August 1932 Radio-Craft
Wax nostalgic about and learn from the history of early electronics.
See articles from Radio-Craft,
published 1929 - 1953. All copyrights are hereby acknowledged.
Whoa, it's a good thing I read these articles prior to publishing
them, lest some uninitiated soul be lead to the wrong conclusion!
Keep in mind that this article was written in 1932, prior to
the development of the quantum mechanical model of the atom,
but on the other hand,
Niels Bohr developed their model in 1913, so the relevant
information was available. The
Rutherford-Bohr model of the atom suggested a nucleus comprised
of positive masses called protons, each of which carries a charge
of +1 unit, and neutrons with no net charge. Surrounding the
nucleus were orbiting masses called electrons, each of which
carries a charge of -1 units. Accordingly, the net charge of
an atom was the sum of protons and electrons, with unionized
atoms having a net charge of 0 (zero).
Neutrons, carrying no charge, have no effect on the overall
Modern science says quarks, three of which make up each proton
and neutron, have individual charges of +1/3, -1/3, +2/3, or
-2/3, thereby determining the particles' net charges
(+1 for protons, 0 for neutrons).
Now, take a look at Figure 3 in this article and the text description
that mutually proves the drawing is not a mistake and the text
is not a typo.
The author correctly believes an atomic nucleus
(in this case an unionized carbon atom,
N=6), which must have a net charge opposite of the number
of electrons (6 for carbon), needs
to be +6 charge units. However, he knows the atomic weight
(mass) of a carbon atom is 12
mass units (each proton and neutron has
approximately 1 mass unit). There cannot possibly be
12 protons or that would yield a net atomic charge of +12 +
(-6) = +6 charge units. He resolves the quandary by proposing
6 additional protons in the nucleus along with 6 additional
electrons in the nucleus. That equal set cancels out the 6 extraneous
charge units, and since the mass of electrons is miniscule compared
to that of protons, their presence does not upset known total
atomic mass too much. I don't ever recall seeing that kind of
model being proposed before.
The irony is that the
raison d'être for the article is to push back the frontier
of ignorance so that the reader might more fully understand
what is happening in an electronic circuit. Otherwise, though,
it is a useful piece.
In a very loose sense, Mr. Palmer's nucleus model is
sort of accurate in that a neutron, when it decays
decay, mediated by the nuclear weak force), produces
proton, an electron, and an electron antineutrino/a>. That
is not the same, however, as saying that a neutron is initially
comprised of a proton, an electron, and an electron antineutrino.
The process is not readily reversible.
I Equals E over R
By C. W. Palmer
The fact that current flow in an electrical circuit depends
upon voltage and resistance means nothing unless one can visualize
what is actually going on. In this extremely novel presentation,
the author shows not only "how" but "why."
A molecule of a substance, say at B Fig.
1, is composed of positive and negative electrons, such as illustrated
at Fig. 2 or Fig. 3. Fig. 4 illustrates the logical sequence
used in breaking down the substance.
People not familiar with electricity have the idea that little
is known about this subject. This assumption is incorrect, as
probably more is known about this science than about any other.
Because mechanical motions and forces can be seen and felt,
it is easy for the average person to understand and foretell
their actions and the results ensuing. For example, few people
would question the result of striking a piece of wood with the
sharp edge of an axe or dropping an egg on a concrete floor;
but when the problem is to visualize what is taking place in
an electrical circuit, they are entirely at "sea."
If we remember that we cannot see or hear electricity directly,
but can only observe its effects, the study of electricity -
and its companion radio - will be much simplified.
Electricity (according to the electron theory) consists of
extremely small moving particles, these particles have been
named electrons and protons. These electrons and protons do
not carry electricity, as some people think, they constitute
electricity. In other words, an electron or proton is nothing
but a small quantity of electricity. Electrons and protons are
separated because they act differently; the electron is said
to be a negative charge while the proton is a positive charge.
The average person usually believes an electron to be a very
small particle of matter; beyond this elementary conception
his ideas are vague and usually confused.
Let us first consider "Matter." Matter is any substance having
weight and volume - the air, the earth, the water, are all forms
The uncharged, separated molecules in Fig.
5 cause a flow of current as shown in the lower part of the
same figure when touched. This flow ceases in a very short time,
but may be caused to flow for a longer time by the application
of an E.M.F. as shown in Fig. 6.
The Atomic Structure
Consider a bar of copper (an element) as shown in Fig. 1.
