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B What is Electricity? Insights please...

  1. Mar 18, 2017 #1
    I have some couple of questions about this topic to keep this as concise.
    1)First of all why does electricity flow in the opposite direction to electron flow?
    2)What is electricity in relation with a electron? I know it is the proportional to electric charge, but what relation does it hold? Is it like Inertia to mass? Something from that perspective.
    Thank you for reading my question.
     
  2. jcsd
  3. Mar 18, 2017 #2

    davenn

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    It doesn't ... it IS the flow/movement of electrons ( the positive to negative thing came about before electrons were known about )

    electricity is the flow of charge, the electron is the charge carrier
     
  4. Mar 19, 2017 #3
    Which way it flows is up to you. You can visualize the direction of current as the same as electron motion, or (more commonly) the opposite of electron motion. It makes no difference as long as you're consisent.
    Electricity arises from a force field that electrons and protons possess. Electricity is a surplus/deficit of charged particles. The quantity of electricity is measured in coulombs.
     
  5. Mar 19, 2017 #4

    sophiecentaur

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    You are using the word "electricity" inappropriately here. "Electricity" is a catch-all word which refers to the whole phenomenon. It is not a quantity. What flows is Electric Charge. The rate of flow of electric charge past a point (Coulombs per second) is the Electrical Current.
    As dave has said, the direction of flow of Electric Charge is the direction of the Current. It just happens that the (recently discovered) electron is what carries the charge in metal wires. A negative charge flowing one way is the same as a positive charge flowing the other. There needs to be no confusion and certainly no-one "got it wrong" as students love to say. Forget about electrons in everyday electronics discussions. That avoids any confusion and, in any case, the same rules apply however charge may be flowing through a component. Annoyingly enough for students, the electron is pretty well irrelevant for basic electrical problems. For some reason, 'Educators' decided that even young kids should know about electrons and so the rot set in. . . . everyone wants to bring the little devils into every discussion.
     
  6. Mar 19, 2017 #5
    Just to point this out more explicitly, the reason why *positive* current flow direction actually corresponds (most often) to negative electrons moving the opposite direction, is really just a historical artifact. Upon Discovery of electricity, people realized there are two opposing "signs" of electricity, but which would be called positive and which negative, was up to pure definition. It was a 50/50 chance of getting it correct, they chose wrong in the end.
    Mind you, when it's actually positive ions flowing instead of negative electrons, as in for example a battery, then the direction of current flow is the same as the direction of charge flow.
     
  7. Mar 19, 2017 #6

    anorlunda

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    That's correct, but I want to point out that "they" was our beloved Benjamin Franklin.
     
  8. Mar 19, 2017 #7

    sophiecentaur

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    Wrong! They chose what happened to be the more 'confusing' of the two options for people who do not want to treat Electricity as the abstract phenomenon that it is and who insist on a mechanical view.
     
  9. Mar 19, 2017 #8
    "They chose" what was necessary to record phenomena and make progress in science. A test charge was taken to be a +ve charge and all rules about current, electrostatic effects, magnetic effects of "current" are based on the +ve test charge.
    I challenge you to find a respectable text book that denies the role of "electrons" as useful in the explanation of many electrical phenomena.
    In a similar way one end of a bar magnet is chosen to be called "North"
     
  10. Mar 19, 2017 #9

    sophiecentaur

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    What level are you referring to and what phenomena? Electrons are presented to 11 year olds, age a time that the basics of simple circuits (not with numerical examples). All that can achieve is to present them with cognitive dissonance. Electrons are not a Concrete concept yet Elementary Science tells kids that they are. A text book (and I could show you many Key Stage 3 books and National Curriculum publications) that insist on making the connection. Even my A level course of many decades ago did not require particle flow for working out circuit problems. It was, of course, acknowledged that electrons are involved but the point was, they were not included in any 'reasoning' about how the classical phenomena are all described and how calculations can be carried out. Until the way electrons actually behave in the free state is appreciated, there is only confusion available to the beginner at Electricity. When I learned my Science it was admitted that certain aspects (most, actually) are hard and were not approachable by simple arm waving. Nowadays, everything has to be approachable. Consequently, many students resent the idea that there is learning and discipline involved.
    The way that electric current flows depends entirely on the context. I agree that electrons are the carriers of charge in metals but that is not 'fundamental'; it's a particular instance. That is why I take issue with the word "wrong".
     
  11. Mar 20, 2017 #10
    The assumption was that something traveled through the wire, but they had no way to establish what the direction was. So they defined, arbitrarily, one start to be the Plus end, the other the Minus end, and said that this substance was traveling from Plus to Minus. It simply so happened that for the vast majority of cases they looked at that "substance" was actually electrons, and the direction of flow was exactly opposite of what they thought.

