Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Help me understand electricity.

  1. Jul 29, 2012 #1
    I don't care to understand how to measure it, just want to understand how it works. First help me understand how a basic rechargeable fluid battery system works.

    Please understand i have an 8th grade education, a ged, and some tech school. I had to teach myself alot.

    How i understand it after reading alot. Within the battery is posotive and negative ions. When a copper wire is introduced, touching - and + ends, -ions flow to the +end of battery, pass their -charge through the wire. (becomming atoms?)

    Positive ions flow toward the -End of battery, picking up the -charge from the -end of battery.(becoming atoms?)

    I'm sure i'm wrong, because i think i remember reading that molecules disolved in a solution kinda break apart and become negative and positive ions(depending on the molecules and possibly solvent) So also...can atoms exist in a liquid solution in which they are soluble?

    I did thing the electrons flowed through the wire, but then read on here that it dosent really flow, it passes chage, as in the electron is jacked up into a higher orbit, or has more energy, and passes the higher energy alog.

    So if i alter my understanding with that i come up with....

    Charging the battery would be passing the high energy state to the electrons in the -ions in the battery.

    Using the energy would be using the extra energy given to the electrons(from charging) within the -ions, while the posotive ions never loose energy.

    Is that close?
  2. jcsd
  3. Jul 29, 2012 #2
    The chemical reactions depend on the type of battery. The Daniell cell has the easiest reaction

    There are no molecules breaking apart in a Daniell cell. There is copper sulfate and zinc sulfate. Both are salts, that means these substances consist of ions. Ions are either atoms or molecules that are electrically charged. Copper sulfate for example consists of positiv copper atoms and negative sulfate molecules. When it is dissolved in water the ions can move around freely.
    At the zinc electrode zinc atoms are loosing electrons and become positive zinc ions that dissolve in the water. The electrons then flow through the wire and into the copper electrode and combine with a positiv copper ion that then becomes a neutral copper atom and deposits on the copper electrode. Neutral copper or zinc atoms can not dissolve in water, they need to be charged first to do that. The negative sulfate ions are not doing anything.
  4. Jul 29, 2012 #3


    User Avatar
    Science Advisor

    I did thing the electrons flowed through the wire, but then read on here that it dosent really flow, it passes chage, as in the electron is jacked up into a higher orbit, or has more energy, and passes the higher energy alog.

    Don't believe everything you read here.

    Electric current still consists of electrons. It is just that the electrons that enter a wire are not the same ones that come out of it.

    This is because there are billions of electrons already in the wire.

    If you like, the electrons at the far end of the wire get shoved out by new electrons coming into the wire.

    From a practical point of view, it doesn't matter what really happens in the wire, or in the battery.

    Wire conducts electrical current.
    If it is copper, it conducts it better than if it was iron.
    It conducts better (ie has less resistance) if it is thick than if it was thin.
    It has less resistance if it is short than if it was long.

    We just regard a battery as a source of power.
    It has a voltage and it has internal resistance which limits how much current it can produce.
    The Chemists can worry about how to make them.

    If you really want to get involved with electricity, (using safe low voltages) the best thing to do is to get a $15 digital multimeter and start measuring things..
    Which materials have high resistance and which have low?
    Can you tell which flashlight batteries are flat and which are new, just by measuring their voltage? How about the battery in your watch?
  5. Jul 29, 2012 #4

    jim hardy

    User Avatar
    Science Advisor
    Gold Member

    that's a fact you want to latch on to for your mental models.
    Like water in a pipe, the water moves slowly
    but a pressure change is transmitted at about speed of sound in the medium.

    it sometimes causes people to go off on a wrong track if they think the electrons in a wire move fast.
    The fact is a meter per second will melt the wire.

    seems trivial at first, but is significant .

    Sophie often criticizes the idea of electrons "whizzing around a circuit"
    and rightly so for they drift along a quite liesurely pace.
    per this physics course

    #10 copper wire carrying 15 amps has electrons drifting at velocity of 0.28 mm (0.011 inch) per second.
  6. Jul 30, 2012 #5
    I didn't just hear it here though(about electrons not really moving that much). One of the pappers i read about it says thats one big misconception taught to students. His papper claimed that the electron within the wire just bunlde up in spots, and the actual current is passed through the electric field + the magnetic feild.

    His paper said some electrons do move, but that it is not a flow of electrons threw a wire, its the flow of an electric field.

    If possible, i'm seeing now it may be hard to get my answer, because i'm gonna end up with lots of people saying different things.

    Its weird, on a subject that we should already know, even different scientists will have different answers. I'm going to check out some of the links, read some more, and come back with more ?'s eventually.

