help

Discussion in 'General Electronics Chat' started by mikaela, Feb 1, 2005.

  1. mikaela

    Thread Starter New Member

    Feb 1, 2005
    2
    0
    hi! i came across with this question in class and i can't quite figure out the answer. i have looked everywhere but still i have no idea as to the answer. heres the question

    "some of the free electrons in a good conductor move very rapidly at the speed of 10 exp 6 m/s or more. why don't these electrons fly out of the conductor completely?"

    another question i encountered is this:

    " Defend the statement: If there were only one electrically charged particle in the entire universe, the concept of charge will be meaningless"

    i sort of have an idea with the second question but i just want to be sure am right....

    anything that you will have to share is very much appreciated.. thnks a lot!
     
  2. haditya

    Senior Member

    Jan 19, 2004
    220
    0
    to knock an electron out of an orbit one has to provide with energy equal to the energy of the electron(Kinetic Energy +Potential Energy) in the (bohr)orbit..

    the energy of the electron in motion is insufficient to do this
     
  3. Firestorm

    Senior Member

    Jan 24, 2005
    353
    0
    the answer to your second question is in my opinion this:(dunno if its wut u got/ or even right)
    if there was only 1 charged particle then there would be nothin for it to attract or repel to...therefore the particles charge is worthless due to the fact that nomatter where it was it would not affect another particle to the extent to changing it charge wise....hope this helps...

    -fire
     
  4. mikaela

    Thread Starter New Member

    Feb 1, 2005
    2
    0


    thanks a lot for your help... moreover, you did not let me feel stupid for not knowing anything.. unlike others... and that makes a lot of difference... thanks again...
     
  5. Firestorm

    Senior Member

    Jan 24, 2005
    353
    0
    np, im sure no1 here meant to make u feel stupid in anyway but were just clearly explaining the concept...dont hesitate to ask questions because the only real way to learn is to ask them...quote from somewhere i think, just dunno where from...l8er

    -fire
     
  6. vineethbs

    Well-Known Member

    Nov 14, 2004
    56
    0
    ur first question was : why do "free electrons" which move at speeds over 1e6 stay within "good conductors"
    one thing is see here is that , its not just free electrons that move with such speed,in fact by the uncertainity principle there cannot be an exact speed for an electron.
    But since the term free electrons hav come in , i wud like some clarification , the "orbital speed"(there r actually no well defined orbits) can hav such speeds , but a free electron usually is considered wrt conduction processes , during conduction , the free electron has a drift velocity which is usually only a few cm/s .
    the reason that free electrons cannot move out of the body of the conductor is because if an electron goes out the conductor becomes positive this attracts the electron back , so a certain amt of energy called the work function has to be given to the conductor (like cathodes in electron tubes ,or photoelectric effects)to kick the electron out

    the definition of charge is basically made by the definition of the force on the charge , so with one charge there cannot be any force on it ,so i guess FIRESTORM has explained it well :)
     
  7. 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.
     
Loading...