Phenomena Underlying Radio
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 1929 that
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
of Contents]These articles are scanned and OCRed from old editions of the Radio & Television News magazine.
Here is a list of the Radio & Television News articles
I have already posted. All copyrights (if any) are hereby
See all available
vintage Radio News
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 them
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
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.
With 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
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.
The Bohr Atom
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
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.
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.
Probably at 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.
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 grid.
4. Leakage (drift of electrons through the glass).
5 Positive ions emitted by the filament.
Electrons emitted from the grid under the influence of light (photoelectric
7. Electrons emitted from the grid under
the influence of the soft X-rays (X-rays of long-wave length) given
off 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 place.
Posted October 2, 2013