Phenomena Underlying Radio
April 1932 Radio News Article
apparatus of today, including television, uses practically all of
the physical phenomena capable of being controlled by science."
That is the opening line of a 1932 article discussing the relatively
new technology dealing with the generation AND controlling
of electrical charges. Investigators were beginning to develop formulas
and physical rules for the behavior of electrons - at least in accordance
with the accepted Rutherford-Bohr atomic model. It wasn't until
Robert Van de Graaff invented his eponymous generator, before
which scientists like Volta used an
electrophorus (Latin for "electricity bearer") to generate static
electrical charges for experimentation by beating a metal disc with
an animal skin to transfer electrons. By 1932, Heisenberg's quantum
mechanical theory of matter was coming into dominance, and not too
much later it would be necessary to apply laws of relativity to
explain the reason why fast-moving streams of electrons (beta rays)
inside recently developed cathode ray tubes did not deflect as much
as predicted based on classical Newtonian models of force and acceleration.
April 1932 Radio News
Wax nostalgic about and learn from the history of early electronics.
See articles from Radio &
Television News, published 1919 - 1959. All copyrights hereby acknowledged.
Phenomena Underlying Radio
An Introduction to the Various Physical Phenomena Underlying Radio
By E. B. Kirk
Radio apparatus of today, including television, uses practically
all of the physical phenomena capable of being controlled by science.
Devices which can be assembled within the space of a few cubic feet
involve actions and energy transformations ranging over the whole
domain of physics. Sound, heat, light, electro-static and electro-magnetic
changes, as well as the dynamics of moving parts, are linked together
in a chain of interactions which require study if we are to understand
Triple Neon Tube
This complicated lamp
which is used for television combines the phenomena of ionization
and production of light and necessitates an understanding
of the Kinetic theory of gases and the science of electronics.
In the days of "wireless" and crystal detectors we
did not have much technical ground to cover. Current electricity,
magnetism, electrostatics and electromagnetics sufficed for us to
have a fairly intelligent insight into the working of our apparatus.
But the vacuum tube and its rapid development opened a new realm
and its apparently unlimited versatility has kept us studying ever
since. Then the vogue of broadcasting, bringing in the microphone
and the loudspeaker, confronted us with the study of sound. Further,
the circuits required for the handling of frequencies became much
more intricate than those used with our early headphones and code
signals. Now, with television stepping on the stage, even more is
demanded of us. Electronic effects, known only in the laboratory
a few years ago, are in common use. We have to understand optics,
piezo-electric devices, light valves, cathode-ray scanning - and
this list is increasing daily.
This means that we have to
review our physics, brush up on optics, and even if our time does
not allow us to read the many technical reports on electronic research,
we can, from time to time, study a resume of the more important
items. With this in mind, the present series of articles was planned.
Present Theory Review
For a better
correlation of the various fields of physical action, and in order
to reduce our explanations to the simplest terms, we can begin with
a review of the present theories of matter and energy.
this as a background we can proceed to the electronic and photo-electric
effects, such as the Barkhausen tube and the production of the so-called
quasi-optical waves and other effects of interest at the moment.
Optics need more than passing attention; the neon tube as a source
of light for television and the polarization of light and the means,
such as mechanical, electric and magnetic devices, for controlling
its action. Next there are a number of magnetic effects which are
interesting. Some are being used. for example, magnetostrictive
action; others are being worked with and give promise of becoming
important. Finally there are certain miscellaneous electrical and
chemical phenomena to be touched upon.
The three units with
which the physicist attempts to explain all the phenomena of the
universe are: the electron. the proton and the photon. The first
two of these involve matter and electrical charge, which, of course,
is a form of energy; the third deals with energy alone. The electron
is the smallest particle of negatively charged matter, and the proton
is the smallest particle of positively charged matter. The photon
is a unit of radiant energy and is the smallest amount of energy
of any particular frequency.
In the above definition of
electron and proton we see that matter and electrical charges are
tied together and both are reduced to a concept of individual particles.