    Thank everyone for your replies. Like i said, i don't want the simple view, i want the view of what really goes on. I love learning about particle interactions, so this is just hobby lerning, just out of interest.
  7. Jul 30, 2012 #6
    Whatever is said about electrons not actually moving through the wire in case of electricity is absolutely wrong. Consider a simple circuit of battery connected with a wire. For current to flow, electrons actually have to be displaced from one terminal to another. Otherwise there will be a huge accumulation of electrons in one terminal of the battery.
  8. Jul 30, 2012 #7

    jim hardy

    User Avatar
    Science Advisor
    Gold Member

    what a refreshing post !

    I have a 1922 textbook that uses the water in pipes analogy. That author is careful to address electron velocity, treating electrons like a hydraulic fluid that moves slowly but transmits pressure quickly. Then he explains that conventional current would be just positive carriers moving the other way , so a simple sign change makes them equivalent.

    So - that mental model will get one a long way toward being able to work with practical electric machines and electronic devices.
    It works well for vacuum tubes and that's surely why the British call them "valves". It has served me well for a half century even with transistors.
    But one must accept that it's an analogy, and there are other schools of thought.
    And one MUST be conversant in terms of BOTH electron flow AND conventional current flow, so get used to making that mental swap.

    Like you i once read a statement that the energy actually moves not through the conductors but through the fields surrounding them.
    That is counterintuitive to me, whose first experience with electricity came ~1947 when i was still in diapers and did the toddler's "hair pin in the light socket" experiment .
    I still remember that sensation of red hot metal searing my thumb, and that energy was clearly deposited INSIDE the metal bobby pin... from where it conducted into to my thumb by simple molecular motion.

    So i just accept that there exist people from those other schools of thought whose understanding of electrical phenomena involves math equations that i do not grasp.
    I hope you keep us posted on your explorations.
    Perhaps you'll teach me about Maxwell's equations - i need them in simple physical terms.

    old jim
  9. Jul 30, 2012 #8
    Jim! I'm glad you had survived the shock, you jolly old man.

    Well you know what? Energy is always carried by the photon particles when its not electricity. When you get a field around a charge, its just the distribution of virtual photons. When you bring another charge in the vicinity the two charges can interact with each other through "real" photons. They are real cause they have this measurable effects of energy loss as the two charges attract or repel.

    In case of simple resistor the electrical energy is carried by electron's velocity. When it loses energy through collision it generates heat. In transmission lines or antennas the effective electron displacement is zero for sinusoidal current, but energy is emitted due to electron oscillation and it goes on from one place to another in form of photon particles, which we call em waves.
  10. Jul 30, 2012 #9

    jim hardy

    User Avatar
    Science Advisor
    Gold Member

    so just as the equation describing propagation of a sound wave thru water in a pipe is quite different from the equation describing mass flow of the water itself,

    equations describing propagation of electrical energy along a wire are quite different from those describing drift of electrons along it.

    i thinnk that distinction is not emphasized in today's curricula
    as well as it was in my 1922 textbook.

    I just opened my 1901 textbook(Sylvanus P Thompson) and there's a whole chapter on it.

    Thanks khold.. it's coming more clear.
    Back to the future...

    old jim
  11. Jul 30, 2012 #10
    @jim - I've known that the concept of electricity and electromagnetic waves go hand in hand when looked from classical viewpoint. But little is explained or talked about the quantum mechanical viewpoint in conventional books. However, being in the field of quantum electronics, I know how "current" flow is actually produced microscopically. But, I was detached from the in depth study (quantum mechanical viewpoint) in case of electromagnetic waves. However I thought something out in this thread.
  12. Jul 30, 2012 #11

    jim hardy

    User Avatar
    Science Advisor
    Gold Member

    you are way ahead of me.

    speed of sound in a medium is (function of compressibility and density)1/2
    that one i'm okay with

    and speed of light in a medium is ( function of permittivity and permeability) 1/2
    that one i accept as not meant for children of the lesser gods
    fields was a course in which i did not do well.

    So excuse me if i take a while to digest your posts.

    somehow they all have to relate back to a proclivity for inertia, and sponginess.

    old jim
  13. Jul 30, 2012 #12


    User Avatar
    Science Advisor

    Although we like to think of electrons as little balls with negative signs on them, I doubt if anyone actually even knows if an electron exists as an individual object or if it is a wave or if it is a disruption in space-time or something else entirely.

    We don't know if they always stay in the same form, if they are all the same or if they sometimes split into smaller bits.

    So, it seems a bit strange to be talking about how they travel through wires as if we knew everything.

