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"ELECTRICITY" AS QUANTITY IN PHYSICS |
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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, when "electricity" flows along, the flow is called an electric current. 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. Also see: Table of differences: Electric Charge versus Electric Energy Quotations from:
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1. MAXWELLIn 1988 during my first research into the "true" definition of the word Electricity, I discovered 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<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 force by distance, the result could no longer be energy.) And in a similar way, *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 first 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 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. THOMPSONOK, 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. MILLIKANHow 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 p15Throughout Millikan's book "THE ELECTRON," and also in his autobiography, Millikan consistently uses the word "Electricity" to mean electric charge, and he saw the electric currents as being flows of "Electricity." 4. FARADAYAnd what of Michael Faraday himself? Does he believe in different kinds of electricity? Nope. 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, or of current.) As in Millikan's quote above, Faraday is passing a certain "quantity of electricity" through an electrolysis apparatus to create a distinct amount of gas, or a fixed amount of electroplating. This is described in his publication "On the absolute Quantity of Electricity associated with the Particles or Atoms of matter." Today we call his discovery by the name "Faraday's Law."In a section about " Identity of Electricities," p360, Faraday examines the sources of the five types of electricity known at the time:
"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 but 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 5. G. Johnstone StoneyHere'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. EINSTEINIf 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."So even Einstein believes that "electricity" is not electromagnetic energy, but instead is the same thing as Charge (electricity is Coulombs rather than Joules.) 7. CRC Handbook of Chemistry and PhysicsAnd 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 the charge measured in Coulombs?
8. NIST Nat. Inst. of Standards, SI physics standards
The CRC defines "Quantity of Electricity..." as Coulombs. Also see the
international metric system: the MKS Standards of the
SI, and the National Institute of Standards and Technology (NIST)
website, Table
3. They define "quantity of electricity" as charge measured in
coulombs, not as energy measured in joules. |
| Table 3. SI derived units with special names and symbols | |||
| Derived quantity
|
Name |
Symbol |
Expression in terms of SI base units |
| electric charge, quantity of electricity | coulomb | C | s * A |
9. Various dictionaries of physicsBrowsing 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:
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 use it in the same way as "biology" or "dynamics:" to denote an entire class under which various phenomena are listed. Anything electrical then becomes a type of "electricity." So, over the decades "electricity" has <grin> stopped flowing in wires entirely! Instead electricity has turned into something like "physics" or "optics" or "weather." In the same way that wheels and bicycle chains are physics, batteries and wires "are" the electricity. Textbooks are full of electricity, but power lines and capacitors are not?
More instances of the scientific definition of Electricity:
Nikola TeslaYou're a denizen of the internet, so the real question on your mind of course is <grin>, what did Nikola Tesla think electricity was? Fortunately it's right in his 'The Problem of Increasing Human Energy.'"Whatever electricity may be, it is a fact that it behaves like an incompressible fluid, and the earth may be looked upon as an immense reservoir of electricity..." -N. Tesla 1900So, Tesla followed Maxwell's insight: wires like water-filled pipes, and the "water" is the vast population of mobile electric charges inside. The ocean of neutral-but-movable charges within wires (and within the Earth,) it behaves like a near-incompressible fluid. Tesla discovered that he could broadcast waves through this fluid (today called Zenneck Surface Waves,) and believed it possible to send out megawatts at lower losses than those present in the power grid. As with the power grid, the waves are the electrical energy, while the Electricity is the medium through which the waves travel. Electricity wiggles back and forth while the waves move continuously forward.
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