There seems to be no way of getting away from this double definition
- of disentangling the two, matter and electricity - for an electrical
charge has never been absolutely separated and observed as such,
and matter in any of its forms has never been shaken of its ever-attendant
electrical properties. If we open an elementary textbook on physics
we find that matter is defined as anything which occupies space
and which possesses certain properties known to us through our senses.
We know from our experience that electricity is a form of energy,
that energy is commonly defined as the ability to do work. Modern
theory, however, has more to say on these points. The solid atoms
of half a century ago which were considered as occupying space,
in a literal sense of the word, are now thought of as merely centers
of attraction or repulsion. electrical in nature, and an even more
radical conception pictures the electron as a group of waves. Light,
radiant heat, and radio waves. all of which are forms of energy,
have been shown to differ only in their frequency of vibration.
Thus slowly the idea that matter and energy are the same, or that
they are both expressions of a more fundamental cosmic property,
has gained ground; that matter may be transformed into energy and
pass off in radiation similar to radio waves, under certain circumstances,
and conversely that energy may be converted into matter at some
distant point of the universe is accepted by such authorities as
Millikan and Jeans.
We shall have to assume that the reader
is familiar, in a general way at least, with the Rutherford-Bohr
atom model and that he understands the arrangement of the electrons
and protons in the atoms and how the atoms of one element differ
from those of another. Let us recall to mind certain details. In
the normal state the positive and the negative charges, within the
atom, balance each other, leaving the atom electrically neutral.
Disturbing forces may result from a change caused by the distribution
of the charges in the atom; mechanical impact of atom with atom,
or atom with electron; or radiant energy, as a stream of photons,
for example, light or X-rays which disturb the inner atomic forces.
Some of the planetary electrons are less tightly held in their orbits
than others, and therefore a disturbing force may be able to "knock"
them entirely out of the atom or to cause them to move to other
orbits for a period of time. An atom may also temporarily attract
an additional electron. But whenever the normal state is disturbed
and there is either an excess or a deficiency of electrons, the
condition is unstable and as soon as the disturbing force is removed
the atom will tend to assume its normal neutral state with all of
its electrical forces balanced. Lastly, since the electron has only
1/1800 of the mass of a proton, practically all of the mass of an
atom may be considered as residing in its nucleus, which explains
why electrons move at much greater velocity than atoms or ions.
The old and new ways of producing electricity
are illustrated above. At the left is the electrophorus. A resinous
cake is beaten with cat skin and negatively electrified. A metal
disk is placed upon it so that it is charged negatively above and
positively below. When touched with the finger the negative charge
is neutralized and the metal cover may be lifted by the handle and
will be found to be charged with high positive potential. In the
newer method, as shown at the right, Dr. Van de Graaf is able to
produce over a million volts between two large metal balls by revolving
bands of silk with a motor so that frictional charges are built
up on each of the balls .
|The Old Way
Thompson: Elementary Lessons in Electricity
|and The New
So much for the individual atoms. The attractive and repulsive
forces which hold the electrons and the protons together, within
the atoms, are also used to explain the association of one or more
atoms in definite arrangements in the formation of molecules. In
such a process electrons may be radically redistributed. The orbits
of the electrons of each atom may become interlaced and in certain
cases an electron may revolve around two nucleii. In any event,
the combination of atoms to form molecules is very complicated and
we need not consider the details of the process but only remember
that matter in any form, gaseous, liquid or solid, is built up out
of atoms and atom groups. In crystals the spacing is very regular,
but not necessarily the same in the three dimensions, and in complex
molecules (organic compounds) composed of a thousand or so atoms
the relation of one atom to another remains the same within certain
limits, else the compound breaks down into simpler arrangements.
Open Space Between Atoms
This is the Wein
cell that produces rather large amounts of electric energy
upon being subjected to an application of light
In all material,
however, there is "open space" between the atoms and molecules which
is vast, relative to the sizes of the atoms and electrons. This
openness of the structure of solid material is difficult for us
to appreciate, for if atomic distances are given in the usual units
used to measure them, they mean little to us. A comparison, however,
will make these space relations within matter more easily appreciated.
