity of the ray is
not high, this tube with certain modifications is nevertheless similar
to the modern fluorescent lamp. A screen of any shape placed
within the tube perpendicular to the ray produces a shadow of the
same shape on the anode, thus indicating that something flowing
within the tube from the cathode to the anode (and not the other
way) is intercepted by the screen. The source of the ray being the
cathode the tube is called a "cathode-ray" tube.




Fig. 2. Construction of the cathode-ray tube used with additions in a
television receiver

In another type of construction, as shown in Fig. 2, the anode
with a small hole drilled through its center is located a short dis-
tance from the cathode. With a voltage of at least 300 volts im-

1



4 THE CONSTITUTION OF MATTER

the inward pull of the proton. There were two serious objections
to this theory. In the first place, there are an infinite number

^- ^ x of radial distances and velocities

/ N \ that the electron might take

/ \ which would provide the neces-

sary compensation of forces. In



El the second place, it had heretofore



\ r been assumed that a revolving

electron would steadily radiate






energy and, in consequence, lose
Fig. 3. A rudimentary model of the velocity and fall back into the
hydrogen atom proton.

The Bohr Model of the Atom

Evidence has accumulated in recent years that energy itself is
not divisible into any number of parts, but that the division is lim-
ited to certain portions, under the prescribed circumstances, called
" quanta." A quantum of energy is not a fixed quantity like the
charge on an electron or a proton but varies with the conditions to
which it must react. Applying this principle to the hydrogen atom,
Dr. Niels Bohr suggested that the electron may revolve about the
proton, as shown in Fig. 3, at definite radial distances and velocities
but that it takes a certain indivisible quantum of energy to make
it spiral from one orbit to another. If an insufficient amount of
energy is received or lost it must remain where it is.

According to this theory, in the normal hydrogen atom the elec-
tron revolves about the proton nearly 10 16 times in a second at a
radial distance of about 10~ 8 centimeter and with a velocity of
about 4000 miles per second. The system of units is scrambled be-
cause it is believed that the reader may visualize miles per second
better than centimeters, meters, or kilometers per second. A model
of the hydrogen atom, or any other atom, may not be drawn to
scale. If the electron is made sufficiently large to be seen, the pro-
ton would be invisible and off the page. Other theories of atomic
structure have been proposed at various times but at the moment
the Bohr model has proved quite satisfactory in presenting the
simplest aspect of the picture. Greater refinement of atomic struc-
ture indicates that an electron in motion must be regarded not only
as a particle but also as a wave.




Allen B. Dumont Laboratories, Inc.

A cathode-ray oscillograph which traces on a fluorescent screen the instan-
taneous variations of an electric current. The picture shows a sinusoidal alter-
nating current.



THE SPECTROSCOPE 5

The Helium Atom

The next heavier atom among the elements is helium which
weighs about four times as much as the hydrogen atom. To give
the nucleus the proper mass it was first assumed that it contains
four protons and two electrons, surrounded by two revolving
electrons. Subsequent bombardment of helium and various other
gases with high-velocity particles has shown that when a nucleus



Neutron




Proton



Electron I



Neutron



Fig. 4. The constituents of the helium atom

is disrupted it often throws out a particle which has no charge and
has a mass slightly greater than that of a proton. This particle
has appeared in many nuclear reactions and is called a "neutron."
It is now definitely established that the helium nucleus contains
two protons and two neutrons, which combined account for almost
the entire weight of the atom. This model of the helium atom (not
to scale) is shown in Fig. 4. Since all other heavier atoms have also
shown evidence of possessing neutrons in their nuclei, it is believed
that the three stable building blocks of the universe are the electron,
the proton, and the neutron.

The Spectroscope

It is not possible in this brief and nonmathematical discussion to
explain how Bohr and others have determined the nuclear and
orbital structure of the 92 elements from hydrogen with an atomic
weight of about 1 to uranium with an atomic weight of about 238.
Much of the contributory evidence has come from the spectroscope.
In this instrument a small piece of an element to be examined is
dropped into the high- temperature crater of a carbon-arc lamp
where the individual atoms of the element are activated and throw
out visible and invisible radiation of frequencies characteristic of



6 THE CONSTITUTION OF MATTER

the particular atom. This radiation is sent either through an opti-
cal prism or against an opaque grating of many thousands of
equally spaced lines. In either case a spectrogram obtained photo-
graphically or visually (for part of the spectrum) will show the va-
rious frequencies of the emitted radiant energy.

