What is electricity? This question brings up a morass of
conflicting
information.
Well, how do scientists use the word? Let's cut through the morass
and ask:
What is the scientific definition for the word "Electricity?"
We'd expect that physicists have a clear definition for "the quantity
of electricity." However, it might suprise you to learn that the
following
sources are unanimous in saying that Electricity is not a form
of energy. Instead, they agree that an electric current is a flow of
"electricity." They also agree that electrons and protons carry charges of
"electricity," and that quantities of electricity are to be measured in
units of charge rather than units of energy. To measure the quantity
of electricity, scientists use the SI unit called the Coulomb.
Quotations from:
- J. C. Maxwell
- J. J. Thompson
- R. A. Millikan
- M. Faraday
- G. J. Stoney
- A. Einstein
- CRC Handbook
- Physics dictionaries and glossaries
1. MAXWELL
During my first research in 1988 about the definition of
"electricity," I found an
excellent quote from James Clerk Maxwell stating specifically that
electricity is not a form of energy. The following is from Maxwell's A
TREATISE ON ELECTRICITY AND MAGNETISM, 1891:
Part I, ELECTROSTATICS, Chapter I DESCRIPTION OF PHENOMENA
Conductors and Insulators
"35] While admitting electricity, as we have now done, to the rank of a
physical quantitity, we must not too hastily assume that it is, or is
not, a substance, or that it is, or is not, a form of energy, or that it
belongs to any known catagory of physical quantities. All that we have
hitherto proved is that it cannot be created or annihilated, so that if
the total quantity of electricity within a closed surface is increased
or diminished, the increase or diminution must have passed in or out
through the closed surface."
<snip>
"There is, however, another reason which warrants us in asserting that
electricity, as a physical quantity synonymous with the total
electrification of a body, is not, like heat, a form of energy. An
electrified system has a certain amount of energy, and this energy can
be calculated by multiplying the quantity of electricity in each of its
parts by another physical quantity, called the Potential of that part,
and taking half the sum of the products. The quantities 'Electricity'
and 'Potential', when multiplied together, product the quantity
'Energy.' It is impossible, therefore, that electricity and energy
should be quantities of the same category, for electricity is only one
of the factors of energy, the other factor being 'Potential.' "
(Also see Part 1, Chapter II, Definition of Electricity as a
Mathematical Quantity, and Definition of the Unit of
Electricity.
-----
Maxwell goes on to point out that *force* cannot be energy, because energy
equals force times distance (if force was energy, then after we
multiplied it by distance, the result could no longer be energy.)
And *mass* cannot be energy because mass multiplied by height gives
potential energy.
So even though Maxwell was writing in 1891, and even though electricity
still contained many mysteries, science had progressed far enough
to figure out that electricity and electrical energy were two different
things.
Also take note that Maxwell defines "Electricity" as a measurable
physical quantity, and not as a class of phenomena.
So what then is "electricity"? Of course Maxwell defines all of his
terminology elsewhere in his book. It's clear from the following
text that Maxwell intends the word "electricity" to mean the same as our
modern phrases "charge of electricity," or "electric charge" ...and that
electric currents are therefore flows of "electricity:"
CHAPTER II Elementary Mathematical Theory of Statical Electricity
Definition of Electricity as a Mathematical Quantity
63.] "We have seen that the properties of charged bodies are such that the
charge of one body may be equal to that of another, or to the sum of the
charges of two bodies, and that when two bodies are equally and
oppositely charged they have no electrical effect on external bodies
when placed together within a closed insulated conducting vessel. We
may express all these results in a concise and consistent manner by
describing an electrified body as "charged" with a certain "quantity of
electricity" which we may denote by "e."
2. THOMPSON
OK, what about J. J. Thompson, the discoverer of the electron? As we see
below, he agrees with Maxwell and defines "electricity" not as energy, but
as charge...
"As the cathode rays carry a charge of negative electricity, are
deflected by an electrostatic force as if they were negatively
electrified, and are acted on by a magnetic force in just the way in
which this force would act on a negatively electrified body moving
along the path of these rays, I can see no escape from the conclusion
that they are charges of negative electricity carried by particles of
matter." - J. Thompson, Phil. Mag, 44, 293 (1897)
3. MILLIKAN
How about Robert Millikan, the physicist who first determined the value
of the electron's charge? He's yet another example of an expert who uses
the word "electricity" to mean electric charge rather than
electrical energy:
"...Faraday found that the passage of a given quantity of electricity
through a solution containing a compound of hydrogen, for example,
would always cause the appearance at the negative terminal of the same
amount of hydrogen gas irrespective of the kind of hydrogen compound
which had been dissolved, and irrespective also of the strength of the
solution; that, further, the quantity of electricity required to cause
the appearance of one gram of hydroben would always deposit from a
solution containing silver, exactly 107.1 grams of silver. This
meant, since the weight of the silver atom is exactly 107.1 times the
weight of the hydrogen atom, that the hydrogen atom and the silver atom
are associated in the solution with exactly the same quantity of
electricity." R. A. Millikan, THE ELECTRON, 1917 p15
Throughout Millikan's book "THE ELECTRON," and also in his autobiography,
Millikan consistently uses the word "Electricity" to mean electric
charge, and saw electric currents as being flows of "Electricity."