Millikan, in his book on the electron, says of its size: ... "Its
radius cannot be larger in comparison with the radius of the atom
than is the radius of the earth in comparison with the radius of
her orbit about the sun," ... "The electronic or other constituents
of atoms can occupy but an exceedingly small fraction of the space
enclosed within the atomic system."
This explains why it
is possible for high-speed electrons and even helium atoms to be
shot through the glass wall of a highly evacuated tube without,
in the slightest, affecting the vacuum of the tube, for these particles
can pass as readily through solid matter as a comet can pass among
the planets of our solar system. It also explains why sodium of
potassium can be passed, by electrolysis, through the solid glass
of an ordinary electric-light bulb for the preparation of a photoelectric
Let us take for example a metal conductor, a piece
of copper wire. The atoms are spaced with the same relative openness
as we have just considered. The electrons of the atoms revolve around
the nucleii, and the atoms themselves are moving and turning in
every imaginable manner, due to thermal agitation, and in their
state of continually rushing about they are colliding with one another.
In a collision of one atom with another an interchange of energy
may take place, one atom may lose momentum, the other gain it. There
may be an interchange of electrons, electrons may be knocked free
of the atoms or caused to change their orbits, or energy may enter
the body in the form of photons. The possibilities are innumerable.
What is the importance of considering these general cases,
we may ask. The importance is that if we have a reasonably clear
picture of what theory says is taking place, we will be able to
apply simple reasoning to the various phenomena, such as piezo-crystal
action used for constant-frequency oscillators; magneto-strictive
effects used in loudspeakers, in oscillators, and in measuring instruments;
photoelectric phenomena. so important in television and in talking
pictures; why a vacuum tube without a heated filament is possible;
why photoelectric cells are more sensitive to light of one color
than to another; how polarized light can be controlled by electric
fields and other phenomena being used in both radio and television.
Returning now to our piece of wire - a great number of atomic
and electronic interchanges of energy are taking place resulting
in the liberation of free electrons. These electrons, in the case
of copper, do not get very far before they attach themselves to
other atoms with never a relatively great number of electrons free
at any instant, due to the magnitude of the forces within and between
the atoms of copper. When a potential is applied to the wire the
electrons will tend to drift in one direction, constituting the
current through the wire. There are, as we will see later, some
elements in which the production of free electrons at ordinary temperatures
is sufficient to be useful. Now suppose we heat one end and make
provision to keep the other end cool. The agitation of the atoms
will be increased in the heated portion, thus increasing the number
of free electrons, which means a difference of potential between
the two ends of the wire, the hot end becoming negatively charged
(for iron, this effect is reversed). Here we have the heat, the
kinetic energy of rapidly moving atoms, being transformed into an
electric potential. This is known as the Thomson effect.
There are many other interactions of heat and electricity which
we will consider in more detail later, some of which are worth studying
with an eye to useful application, for there is always the possibility
of applying a well-known effect in a novel way. We have a beautiful
example of just such in the apparatus very recently developed by
Dr. Van de Graaff at the Massachusetts Institute of Technology for
the production of a potential of 1,500,000 volts, in which he made
use of the friction of an insulating material against two rapidly
moving belts of silk, each belt charging a large metal sphere, between
which the potential was developed. The production of electricity
by friction has been known for centuries, but never has been so
cleverly applied. Many have attempted to produce these high voltages,
but no one has used such a simple apparatus. The Van de Graaff apparatus
costs about $90, while more complicated machines, such as generators
and transformers, cost many thousands and are much less reliable
in action. We may add that Dr. Van de Graaff is building a much
larger apparatus with which he expects to develop as high as 15,000,000
volts. There is serious talk of considering a modification of the
apparatus for the commercial production of small current, since
as an electrical machine it is very efficient. At the moment this
may seem remote in interest from radio, but it is not impossible
that such a machine might be used to good advantage for supplying
small, steady currents for tubes.
Again returning to the
copper wire: any mechanical disturbance of the piece of copper will
effect the motion of the atoms and the distribution of the forces
within and between the atom, thereby affecting the balance of free
electrons and the rate at which collision and interchange take place.
