"Radio 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 Radio News magazine 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
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
Part One : An Introduction to the Various Physical Phenomena Underlying Radio
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.
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
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.
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 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
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 Way
Thompson: Elementary Lessons in Electricity
The New Way
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.
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 nuclei. 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
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
This is the Wein cell that produces rather large amounts of electric
energy upon being subjected to an application of light
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.
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.
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 grid.
4. Leakage (drift of electrons through the glass).
5 Positive ions emitted by the filament.
6. 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
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
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 December 31, 2021
(updated from original post on 10/2/2013)