The Electron Orbits

The energy stored in the revolving electron is the least when it is
located in the innermost orbit. If activation of some sort, such as
the intense heat of a carbon arc, drives the electron into an outer
orbit, it will spiral back to an inner orbit and give out high-fre-
quency radiation during the passage. An electron moves from an
inner to an outer orbit only upon the absorption of energy from
some external source. This energy is radiated wholly or partly al-
most immediately when the electron falls back to an inner orbit,
and upon arrival at an inner orbit all radiation ceases. As shown
in a later chapter practically all sources of light operate on this
principle. The amount of energy radiated when an electron spirals
inward equals 6.55 X 10~ 27 times the frequency of the radiant en-
ergy. Since the spectrograph indicates the energy differences
between characteristic orbits for various atoms it is possible with
other information to determine the number and location of the
orbits of any atom

The Bohr Model in General

Many attempts have been made to make models or draw pic-
tures showing the distribution of the orbital electrons in the various
atoms. In an early model (Fig. 5 a) the atomic structure is repre-
sented by an arrangement of the electrons in seven concentric
shells, like the layers of an onion, in which each shell represents a
quantum level one unit less than the next outer shell. The shells
are not equally spaced but progress outward with steadily increas-
ing spaces; the shells moreover are not spheres but ellipsoids. This
model was soon superseded by a more detailed and diaphanous
structure (Fig. 5 b) containing various elliptic orbits arranged in a
symmetrical pattern about the nucleus. Each orbit, while not nec-
essarily concentric to the others, is located in one of several quan-
tum levels.

This model again proved to be too simple and restrictive to sat-



THE NINETY-TWO ELEMENTS 7

isfy the observed facts and at the moment we can draw no definite
picture of the distribution of the electrons about the nucleus. The
failure to establish a satisfactory picture does not indicate a reversal
of progress or that we know less than before about the structure of
the atom. On the contrary it means that we know more. The




(a) (b)

Fig. 5. a. The concentric-shell model of the atom. b. The symmet-
rical elliptical-orbit model of the atom

model is now described by a series of mathematical equations which
are more accurate and descriptive than a picture. Modern science
in several instances has developed explanations of physical phe-
nomena which do not suggest pictures. As yet nobody has been
able to make a model containing 1 ^ fourth dimension, but the failure
of this accomplishment does not disprove its existence. Improve-
ment in the understanding of the structure of atoms will continue
without the necessity of a picture. We may even use some of the
old ones at times because they do contain some of the character-
istics of the real structure.

The Ninety-two Elements

The table on page 9 gives the name, the symbol, the atomic
weight, and the atomic number or the number of orbital electrons
for the atoms of the 92 elements. Where there are blank spaces the
properties of that element are either unknown, or the element itself
has not been discovered or isolated. There are also indications that
two other elements may exist which are heavier than uranium, thus
making it possible that there are actually 94 elements. The atomic
weights are comparative values based upon oxygen as the standard



8 THE CONSTITUTION OF MATTER

with an atomic weight of exactly 16. If hydrogen had been taken
as the standard the atomic weight of oxygen would be 15.871.

Frequent references will be made later regarding the meaning
and interpretation of this table so that it will not appear to be just
a jumble of numbers. Every living thing, so far as we know, con-
tains carbon, and that atom contains six orbital electrons. Hence
that arrangement is a requisite of life. It will be noted that iron,
cobalt, and nickel have 26, 27, and 28 orbital electrons respectively.
These arrangements appear to be requisites for highly magnetic
materials. All the elements from bismuth through uranium are
radioactive; that is, they disintegrate steadily and change into ele-
ments with fewer orbital electrons. Let us now make a study of
the atomic weights.