Compression, tension, twisting, bending, any external force has
to be met by a rearrangement of internal forces and such a rearrangement
changes all the so-called properties of the copper electrical, magnetic,
thermal, optical (in the strict sense of the word the piece of copper
isn't the same). In fact, we are justified in making a generality:
if any change is made in one of the physical or chemical properties
of a substance, inevitably changes occur in all the others. On first
consideration such a sweeping statement may seem entirely unwarranted,
for the question may be asked. "Do you mean to say that if light
falls on a piece of copper its electrical actions are changed, or
the reverse? Does this mean that sound waves impinging on the copper
would change its resistances or that a magnetic field would result
in optical changes?"
Yes, it means just that, but we must
hasten to add that some of these changes may be beyond our present
instruments to detect, or rather that, with some substances, some
of the changes may be so minute as to be immeasurable at the present
time. Copper exposed to light does not produce great numbers of
free electrons which have the velocity to escape from the attraction
of the copper wire, but potassium, another element, does give off
measurable quantities of these photoelectric electrons and cesium,
still another element, reacts even better and is, for this reason,
used in some photoelectric tubes in preference to other substances.
In this case it is a question of the quantity, not the quality,
of the action; likewise with iron and magnetic changes. The forces
within iron allow the greatest changes to be evident, but magnetic
action takes place in all other substances.
this point we had better answer a question which has no doubt come
to mind. What is meant when it is said that all the variables but
one are held constant in an experiment or a measurement, as in the
case of holding the plate voltage and filament current of a tube
constant while the grid voltage is varied in order to see how the
plate current varies? Or is this possible? Theoretically it is not
possible, but so far as the accuracy of our measurement is concerned
the very minute variation in the other factors caused by the change
in the grid voltage is insignificant. And so with any set of forces,
one or two of the group may be going through very rapid changes
of magnitude, but the others are but slowly and minutely varying.
This is not as theoretical or outside the realm of practice as we
may imagine, particularly in the field of vacuum tubes and the electronic
arts, where we are dealing with only a relatively few electrons
at a time.
For example: Recently a vacuum tube has been
developed by B. J. Thompson, of the General Electric Company, which
is capable of measuring 0.000,000,000,000,000,01 amperes. This means
that as few as sixty-three electrons per second can be detected.
With such detection as this made possible, we may expect to see
more of the interactions of matter and energy put to work.
It is interesting to read that Thompson in designing this tube
was forced to consider the following phenomena as sources of current
within the tube:
1. Electrons from the filament.
2. Positive ions (which are atoms with a deficiency
of electrons formed by collision between the electrons
constituting the plate current and the gas molecules in the space).
3. Electrons emitted due to the temperature of the
4. Leakage (drift of electrons through the
5 Positive ions emitted by the filament.
6. Electrons emitted from the grid under the influence
of light (photoelectric electrons).
emitted from the grid under the influence of the soft X-rays (X-rays
of long-wave length) given
by the plate due to its bombardment by the plate current.
In the above list we see the importance of atomic, electronic
and photon (light and X-ray) interaction, and how, when our attention
is directed to greater and greater accuracy, we must take account
of more and more factors.
It is very natural for us to be
so familiar with a phenomena, having in our mind the most astounding
actions involved, that we do not stop to think of the multitude
of lesser effects. We have seen this in the above example, for one
does not usually think of a vacuum as a producer of X-rays. Another
example, under our nose, is the modern pentode tube. Years ago,
if a vacuum tube "blued" it meant that there was gas present which
was being ionized sufficiently to be luminous (similar to a modern
neon tube). When a good pentode "blues" it is not due to the ionization
of gas but to the fluorescing of the glass due to bombardment by
electrons which have missed the plate.
We have covered a
lot of ground in attempting to point out that electrons, protons
and photons are the mechanisms with which the physicist has been
able to explain the various forms of energy and their interactions.
Our review may seem to lack precision because we have not expressed
the relations between the various factors in mathematical form,
introduced equations and formulas. As we proceed, in following articles,
to consider in more detail the phenomena which we have been enumerated
above, we will be able to get down to definite quantitative relationships
in some cases, but even then it is hoped, by a non-mathematical
approach, we will be able to form our picture of what is taking