    I do know for a fact that the thinnest of hairline cracks in a printed circuit board track will stop a current completely. If it was an E/M wave, wouldn't a hairline crack be a trivial obstacle which could be jumped with ease?
  14. Jul 30, 2012 #13
    That is a classical way of drawing an analogy with familiar objects. In reality elementary particles like electrons, photons etc. can not be correctly described by any classical object.

    I don't know if by "individual object" you mean individually detectable or impossible to be broken down to anything smaller. But the answer to both question is yes.

    The best ever description of standard model is given by quantum field theory (all particles are different operators operating on some common field). There is yet another unproven theory that those particles are made of string. The quest is probably endless.

    But let me ask you a simple question. When you look at a ball do you look at a solid sphere or you look at a collection of atoms which has a spherical shape? Its much more easier to just talk about things in the way they are seen easily. But that does not mean they are ultimate answer. For the time being we know with greatest detail that it is some quantized field.

    Electron is a stable particle in the standard model.

    Electrons are not E/M wave(classically), but photons are.
    However, your PCB crack is big enough for electrons to jump from one side to the other. For quantum mechanical tunneling you got to have air gap in nanometer dimension.
  15. Jul 31, 2012 #14

    jim hardy

    User Avatar
    Science Advisor
    Gold Member

    @ chris arnold

    cc: khold and vk6

    you might like this site

    my old text by Sylvanus P Thompson (which speaks of JJ Thomson and Nikola Tesla in present tense)....
    That was written just 4 years after Thomson's experiments with cathode rays where he measured charge to mass ratio of his "corpuscles", later named "electrons".

    Interestingly word "electron" does not appear in my 1901 textbook.

    Anyhow - my point is
    if you figure out just what electricity is
    please tell me.

    We can observe how it behaves
    and make mental models of things that would behave same way
    and make interesting machines using those models for thought tools
    and earn a good living with what we have convinced ourselves that we know
    but i dont see that we're much closer to answering your basic inquiry than we were in 1901. Compare Sylvanus Thompson's 1901 paragraph to AIP's 1997 one, both above.

    perhaps the highest purpose of education is to make us appreciate how little we really do know.
    great topic my friends

    old jim
    Last edited: Jul 31, 2012
  16. Jul 31, 2012 #15
    One of the things i read that paper stated that the proof electrons do not flow, 1 out of five reasons, is that in transformers, the two coils do not touch, yet the energy gets threw, and electrons cannot jump from one conductor to another.

    Check this papper out, it sounds good, but i don't have the education to decide that, is this papper worth me trying to grasp.

    http://www.scribd.com/doc/87016180/Electricity-Misconceptions-Sefton [Broken]

    As for photons, thats the theory. The electromagnetic wave.
    Last edited by a moderator: May 6, 2017
  17. Jul 31, 2012 #16
    I'll just try to refute Prof. Sefton's arguments one by one:

    1. "electrons are too slow to carry current."
    It is indeed true that electric field does not push electrons as depicted by many textbooks(It just arises due to the distribution of electrons). It is the imbalance(note I dont use "difference") in the distribution of electrons at various points of the circuit that makes the electrons flow.
    The author makes a very common mistake here. The electric current should not be compared with the amount of charge that flows, but the amount of pressure that the flow generates. If you want to calculate how many electrons have passed through the bulb, the formula given by the author is indeed useful, and the number is very small. But when you think about pressure(imagine electrons as incompressible fluid), the change in pressure moves immediately(in theory, in reality it moves with the speed of light). There is a whole lot of discussion here which might help you understand the concept.

    2. "in ac circuits electrons dont flow but jiggle"
    True. Author has mentioned "jiggle", which means the net movements of electrons are zero in a cycle. But the average current in ac circuit is also zero. Thus no conflict. If you look at the instantaneous value of current again use pressure analogy (charge/time) and see that the instantaneous movement of electron is also correlated with the current flow.

    3. The circuit provided by the author is simply wrong. If you create the second circuit the bulb will not glow in the first place(no current flow through secondary). If you replace the dc source with ac source the bulb will glow and dim periodically. But in case of transformer the electrons oscillation energy is converted to magnetic energy and then again converted back in secondary.

    4. yes, if you think closely they do bring back energy in the retrun wire(dc) (However they loses all energy when they finally reaches the source back again). But the important thing to remember here is the energy dissipation. You dont want electrons to lose energy very much while going into/out of the load and use low resistance wire. Most of the electrons energy is dissipated in the load and it has high resistance. Energy dissipation has nothing to do with the current direction, otherwise ac source wont heat up resistors.

    5. author is correct in stating potential energy resides in the arrangement of the whole system. However when one lifts a rock we usually measure how much length the rock has been lifted w.r.t. the earth, not how much length the earth has backed off from initial system. Same goes here. We see the metal atoms as fixed framework, and calculate the relative motion of electrons w.r.t. that frame. It could be already seen that the motion of earth or metal frame is trivial due to their physical property and thus duly ignored here for the sake of brevity.
  18. Aug 1, 2012 #17


    User Avatar
    Science Advisor
    Gold Member
    2017 Award

    This is where the circuit and the hill are hard to equate in many people's minds. Electrical loads and sources are equivalent of elevators and water wheels while the wires are the equivalent of smooth horizontal shelves - as the loads move along these shelves, no energy is transferred. The immediate reaction for most people seems to be confuse the wires with the down-hill bits (because of the physical layout of the circuit and its mechanical analogue).
  19. Aug 1, 2012 #18

    jim hardy

    User Avatar
    Science Advisor
    Gold Member

    you know, we may have overdone it for the original question of what goes on in a battery....

    Sophie your shelf analogy i really like, it is a nice picture to relate 'potential' and 'gradient' to something you can see and feel.

    Mr Chris i admire your curiosity and desire to understand..

    you're exactly right that's how things dissolve, the molecule splits into parts . When the atoms separate and acquire a charge they get called ions.
    An ion can be a single atom, like salt which splits into sodium and chlorine ions, or a part of a once larger molecule like sulfuric acid H2SO4 which splits into H+, H+, and SO4--.

    Indeed the ions can migrate slowly through the water and inside the battery they do just that. That's also the basis for electroplating.

    i made a couple false starts trying to explain this and kinda realized i'm just not a chemist.

    But dont despair - i found a good link , just below.....

    it's more like moving the electrons into a position where they can make a quick score.
    You squeeze them into the SO4-- ions in the battery acid, and those ions would very much like to mate with lead or lead-oxide atoms in the plates to make Lead Sulfate . By doing that they release energy....but the ones at pure lead plate have to shed electrons , and the ones at lead-oxide plate have to acquire some..
    The electrons* that get shed at the pure lead plate come back to the lead-oxide plate through your car headlamps or radio where they give up the energy .
    *(more precisely, electrons identical to them, it takes weeks or years for them to travel the whole external circuit)

    That's why specific gravity of electrolyte tells you state of charge - if the SO4 is in the electrolyte the battery is charged, and if it's in the plates the battery is run down. SO4 is heavy so raises specific gravity of electrolyte.
    {digression - Hmmm "Where has all the sulfate gone, long time passing?" never mind, you had to be around in the sixties... word pictures are soo hard - }

    See if this helps any it has some drawings that helped me.


    Lastly - to your desire to continue learning
    There's a physicist's approach to the world
    and there's a practical guy's approach.
    Many practical guys go on to become physicists, indeed i went to high school with a prodigy who was both by age seventeen.
    But i am a plodder.
    and plodders need to start simple and build their knowledge at their own pace. Distant drummers and all that...

    As i said earlier,
    I got through the 'earn a living' phase and am still learning to this day. But i doubt i'll ever make physicist grade.

    Here is an old Navy training text . Navy's training produced a lot of very competent people , and is very similar to the head-start i got from an old seasoned merchant mariner. I'd have probably not have made it through engineering school without his tutelage.
    Perhaps it'll help you in your studies.

    http://www.rfcafe.com/references/electrical/Electricity%20-%20Basic%20Navy%20Training%20Courses/electricity%20-%20basic%20navy%20training%20courses.htm [Broken]

    with respect, sir, i hope this helps.

    old jim
    Last edited by a moderator: May 6, 2017
  20. Aug 1, 2012 #19
    back to the OP question ive always found the best way to visualise what is happening in a real world concept is a pea-shooter full of peas, we will say that the peas are Electrons and for the analogy purposes are in single file filling the pea-shooter end to end.

    In D.C. the attraction from negative to positive is like pushing a pea in the negative end and irrespective of length of the pea shooter the pea at the opposite end drop out almost instant, now repeat this and what you find is a slow migration of the peas but an instantaneous response over the distance.

    In A.C. the same thing happens but reverses respective to the frequency now the weird thing about A.C. is if you think about the centre pea all it does is move left and right repeatedly and never really going anywhere.

    Conclusion .... Electrons in D.C. migrate at a slow pace while the effect can be close to speed of light (propogation of the electro-magnetic field)

    .... Electrons in A.C. ocillate back and forth while the effect of them doing so again is close to light speed.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook