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What is electricity?

  1. Jul 15, 2009 #1
    So I have these huge doubts on the deep nature of the force we refer to as "electricity" or "electric current" in our daily lives.

    I want to know exactly what it is and most online resources are very circular (electricity is electric current which is electric fields which is electricity etc.)

    It's difficult to know what to ask first but let's devise a simple practical example for starters.

    When I plug my, say, electric fan to the outlet and turn it on, is it a bunch of free electrons that pour into its electric motor and power it? I think it's not, but then what is it? Is it an excitation of electrons that passes on as a wave (more like it)?

    Well I have many more questions but they'll only pop out when the dialogue is started! Thank you!
  2. jcsd
  3. Jul 15, 2009 #2


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    Staff: Mentor

    Welcome to the PF. That's a very broad question. Perhaps it would be better if you read through this article:


    and told us specifically what you find confusing. Thanks.
  4. Jul 20, 2009 #3
    Electricity is a very broad topic. However, the fundamental thing to remember is that it is an electro-magnetic wave - i.e. it travels quickly. Energy is transfered from point a to point b by this electro-magnetic wave. For electricity to travel there must be a ring or circuit. This is because the electricity produced by moving magnets follows a circular path. Voltage and current are a very convient means to analyze circuits but break down on even simple things like a plug - i.e how does current jump from the socket to the plug.

    Kind regards,

  5. Jul 20, 2009 #4
    Well at its core 'electricity' reflects the fact that atoms are made of charged particles, the important one for electricity being electrons. Now in substance that are metallic these electrons are not really associated with any one atom and have a certain freedom. In addition every charged particle emits an electromagnetic force of the form [itex]\frac{kq_1q_2}{r^2}[/itex] on other charges. From these simple facts (more or lesss) we get the richness of electricity.
  6. Jul 20, 2009 #5
    In terms of electric current, when you plug in your fan into the wall the circuit is completed, meaning that there is a flow of electrons through the circuit. In the case of a household it is AC (alternating current) meaning that the electrons go backwards and forwards real fast instead of flowing in one direction.

    The flow of current is associated with magnetic fields. When there is a current flowing through a wire, there is a magnetic field expanding in concentric circles around the wire. This magnetic field is utilised in an electrical motor to provide a force.

    An electric motor is composed of a coil of current carrying wire in a magnetic field (two magnets on either side of the coil). When electricity is running the magnetic field of the wire interacts with the magnetic field of the magnets and causes the motor to spin. This motor is what is used to spin the fan.

    Any of this can be expanded on so feel free to ask questions :)
  7. Jul 20, 2009 #6
    Last edited by a moderator: Apr 24, 2017
  8. Jul 21, 2009 #7
    The word electricity is a general name for the whole process, as when we say that an appliance uses electricity.

    Current is a specific measurement, the rate at which electric charge flows, so if 100 coulombs of charge were to flow past any given point in 25 seconds, the current would be 4 coulombs per second, which is called 4 amperes.

    It's true that metal wires have a lot of free electrons, but then they have to be caused to move. When you plug it in, the voltage produces a directionality that is similar to the sense of up and down in a gravity problem. As gravity makes it the spontaneous direction for a ball to roll downhill, the applied voltage makes it become the spontaneous direction for the electrons to move in a certain direction.
    Last edited: Jul 21, 2009
  9. Jul 21, 2009 #8
    Rightfully electricity is nothing more than the ways through which we can observe it, e.g. generating light, driving engines, heating and so on. The theory of electromagnetism is just a framework that exists in our heads to help us make sense out of these different phenomena. Therefore one should be careful to say that a different phenomena for sure are manifestations of something fundamental called electricity (although the evidence supporting the claim is overwhelming :smile:).

    Let's say electricity is the knowledge of how charges interact. But since we know of many different particles carrying charge, isn't electricity then just a property of matter rather than something real in itself?

    My point is: the what is question can never be given an indisputable answer because it's so dependent on our current knowledge and our somewhat arbitrary way of expressing physical laws.
  10. Jul 21, 2009 #9
    It's good to have such doubts/questions..that's sometimes how progress is made when someone realizes current understanding is limited/incomplete/superficial or whatever.

    In the the case of electricity, it is quite amazing!! While free electrons are involved it's more than just that: Power is volts times amps, P =IE, so making EITHER current or voltage higher, or both, produces more power. If either is zero, then no power!!! And it DOES take a LOT of electrons: from q = it, you can figure how many electrons (one coloumb) flows for one amp for one second: about 1018 !!!!!!!!!

    Electric power is a means of converting either mechanical energy (alternator or generator) or chemical energy ( a battery) into a convenient form for wide application.
  11. Jul 21, 2009 #10
    Stick with peer-reviewed sources, such as university web sites. Avoid self proclaimed experts.