4. FARADAY
And what of Michael Faraday himself? In his book "Experimental Researches
in Electricity" from 1839, Faraday investigates the nature of electricity
and frequently uses the term "quantity of electricity" to refer to
quantities of electric charge (rather than to quantities of energy.) As
in Millikan's quote above, Faraday passes a certain "quantity of
electricity" through an electrolysis apparatus to create a distinct amount
of gas or electroplating. Today we call his discovery by the name
"Faraday's Law."
In a section about "
Identity of Electricities," Faraday examines electric eels, examines
the "static" from fur on rubber and from electrostatic generators, as well
as the "current" from batteries and moving coils. Then in the following
passage he concludes that all of these various "kinds of electricity" do
not exist: instead there is only one type of electricity, but one where
the values of current and charge can differ...
"The general conclusion which must, I think, be drawn from this
collection of facts is, that electricity, whatever may be its
source, is identical in its nature. The phenomena in the five kinds
or species quoted, differ, not in their character buy only in degree;
and in that respect vary in proportion to the variable circumstances of
quantity and intensity ['intensity' means current -billb]
which can at pleasure be made to change in almost any one of the kinds
of electricity, as much as it does between one kinds and another."
-Michael Faraday, EXPERIMENTAL RESEARCHES IN ELECTRICITY, vol.1,
1839, p360
See also: "Faraday
as a Discoverer", John Tyndal 1869
5. G. Johnstone Stoney
Here's a quote from G. J. Stoney, who recognized the existence of the
quantum of charge and named it the "Electron" in his paper "Of the 'Electron', or Atom of Electricity", Phil Magazine N5 V38 P418-420 Oct 1894
In this paper an estimate was made of the actual amount of this most
remarkable fundamental unit of electricity, for which I have since
ventured to suggest the name electron. According to this determination
the electron = a twentiethot (that is 10^-20) of the quantity of
electricity which was at that time called the ampere, viz: the quantity
of electricity which passes each second in a current of one ampere,
using this term here in its modern acceptation. This quantity of
electricity is the same as three eleventhets (3 x 10^-11) of the C.G.S.
electrostatic unit of quantity.
6. EINSTEIN
If you're swayed by authorities, then listen to
Albert Einstein, from
his 1938 book Evolution of Physics:
"The electric fluid flowing through the wire is the negative one,
directed, therefore, from lower to higher potential... The next
important question is whether the structure of this negative fluid is
"granular," whether or not it is composed of electric quanta. Again a
number of independent experiments show that there is no doubt as to
the existence of an elementary quantum of negative electricity. The
negative electric fluid is constructed of grains, just as the beach is
composed of grains of sand, or a house built of bricks. This result
was forumlated most clearly by J. J. Thomson, about forty years ago.
The elementary quantity of negative electricity are called electrons."
- Einstein/Infeld, EVOLUTION OF PHYSICS 1938, p 253
So even Einstein believes that "electricity" is not electromagnetic
energy, but instead is the same as Charge (it is Coulombs rather than
Joules.)
7. CRC Handbook of Chemistry and Physics
And how about the ultimate authority in physics? It's the CRC Handbook
of Chemistry and Physics! (Heh. Well, most physicists rely on it as the
ultimate authority.) What does the CRC Handbook say about the quantity
called "electricity?" Is electricity the EM energy measured in Joules,
or is it charges measured in Coulombs?
CRC Handbook, 64th Edition, 1984:
Quantity of electricity or charge -- The electrostatic unit of
charge, the quantity which when concentrated at a point and placed at a
unit distance from an equal and similarly concentrated quantity, is
repelled with unit force...
Coulomb (unit quantity of electricity) -- the quantity of
electricity transported in 1 sec by a current of 1 A. A unit quantity
of electricity. It is the quantity of electricity which must pass
through a circuit to deposit 0.0011180g of silver from a solution of
silver nitrate. An ampere is 1 coulomb/sec. A coulomb is also the
quantity of electricity on the positive plate of a condenser of
one-farad capacity when the electromotive force is 1 v.
The CRC defines "Quantity of
Electricity..." as Coulombs. Also see the National Institute of
Standards and Technology (NIST) website, Table 3
Table 3. SI derived units with special names and symbols
Expression in
terms of
Derived quantity Name Symbol SI base units
electric charge, quantity of electricity coulomb C s * A
8. Various dictionaries of physics
Browsing through various physics glossaries and dictionaries, I find that
most of them have no entry in section "E" for the word "Electricity."
However, knowing that scientists throughout history used terms in very
specific ways, I instead look under section "Q." Bingo! Most
dictionaries have a listing for "Quantity of electricity..." also called
electric charge and measured in Coulombs. A few even have it under
section "C," where they define the word "Coulomb" as the unit quantity of
electricity, or "A," where they define the Ampere as the unit for flow or
transport of electricity. A quick google search finds them:
+"quantity of electricity" +dictionary
But what do today's scientists think of the word "Electricity?"
Going further ahead in history we find that "Quantity of electricity" is
still sometimes used in Europe, while American scientists mostly stop
using the word. They replaced the term "Quantity of electricity" with
"quantity of electric charge," then later shortened this to "quantity of
charge." Scientists of today mostly use the term "electricity" as a
chapter title, or to denote a whole class under which various phenomena
are listed. Anything electrical then becomes a type of "electricity."
So, over the decades "electricity" has stopped flowing in wires entirely!
Instead electricity has turned into something like "physics" or "optics"
or "weather." In the way that wheels and bicycle chains "are" physics,
batteries and wires "are" electricity.
More uses of the "scientific definition" of Electricity:
.