Describe Elecrons Behaviour/Motion In AC & DC.

Discussion in 'Homework Help' started by khaqan_shati, Jul 24, 2005.

  1. khaqan_shati

    Thread Starter New Member

    Jul 6, 2005
    2
    0
    AC and DC are Two different types of currents . ALternating and direct respectively.
    is there any difference in electron's motion or behaviour in AC n DC .
    as AC is alternating means current changes its direction ,then is it means that electron's motion is reversed as current is flow of electrons. or this is wrong approach . if so plz describe wat is actually happening to electron in AC n DC
    waiting for quick response .
    u can mail me too : khaqan_shati@hotmail.com
     
  2. Brandon

    Senior Member

    Dec 14, 2004
    306
    0
    AC & DC are not that different in terms of electron flow because electrons are not flowing when you get power from the line, rather the charge is flowing through the medium created by the valence electrons if I rememebr correctly. Actually, the electrons move in the opposite direction of the flow of current at a very very slow speed, the electron drift. Its so slow that if the electrons did generate power it would take a few minutes for a light to turn on when you flip the switch. You got to hate standard education.. I wish they would just teach the right thing from the get go.

    If we talk about charge, in DC, the charge stays the same, keep flowing in th same direction and at the same rate.

    In AC, the charge keeps switching directions.

    As to the electron flow, I belive in AC they basicly just shimmy back and forth like they are doing the twist.

    Someone a little more fresh with their fields and waves will probably be able to elaborate much better.
     
  3. Dave

    Retired Moderator

    Nov 17, 2003
    6,960
    143
    Some time back I posted the following explaination of current flow in conductors, thought it may be of interest here:

    If you look at the speed at which free electrons randomly move between atoms in a conductor, it is around 10^6 m/s dependant on certain factors such as temperature. Now if we apply an electric field to the conductor these free electrons will experience a force which accelerates the electrons in the opposite direction to the field. They collide with the atom nuclei and and are deflected from their flowpath, loosing energy with each collision (this energy loss is the heat we feel when we hold an insulated wire which is carrying a current). What we actually now have on a macro scale is a steady drift velocity superimposed over the random movement of the electrons on the micro scale. The current in the conductor is defined by:

    I = ne x VdA

    Where:

    n is the number of atoms per cubic metre
    e is the electron charge
    Vd is the drift velocity
    A is the cross-sectional area

    Although the above equation requires you to deal with a vector product, it is simple to reduce the equation to the form:

    Vd = J / ne

    Where:

    J is the current density

    Using typical values, you will see that the drift velocity of the current in the conductor is only around 0.22 mm/s - this is incredably slow!! If you don't belive me try putting typical values into the above equation.

    From a strict Physics and Electromagnetics sense, current is a vast quantity of rapidly moving electrons upon which an incredably slow drift velocity is imposed.
     
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