    Last edited by a moderator: Apr 24, 2017
  12. Jul 21, 2009 #11


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    Science Advisor

  13. Jul 21, 2009 #12
    It's basic EM. Any determined learner who made it through second year physics (or self-taught) could provide a correct and helpful answer to such a question.
  14. Jul 21, 2009 #13


    Staff: Mentor

    A person may be an author of peer-reviewed manuscripts. Then those manuscripts are peer-reviewed sources. The author himself is not a peer-reviewed source, and neither is his or her website.
  15. Jul 21, 2009 #14
    Thank you all for the replies! I've been having time constraints to reply.

    But one main question is in my mind: if free electrons are jumping from atom to atom, then at some point some atoms will start running out of electrons? If the elements' chemical properties are defined by the amount of electrons (among other things), they if they lose electrons they will become freaks?;)
  16. Jul 21, 2009 #15
    A good question but unfortunately I can't think of a good way to answer it in an explanitory way... How good is your math (calc/DE's is all you really need to tackle this one)?
  17. Jul 21, 2009 #16
    the atoms dont actually lose electrons. in the metallic bonding model the metallic atoms bond by rejecting their valence electrons. This results in a veritable sea of electrons that is free to move through out the metal structure. Incidentally this is the main reason for many of metallic objects properties such as being good conductors of heat and electricity and lustrous look.

    When an electrical current is flowing through a metal the electrons are getting moved around the circuit. In terms of plugging in your fan, just as many electrons come out the plug as go into the plug. This means that the overall amount of electrons stays constant within the circuit.

    there has always been an analogy of electricity being like water in a pipe. Electrical current is like water flowing through a pipe. The same amount of water will come in the pipe as goes out the pipe. the amount of water passing a pipe at any moment is the rate of flow. in electricity the number of electrons passing a point every second is measured in amps. One amp is coulomb of elevtrons per second. A coulomb itself is a set number of electrons, akin to how eggs often come by the dozen. The number of electrons in one coulomb is 6.25 x 1018.

    The voltage is sometimes explained as the pressure of the water in the pipe. The voltage, which is also called the potential difference is what essential the driving force behind the electric flow. Just as a mass has a gravitational potential when raised up in the air, the voltage is the electrical potential in a circuit. One of the best definitions of voltage I've come across is:

    If it takes 1 joule of energy to move 1 coulomb of electrons through a circuit, then the voltage of the circuit is 1 volt.

    this means if you move 1 coulomb half way around the circuit 1/2 a volt has been used.

    hope this helps :)
  18. Jul 21, 2009 #17
    Well there's no "analogy" the equations of classical EM WERE the equations of fluid dynamics. However, this isn't actually the correct picture. What you're presenting here is essentially the drude model which does not correctly predict a great many things in condensed matter (like thermoconductivity)
  19. Jul 21, 2009 #18
    this is true, however i find it most helpful to explain it this way. heck of a lot easier to understand than some other ways i've see
  20. Jul 21, 2009 #19
    I think the complexity to utility trade-off is better served by a sommerfeld electron in a vanishing potential.
  21. Jul 21, 2009 #20
    OK the water through pipe model is quite helpful. But I would like to illustrate the matter a little further.

    For instance, our classic copper wide. Its made of copper atoms, plus impurities which can be ignored for the moment.

    A copper atom contains 29 electrons, distributed in four layers 2, 8, 18, 1.

    So we have Cu(2,8,18,1) or Cu(29) to represent a copper atom in plain text. If the nucleus is considered, it contains 64 neutrons and 34 protons (correct me if Im wrong).

    So we would have gazillons of atoms of copper bound to eachother:

    29P+64N+29E = atom of copper x gazillions.

    This mass of 29P+64N+29E would then, according to the properties of free electrons found in transition metals (why is that?) be constantly losing and gaining one or more electrons from their Copper neighbors, but each atom would always maintain 29 eletrons around their nuclei, right?

    Then what exactly is being produced at my local powerplant and what is my computer "gaining" that powers it? Its not being fed with excess electrons, that I know. It's being fed with "electric charge", which is made of nothing, apparently!

    Apparently, after a 20 minute pause from last paragraph, I can only assume what being fed to my computer is, basically, "INFORMATION". The electrons of my lithium-ion batteries are being reprogrammed to contain an unstable amount of "charge" which does not occur without the rotor at the local hydroplant convincing my copper atoms in its motor somehow that their charge changes... wait Im onto something Im having an insight here but I lack more concepts, I lack more knowledge. Please analyse the babble in this paragraph and provide some info on what this "charge information" is....
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