This bar shows certain peculiarities which identify it as copper,
and even a very small piece, such as B of Fig. 1, cut from this
bar will be characteristic of the whole piece. If it were possible
to keep cutting down the size of the piece of copper, we would
arrive at a point where a further cut would result in changing
its characteristics, and it would no longer be identified as
the same material as the whole. This particle containing all
the peculiarities of the whole piece is called a molecule of
Since the molecule has the same characteristics as the whole,
it, too, must be subdivided if we are to discriminate between
one substance and another. Now, since all substances have different
constituents, their molecules must be different, and science
has been able to break down the molecule into still smaller
particles called atoms. An atom of hydrogen is different from
an atom of helium; an atom of copper is different from an atom
of zinc, etc. Atoms cannot exist by themselves in a normal state
- at least two atoms must be combined to form a molecule.
The atoms of every substance, regardless of its nature, are
composed of electrons. This means that all substances contain
electricity, which seems contradictory to our general knowledge,
although it is apparently true as we shall soon see.
In its normal state, an atom contains a certain number of
electrons and proton arranged in a particular manner. Each substance
has a different combination and grouping of the charges. Hydrogen,
for example, the lightest substance known contains only one
electron revolving around one proton as shown in Fig. 2. Carbon
contains 12 protons grouped together with 6 electrons as a nucleus
around which 6 electrons revolve as shown in Fig. 3.
The central portion of the atom is known as the nucleus and
it may consist of a single proton or a group of protons and
electrons. The electrons revolving around the nucleus are known
as the planetary or free electrons, because they can be removed
from the atom without changing its general character. These
planetary electrons revolving around the nucleus may form a
single ring or a number of rings around the nucleus, depending
on the complexity of the atomic structure of the substance.
The atomic structure is shown graphically in the form illustrated
in Fig. 4 - first, there is the molecule of an element which
is composed of atoms and these in turn are made up of electrons
Single elements, as described, are familiar to all, but many
substances we encounter consist of chemical combinations of
the atoms of two or more different elements forming another
substance - a compound - whose appearance and physical properties
are different from any of the elements, such as salt, water,
For the sake of simplicity, we will limit our explanation
to the elements and atoms.
We have shown that atoms are composed of minute charges of
electricity which, normally, are in such a form that the sum
of the charges of all the electrons or negative charges equal
the sum of the charges of all of the protons or positive charges.
We have also explained that some of the electrons are revolving
around the nucleus in orbits in a manner similar to the stars
around the sun. It is to be noted that although the substance
contains electricity, (electrons and protons) it is uncharged
simply because the charges are equal and balanced.
If we remove one or more of the planetary electrons from
an atom, the atom becomes unbalanced and lacks negative electricity
(electrons). In this case, the atom is said to be positively
charged. On the other hand, if we place an additional electron
or electrons in one of the planetary orbits of an atom, it also
becomes unbalanced - in the opposite direction - and has too
much negative electricity (too many electrons). In the latter
case, the atom is charged negatively.
From this it can be concluded that a substance is electrified
when it has more or less than its normal number of electrons
and the amount of charge is determined only by the quantity
of electrons displaced. Also, it can be deducted that all electrons
are the same regardless of the element or compound from which
The Electric Current
Every substance has a tendency when displaced from equilibrium,
to return to a state of balance as quickly as possible. Just
as water will find its own level, so atoms which have lost electrons
(positively charged) will attempt to attach electrons to themselves,
and atoms which have excess electrons will attempt to loose
them and thus become neutral.
Therefore. if we have two substances, one charged positively
and the other charged negatively, and we touch them together;
the excess electrons from the negative will enter the other
substance in order to reach a neutral state. If the two bodies
are charged equally (and oppositely) the electrons will continue
to transfer until both substances are neutral.
Figure 5 shows this effect. In the upper part of the illustration
the two substances are charged; and in the lower part, the excess
electrons from the negative body have entered the positively
charged body and neutralized the atoms lacking electrons.
If we have some means of maintaining the charges on the two
balls (shown in Fig. 5.,) continuously, there would be a constant
passage of electrons from the negative to the positive ball.
This continual passage of electrons is what is known as an electrical
current or simply a current. This follows logically from the
statement we made before; that electrons are electricity.
It is not possible to add or remove electrons from a substance
without the aid of some external force. This force is known
as an electromotive force (E.M.F.). We will not go into the
various means of maintaining an E.M.F., here. Several common
sources of electromotive forces are dry batteries, storage batteries
The amount of current flowing in a circuit (for example the
two balls in Fig. 6) depends on the number of electrons passing
through the circuit. The number of electrons, in turn, depends
(among other things) on the amount of the charge which is dependent
on tile E.M.F. applied to the circuit. We may safely conclude,
therefore, that the amount of current flowing in a circuit depends
on the value of the E.M.F. applied to the circuit.
