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

What make the electrons to move in conductor with current?

  1. May 10, 2007 #1
    What make the electrons to move in conductor with (direct) current? Is the magnetic field exciting the electrons or what? Please if you know explain deeply.
  2. jcsd
  3. May 10, 2007 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    Look at the Lorentz force equation.


    E is the electric field provided by whatever power source. So where do you not understand the mechanics here?

    If I may make a suggestion. You have a series of rather basic questions that require more than just a question and answer session like this. I strongly suggest you open an intro physics text, such as Halliday and Resnick, or even some high school physics text. Or look at several website that provide really basic intro physics, such as the http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html" [Broken] website. This is the most effective way to learn stuff systematically, especially on the questions that you have asked a few times on here.

    Last edited by a moderator: May 2, 2017
  4. May 10, 2007 #3


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Firstly, current is the actual flow of electrons or charge. If we take a microscopic view, then we can relate the current (I) to the number of free charge carriers (n), the individual charge of these charge carriers, which in the case of a wire is e, their drift velocity vd and the cross sectional area thus;

    [tex]I = neAv_d[/tex]

    Or more generally we can define the current density [itex]\vec{J} = ne\vec{v_d}[/itex] and represent the current through a surface [itex]\vec{S}[/itex] thus;

    [tex]\int_{S}\vec{J}\cdot d\vec{S}[/tex]

    What makes the electrons flow, is not the magnetic field, but the electric field created by the potential difference induced across the conductor (by a battery for example). So roughly speaking when you place a potential across a wire, the electric field at the end of the wire changes, this causes the electrons at the end of the wire to move (recall F = qE). Once these electrons have moved, they change the electric field experienced by the neighbouring electrons, which as a result feel a net force causing them to move, thus again perturbing the field for their neighbouring electrons. This affect is repeated down the whole length of the wire, each electron perturbing the field of its neighbours causing it to move, like a line of dominos. This is the reason why signal transmissions is electric wires are significantly faster than the actual drift velocity of the individual electrons. Although the actual electrons 'drift' relatively slowly, the perturbation in the electric field is transmitted down the wire at virtually the speed of light.

    I hope this was helpful :smile:

    Edit: Zz beat me to it :sad:
    Last edited: May 10, 2007
  5. May 10, 2007 #4
    Thank you very much, but I still can't understand:frown: . Can u explain simpler than this. Why the electric field makes them move, is it excites the electrons or what? Is the electric field fixed or it is moving with the electrons? Thank you again.
  6. May 10, 2007 #5
    When you apply an E-field onto a free electron, this electron will feel a force equal to F=qE (q is the electron charge). Whenever a force is exerted on such a free electron, it will move. To calculate the velocity and trajectory of this electron motion caused by F=qE you need to integrate this equation with respect to time once, to get the velocity and twice , to get the trajectory.

    This is basic classical physics. You should study this stuff from a good book like Zz has already told you ! The hyperphysics website can help you as well.

  7. May 10, 2007 #6
    Ok, thank you very much, now I understood it, but why (for ex.) the magnetic field is not exerting force on the electrons?
  8. May 10, 2007 #7
    What magnetic field ? The external applied field onto the electrons is an electric field.

  9. May 10, 2007 #8
    Yes, but also that electric field creates magnetic field like the magnetic field which is creating electric field.
  10. May 10, 2007 #9
    So how that is going? First the electric field force makes the electrons to move, so did the electric field moves with the electron together?
  11. May 10, 2007 #10
    For direct current, the time derivative of the electric field is zero (by definition). Therefore, there is no displacement current, and the only source of magnetic field is the current itself.
  12. May 10, 2007 #11
    But that is why i asked you about the magnetic dipole thing. Why did you not answer to my question ?

    The electric field does not generate a magnetic field, the electron current DOES, as described by the laws of Maxwell. Do you know these laws ? Do you know the concept of displacement current etc etc ?

    You need to study those introductory concepts.

  13. May 12, 2007 #12
    Can somebody explain how does the current is gained with electromagnet induction and what happens inside of the conducor when you move the magnet among the conductor? Thank you very much. Please if you can explain with simpler words and simpler text.
  14. May 12, 2007 #13
    I think what your fundamentally asking is... if the electricity is electrons moving... then "What is voltage?" Well think about it this way.. the magnet moves, because of this relative motion between the magnets and the electrons, the electrons feel a force. Dictated by the laws that are fundamentally stated in any intro physics textbook. These laws dictate the movement of electrons in the conductor.

    Now... since the electrons feel this force and move from their native atoms, there is now a deficiency of electrons in that atom, so.. the atom becomes +ve. So... now there is a potential difference between this atom and the neighboring atoms. This is the potential or voltage... Now... you move enough of these little critters away, then the force becomes more profound.

    As to why these forces themselves exist, well they are fundamental forces and thats how nature works, or at least thats what we have observed..

    If you are still interested in knowing why!? then your out of luck... physics hasn't even finished "completely" explaining the how yet, so the why!? is a question for when the hows been solved..

    So, I hope this explains it...

    But.. Im not sure of this explanation completely yet, tried finding these answers myself, this is the explanation i came up with...
    so... Hmmmmm.... Am I right?
  15. May 12, 2007 #14
    Exacly I think like you, but I wanted somebody to confirm me. Thank you very much, you answered all of my questions with one post. Just I wanna ask, not all of the electrons of the atoms are unbounding right?
  16. May 12, 2007 #15
    "Unbounding??" hmmm... well Let me just tell you that you are not using the right terms... And this can cause confusion because specific terms, mean specific things in physics and using them will nilly can cause problems.

    Anyway... no not all of them move, only the outer, "valance" electrons... But let me just ask you straight up... What are you getting at?
  17. May 12, 2007 #16
    Look the electrons are kinda connected with the protons, they are holding each other (opposite charges), so that's why I said unbound. Ok, I understand all of your explanation.
  18. May 12, 2007 #17
    In a DC circuit, mobile electrons flow in response to a uniform electric field created by a gradient in surface charge distribution over the outside of the circuit.

    See http://galaxy.cofc.edu/circuits.html for simulations and some discussion, although you won't find much about this in traditional introductory textbooks and not much more at the graduate level. It's a shame since is a simple and correct model.
    Last edited by a moderator: Apr 22, 2017
  19. May 13, 2007 #18
    But I can't understand that, from the one side there are moving valence electrons and from another not (potential differences). When you move the magnet, you move it from both sides, how is that possible? PLease explain. THank you.
  20. May 13, 2007 #19

    Doc Al

    User Avatar

    Staff: Mentor

    I'm having a hard time understanding what it is you are trying to ask. Realize that electrons in a conductor are free to move when subjected to an electric field. Are you trying to understand how an applied voltage source (battery) creats an electric field in a conductor?
  21. May 13, 2007 #20
    I am trying to realize when moving the magnet among conductor and creating voltage, from the one side there are valence electrons which are moving (- potential), and from the other there are not moving electrons (+). Why on the + potential there is not moving electrons, when the magnet is moving on whole conductor?
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook