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Electric current question

  1. Mar 13, 2009 #1
    Okay, I have another question. I understand about protons and electrons I think. When a proton doesn't have enough electrons around it, that's considered a positive charge, correct? And when a proton has too many electrons, that's a negative charge, correct? And like charges repel, and opposite charges attract. And electric current is the movement of electrons from a negative charge to a positive charge, correct?

    So when current moves through a wire, for instance, is it the same electron that just travels the length of the wire (like a subway traveling through a tunnel), or is it a chain reaction where the first proton in the wire attracts an electron, which makes it negatively charged so an electron is given to the next proton, and so on down the length of the wire? Or I guess maybe the positively charged proton on the positive end takes an electron from the first proton in the wire, and the first proton then takes one from the next proton, and so on down the line? Or am I way off?

    I'm also a bit confused about batteries. The positive end of the battery is full of positively charged protons and the negative end is full of negatively charged protons? Or am I way off? How does the chemical reaction in the battery create positive and negative charges?

    I know these questions are probably frustrating, so I appreciate you guys taking the time to help an inquisitive person out. :)
     
  2. jcsd
  3. Mar 14, 2009 #2

    Dale

    Staff: Mentor

    Current is just the movement of charge. The charge carriers could be negative, like free electrons in metal, or positive, like sodium ions in an electrolytic solution.

    That is about right. The drift velocity of an individual electron is on the order of micrometers per second, whereas the current propagates at close to the speed of light.

    Yeah, you are off. The chemical reaction gives energy to an electron, which allows it to push through the circuit and do some work. There is not a net charge stored in the battery, just energy.
     
  4. Mar 14, 2009 #3
    Thanks for the reply, although I'm having trouble following you. lol

    So a chemical reaction in a battery energizes electrons? It's basically just shooting off electrons? Why does it have to have a closed circuit for the electron to be shot out into the wire?

    The electron that is energized forces itself onto the first proton in the wire which causes a chain reaction like I mentioned in my original post?
     
  5. Mar 14, 2009 #4

    Dale

    Staff: Mentor

    Think of it like the wire is a pipe, the electricity is the water in the pipe, and the battery is the pump. There is no more water on the outlet side than on the inlet side of the pump, the pump does not store or create water, it just adds pressure energy to the water. If the outlet pipe is capped then there will be no current, the water will just be pressurized until the pump can no longer push against the pressure and then the pump will stop.

    Similarly with the battery. If there is no place for the current to flow then the electrons will just be raised to a voltage until the chemical reaction can no longer push against the voltage and then the chemical reaction will stop.

    Yes, that is close enough.
     
  6. Mar 14, 2009 #5
    A galvanic cell is an example of a battery. Both solutions are different and therefore have different standard electrode potentials. If you connect them and close the circuit (for instance by using a salt bridge), the potential difference will create an electric field which exerts force on the electrons which will cause them to flow.
    Check this out for a more elaborate description: http://en.wikipedia.org/wiki/Galvanic_cell" [Broken]. Modern batteries may be different, but as far as I'm concerned they all rely on the same principle.

    I wouldn't consider it a chain reaction. Let's take a metal conductor, such as copper. It consists of electrons that move through the material (even when no electric field is being applied). But because of the random motion, there is no net movement of charge. When we would connect a battery to the wire, a force will be exerted on the electrons that are already in the wire, which will cause a net flow of charge (current). So it's not that one electron enters the wire from the battery and kicks the other electrons to produce a current.
     
    Last edited by a moderator: May 4, 2017
  7. Mar 14, 2009 #6
    Hi, hood.... In metals electrons, many electrons are not bound to atoms so ready to move.
    when voltage source is connected, the electric field will exist on the wire, the longer the weaker, because simply put Efield=V/(metal length). The electron will move by this field. now assume that somehow the circuit is open, then these electrons will pile up at one end of the wire, which electrons hate because they repel each other in instinct you know same negative charge so no more electron pile up, meaning that no more current flow. Regarding electron identity I am not sure we can trace that well, because they are not free electron in space but they are in the metal which do not allow individualism but they are characterized more as a wave and more or less in a collective objects. I think this is a close picture under quantum mechanics.
     
  8. Mar 14, 2009 #7
    Okay, that makes sense guys. Thanks!

    One last question. What exactly is the energy that the battery puts out? It puts out an energy that makes the electrons in the wire flow, but what is it? Is it a different energy than the force that makes differently charged protons attract and similarly charged protons repel? Or do we not really know exactly what that energy is?
     
  9. Mar 14, 2009 #8
    I think you're confusing two different concepts, namely energy and fields. It's not energy that makes differently charged particles attract and similarly charged particles repel, it is fields (electric fields in this case). A field describes the force that would act on a particle if such a particle were present. (note: you are talking about similar and oppositely charged protons, but protons always have a positive charge, so there is no such thing as oppositely charged protons).
    If that is what you meant, the answer to your question would be yes; the forces that charged particles exert on one another and the force that acts on the electrons in electric current are both as a result of an electric field.
     
  10. Mar 14, 2009 #9
    Recently people work on battery a lot because of electric car and energy storage in wind energy.

    Battery communicate to outside through metal electrodes so obviously the electric energy is the final output from battery. One electrode has higher voltage marked as "+" or "positive". This voltage in the battery is comes from excess electron accumulation in the "-" electrode, and electron shortage in "+" one, and this accumulation comes from battery chemical reaction.

    People try to optimize chemistry and materials used to maximize battery performance, and USA government promised big prize for the most efficient battery maker. We want light weight and powerful one.
     
  11. Mar 15, 2009 #10
    So batteries put out an electric field, and that's what the chemical reaction does?

    I'm still curious as to what exactly the "energy" that comes out of the battery is. The energy that causes the electrons in the wire to move to one side.

    The current goes from the positive output of the battery to the negative output, right? (or is it the other way around?) So, what is it about the negative output of the battery that allows the electrons "built up" in the end of the wire to come out? If the wire goes from the positive end of the battery to the ground, the electrons stay in the wire. So, what it is about the negative end that allows them to travel? And where do the electrons go once they get to the negative end?
     
  12. Mar 15, 2009 #11

    dpk

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    ihave doubt what is the origin of cosmicrays
     
  13. Mar 15, 2009 #12
    Yes, it does. The chemical reaction 'tries' to reach an equilibrium in which there is no longer an excess of electrons on the (-) side on the battery, and no longer a shortage on the (+) side.

    When you get electrons moving, that's kinetic energy, right? There is a potential difference between the plus and minus side of the battery. You can compare it to dropping your hat, potential energy will be converted into kinetic energy.

    The electrons flow from (-) to (+) and the current goes from (+) to (-) (by convention).

    I believe this has already been answered. Electrons won't all go sit on the end of a wire if you only connect the negative side because electrons repel each other. If you, however, connect the positive side of a battery to the end of the wire, the (negative) electrons will feel a force which makes them flow.
     
  14. Mar 15, 2009 #13

    Dale

    Staff: Mentor

    In a chemical reaction the molecules of the reactants change their configuration so as to result in the molecules of the products. In that process the microscopic electromagnetic fields surrounding each molecule results in work being done on the molecules. Although the intermolecular forces are small and the intermolecular distances are also small there are so many of them that the net work can be considerable.
     
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