When visualizing the motion of electrons through a solid
body, such as copper, we must remember that the electrons are
very small and that there are comparatively large spaces between
the atoms. As an example, if a copper cent were enlarged to
be the size of the earth's diameter, the distance between atoms
would be about three miles and the electrons would be only a
few inches in diameter!
It is well known that certain materials such as copper, brass,
silver, etc. will readily permit the passage of an electric
current, while other materials such as rubber, mica, porcelain,
cotton, silk etc., do not. The former materials are called conductors
and the latter, insulators. The reason why metals are such good
conductors of electricity is that their atoms apparently have
a weak attraction for electrons and large numbers of them are
either practically in a free state throughout the body of the
metal or they are easily shifted by any outside electric forces.
The more easily the electrons can be shifted in a metal, the
lower its resistance to a flow of current, merely because a
greater current flows for the same value of applied E.M.F.
This action of resistance in conductors introduces another
factor in the consideration of the strength of current flow.
Up to this point we have seen that the amount of current increases
as the E.M.F. increases and since the opposition offered by
the conductor of the current decreases the current, it may be
said that the magnitude of the current flowing in any circuit
depends upon the E.M.F. applied and the opposition offered by
the circuit itself.
In order to facilitate the measurement and computation of
electric currents, several units have been set as standards.
The E.M.F. is measured in a unit called a volt; the current
is measured in amperes and the opposition or resistance is measured
in ohms. The first of these units is usually represented by
the letter E, the second by the letter I and the resistance
by the letter R.
To sum up: the current (number of amperes) flowing in a circuit
depends upon the voltage applied and the resistance of the circuit.
To state this in another way,
A problem involving this condition is shown in Fig. 7. This
involves a resistance of 5 ohms in a 10-volt circuit. Then
or 2 amperes.
Another type of problem might arise in which it is desired
to know the value of the resistance in a circuit when the voltage
and the current are known. Here again, Fig. 8 illustrates the
conditions. This may be determined from the ratio
or if the potential (volts) is 50 and the current is 2 amperes,
the resistance will be 50/2 or 25 ohms.
The third condition of the relation considered above is one
in which the resistance and the current are known and it is
desired to know the applied potential. In this case. the voltage
E is equal to the product of the current and the resistance
(E = I x R).
If a current of 10 amperes is flowing through a resistance
of 20 ohms, then the potential applied is 10 x 20 or 200 volts.
From these three examples. it is established that there are
three individual conditions involving the relation of E.M.F.,
current and resistance. These three classifications are as follows:
When E and R are known and the current is desired:
E = I/R
When E and I are known and the resistance is desired:
R = E/I
When R and I are known and the voltage is desired:
E = R x I
The above three formulas are known as Ohm's Law in honor
of the noted physicist George Simon Ohm.
Resistances in Series
We have already learned that resistance is the opposition
of a substance to the flow of current. It is natural then, that
the longer the substance composing the resistance, the greater
will be the value of the resistance. Also, if two conductors
are connected so that the current passes through each of them
in succession, then the resistance of the circuit will be the
sum of the individual resistances of the two conductors. This
effect is illustrated at Fig. 8. The resistance of the conductor
at 8A is R. Then the total resistance of the two resistors at
8B is the sum of the individual resistances.
When the area of a conductor is increased, the opposition
to the flow of current will be decreased, as there are more
atoms to lose and gain electrons. It also follows logically
that if two conductors are connected as shown in Fig. 9, the
resistance of the circuit will be less than that of either of
the individual resistors R. This is known as a parallel method
The method of figuring the total resistance of the circuit
for parallel resistances is different from that for series resistances.
If we refer again to Fig, 9, it will be noted that the current
flowing from point A to point B will be divided and part of
it will pass through each resistance. If these resistances are
equal, half the current will go through each, Then, if the applied
E.M.F. is 10 volts and the current in each resistor is 1 ampere,
the resistance of each of the resistors will be 10/1 or 10 ohms.
However, the total current flowing is 2 amperes, so the resistance
of the parallel circuit is 10/2 or 5 ohms.
For those readers who are familiar with the elements of algebra,
the above reasoning may be expressed in the following formula:
in which R is the total resistance and resistors R1, R2,
etc., are the individual resistances of the parallel circuit.
The discussion of electricity and resistance given should
be of assistance to many radio enthusiasts who are confused
by the explanations of Ohm's Law usually given. It is suggested
that the article be read over several times so that the details
discussed will all be understood.
(It might be well to add that the
current through a given part of a circuit will vary directly
as the applied E.lM.F. and inversely as the resistance, as stated
by Mr. Palmer. It should be emphasized, however. that when part
of a circuit is under consideration, the current, voltage and
resistance of that particular part should only be considered,
regardless of whatever else occurs in another part of the circuit.
Posted July 9, 2015