Atomic Numbers and Isotopes

When we have spoken of the probable existence of 92 elements
(perhaps 94) we have meant uncombined substances which possess
unique properties and occur in nature with four possible excep-
tions, in sufficient quantity to be detected. The better understand-
ing of the constitution of matter has enabled us to discover hun-
dreds of other different atoms whose existence might otherwise
have remained unknown. Since all atoms are made of an equal
and increasing number of protons and electrons combined with
neutrons, it was difficult to explain why the table of atomic weights
on page 9 contains many gaps in their orderly sequence. The
first four elements, for example, have atomic weights as follows:
hydrogen, 1.0080; helium, 4.003; lithium, 6.940; and beryllium,
9.02. In a simple atomic evolution why were there no elements
with atomic weights of 2, 3, 5, 6, and 8? Also why were the atomic
weights not integers? According to the Bohr model a hydrogen
atom contains one proton and one electron and the oxygen atom
contains eight protons, eight neutrons (each neutron weighing
about the same as one proton), and eight electrons. Yet the oxygen
atom weighs less than 16 times that of the hydrogen atom.

An examination of the Bohr models for all the elements shows
that the number of orbital electrons, called the "atomic number,"
in any atom equals roughly (in some cases closely) one half of the
atomic weight. Aston suggested that the wide departure from this
rule in the case of lithium, for example, with an atomic weight of



THE NINETY-TWO ELEMENTS









Atomic








Atomic








Number








Number


Name


Symbol


Atomic
Weight


or Num-
ber of


Name


Symbol


Atomic
Weight


or Num-
ber of








Orbital








Orbital








Electrons








Electrons


Hydrogen


H


1.0080


1


Silver


Ag


107.880


47


Helium


He


4.003


2


Cadmium


Cd


112.41


48


Lithium


Li


6.940


3


Indium


In


114.76


49


Beryllium


Be


9.02


4


Tin


Sn


118.70


50


Boron


B


10.82


5


Antimony


Sb


121.76


51


Carbon


C


12.010


6


Tellurium


Te


127.61


52


Nitrogen


N


14.008


7


Iodine


I


126.92


53


Oxygen





16.0000


8


Xenon


Xe


131.3


54


Fluorine


F


19.00


9


Cesium


Cs


132.91


55


Neon


Ne


20.183


10


Barium


Ba


137.36


56


Sodium


Na


22.997


11


Lanthanum


La


138.92


57


Magnesium


Mg


24.32


12


Cerium


Ce


140.13


58


Aluminum


Al


26.97


13


Praseodymium


Pr


140.92


59


Silicon


Si


28.06


14


Neodymium


Nd


144.27


60


Phosphorus


P


30.98


15











61


Sulphur


S


32.06


16


Samarium


Sm


150.43


62


Chlorine


Cl


35.457


17


Europium


Eu


152.0


63


Argon


A


39.944


18


Gadolinium


Gd


156.9


64


Potassium


K


39.096


19


Terbium


Tb


159.2


65


Calcium


Ca


40.08


20


Dysprosium


Dy


162.46


66


Scandium


Sc


45.10


21


Holmium


Ho


163.5


67


Titanium


Ti


47.90


22


Erbium


Er


167.2


68


Vanadium


V


50.95


23


Thulium


Tm


169.4


69


Chromium


Cr


52.01


24


Ytterbium


Yb


173.04


70


Manganese


Mn


54.93


25


Lutecium


Lu


174.99


71


Iron


Fe


55.85


26


Hafnium


Hf


178.6


72


Cobalt


Co


58.94


27


Tantalum


Ta


180.88


73


Nickel


Ni


58.69


28


Tungsten


W


183.92


74


Copper


Cu


63.57


29


Rhenium


Re


186.31


75


Zinc


Zn


65.38


30


Osmium


Os


190.2


76


Gallium


Ga


69.72


31


Iridium


Ir


193.1


77


Germanium


Ge


72.60


32


Platinum


Pt


195.23


78


Arsenic


As


74.91


33


Gold


Au


197.2


79


Selenium


Se


78.96


34


Mercury


Hg


200.61


80


Bromine


Br


79.916


35


Thallium


Tl


204.39


81


Krypton


Kr


83.7


36


Lead


Pb


207.21


82


Rubidium


Rb


85.48


37


Bismuth


Bi


209.00


83


Strontium


Sr


87.63


38


Polonium


Po


1 3 4 5 6 7 8 9

Online LibraryRalph G. (Ralph Gorton) HudsonAn introduction to electronics → online text (page 1 of 9)