    @sophiecentaur , I don't know what the purpose of your endless tirades is on this forum about how to "properly" learn. People ask questions here, and there is no cookie cutter approach to how to enlighten somebody. In fact, your "my way or the highway" approach likely alienates a lot of people who otherwise would understand the matter in a slightly circuitous way. I don't know whether you've ever been a teacher, but any teacher with experience will tell you that the art of teaching is to first understand the student's misconceptions, not by forcefully cramming the "right way" down somebody's throat. And a pro tip, open your reply with "Wrong!" will make everybody ignore you very quickly.
     
    Last edited: Mar 20, 2017
  12. Mar 21, 2017 #11

    sophiecentaur

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    I am sorry but I feel strongly about this. I have a lot of experience of students of many ages and I have see the results of insisting that intuition and bad analogies are the way to a 'valid' Science education. I had many students who were not prepared to 'learn' stuff (what I told them or what was in their text books). They never managed to crack it. The ones who did well in their exams and who showed good understanding were all able to quote the relevant (boring?) facts, Maths and Formula back to me. Going down an 'alternative' route to Science is only fruitful when you already know the established route well. All those tiresome details are the toolbox to allow progress.
    I had 20 years of A level Physics teaching. I spent many hours discussing misconceptions and getting into the heads of students so I could see where they were coming from. That's a very satisfying and exciting process (both ways) and I nearly always felt justified on stressing that, at Student Level, the accepted way would allow them to progress. Funnily enough, it was the ones who didn't actually want to get down to serious graft and tried to insist that their alternative approach was the way to go, who fell by the wayside.
    People always quote the great minds who did their own thing and who came up with magic breakthroughs by inspired lateral thought, as if that proves you don't need the conventional way through. Fact is that every one of them started with a very thorough grounding in the basic, accepted stuff. 'Proper' learning involves the discipline of basic ground work and not taking the apparently easy way of following intuition. The Science Establishment is notoriously conservative and perhaps over protective but that is a necessary condition to avoid wild swings that take us nowhere. Critical damping rules.
     
  13. Mar 21, 2017 #12
    Questions of manners aside, I have to side with @sophiecentaur here. We could get some more EE's in the room and I think they would agree relative to the subject matter. In particular I agree very much with comment #7 that too often, simplistic notions of electromagnetism are taught in our schools (certainly in U.S. schools) in which mechanical metaphors are used in place of the more scientific but also more abstruse conceptions offered by physics. Since this is a physics web site, it would seem appropriate not to offer up the mechanical metaphors in response to the OP's question.

    I should clarify that I'm not an EE myself; however the reading I've done over the past 3 years has made it pretty clear how easy it is for even good students to learn mistaken concepts when taught outside of a physics framework or outside of the relatively few good presentations of electronics as a craft.

    There is an excellent book available, written by a UK-based EE, Merlin Blencowe, about valve-based audio amplification circuits for electric guitars; the first chapter is something of a primer about various concepts in electronics; and at a certain point early on, he includes a lengthy footnote about misconceptions to do with "current" in particular. It's just a footnote, but it's worth reading, as he lays out clearly the distinction between why it's useful at times to speak of current "flowing" vs. the fact that this is only a metaphor, and doesn't quite jibe with actual math-based physics models. The book is Designing Tube Preamps for Guitar and Bass, and here's a link to the first chapter as a PDF; the footnote can be found on p. 3.

    Here's the text in the main body of the chapter that leads to the footnote, which is marked with an asterisk:

    New electrons continue to boil off the cathode to keep the space charge topped up, so altogether we have a net transferral of negative charge from cathode to anode. If we reckon current as flowing from cathode to anode then it must also be negative, but since most people prefer to work with positive numbers it is easier to say that a positive current flows from anode to cathode, as this amounts to exactly the same thing.*​

    And here's the first few paragraphs of the footnote, just to whet the appetite for reading the whole thing:

    * This sometimes causes consternation among students who argue that conventional current ‘goes in the wrong direction’, but this arises due to a misunderstanding of what current actually is. The confusion is understandable because we often describe current as being a flow of electrons, and immediately form a convenient mental picture of what is happening inside conductors. But while this explanation is good enough for everyday conversation, it is not the whole truth.​

    Strictly speaking, current does not have any direction in the usual sense because it is not a physical ‘stuff’ that moves around a circuit. Current is more properly defined as the rate of change of electric flux: ##i = dQ/dt##, and is, therefore, an entirely mathematical concept. Current is a scalar quantity; it has no direction, only sign (positive or negative).​

    The misunderstanding is further compounded by the limitations of the English language which was never designed to cope with the peculiarities of quantum physics. The word current actually means the same thing as flow, and does not imply a particular direction, yet it is standard practice to describe circuits using phrases like “current flows from A to B”, when technically this is nonsense.​

    Also helpful (if a bit ranty at points) is a series of articles by William J. Beaty, an engineer, in which he tries to point out typical misconceptions about how EM is taught, versus more accurate representations arising out of physics; here's a page with an index to the articles: MISCONCEPTIONS SPREAD BY K-6 TEXTBOOKS: 'ELECTRICITY'
     
    Last edited: Mar 21, 2017
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