Electron Movement Speed Contradiction?

Thanks TVP, you have cleared up one of those lingering grey areas.

Thanks, guy's. You confirmed what I suspected when I ran up against it in Stan Gibilsco's "Teach yourself Electricity and Electronics". In addition to electrons, current and the ampere. Giblisco sort of wanders into the difference between the electrons and the movement of 'holes'. This is defined as a shortage of an electron. I'm a bit curious regarding how this Holy situation came up?

Thanks,

/Ari (Orpheuse)

See page 14 of Giblisco's book.

And another thing, whilst we are on the electron theme. I always thought that electrons in hard vacuum moved at the speed of light yet electron optic devices use electrodes to 'accelerate' the electrons. Is this just a misnomer or are the electrons really accelerated?

No, electrons don't move through space at the speed of light. They have a rest mass and cannot be accelerated to that speed. You see acceleration of electrons whenever you sit in front of a CRT (old TVs, monitors, etc).

That makes more sense that the impression I had before. In terms of the devices I work with, the electrons must be emitted from a photocathode surface into vacuum at a particular speed then get accelerated by the electrodes towards their destination. I can picture that happening.

There are few questions which always bugged me as far the flow of electrons is concerned in metal.

1) When you say that there are free electrons per atom, then where do they come from? and why do they exist?

2) When electrons move for the current to flow then, isn't it possible that there will be no free electrons at the start point one day?

3) Is conductivity dependent upon the the number of free electrons available?

I might add that all three of the best conductors (Ag,Cu,Au, in that order) have a single electron in the outermost shell. It is that outer electron that is only weakly attached to the atom, and can easily be removed and replaced, thus allowing electrical current. I think it is also significant that all three of these metals are very ductile and malleable, indicating that the electrons are not strongly bound in forming a crystal lattice.

For Q1:

The free electrons ( as well as other electrons in inner orbit ) are available in nature as they are consitutents of an atom. And atoms are formed by Unknwon!

For Q2:

First of all in any case neither there is a producion of electrons nor their consumption.

For understanding consider you are having a round metal strip ( just equavalent to closed circuit as current flows in closed circuits only ) and mark two spots namely 'A' & 'B'. Consider point 'A' is a voltage source where free electrons are liberated from their atom and these electrons are moving towards to point 'B'.

These new electrons have the energy in the form of Drift Velocity. As these new electrons approaches the point 'B' they are bombarding the atoms in point 'B'. Because of this, a new set of electrons ( equal in number ) are liberated in point 'B' from their parent atom. Their positions are occupied by those old electrons from 'A'. And from point 'B' there is no other way around, the released electrons tends to flow towards to point 'A'.

By this, atoms in point 'A' getting their makeup are now ready to release a new set of electons towards to point 'B'. This forward rotation of electrons never stops until there is a voltage source of DC is available in point 'A'.

I hope you not getting confusion too much. If Yes, then it is worth to say that it is not the case in AC.

In AC,

1. at time t=0: 'A' to 'B' & 'B' to 'A' (in clock wise) => Forward rotation
2. at time t=1: 'A' to 'B' & 'B' to 'A' (in anti clock wise) => reverse rotation

and this cycle also continues with availability of AC voltage.

For Q3:

Absolutely. The avialability of free electrons in a metal is termed as resistivity of that particular metal.

for Cu, the resistivity is 1.68x10^-8 Ohm-meter.

Thanks a lot.

But, there are still some doubts.

- Are those free electrons live ouside the normal orbit of the atom? What force keeps them attracted towards the atom, even when atom has all the necessary electrons in orbit to keep it stable.

- When we say that the current is flowing then actually a charge is being transferred in some specific time. And electron itself is charged particle. So while drfting is it that the electrons are giving away their charge to neighbouring elecrons, then in such case what happens to those electrons (without charge)

Please answer.

The electron (normally only one) that is easily removed from the atom is the one in the outermost orbit, and which because of that orbital distance has the weakest attraction to the nucleus. It IS a normal orbit, with the electron attracted by its opposite charge to the nucleus, more strongly than it is repelled by the other electrons of the same atom. Once that electron has been removed, the remaining group of particles is no longer an atom, but is an ion having a net positive charge, which will attract any nearby electrons.

In a wire carrying a current, there is an electric field pushing/pulling all the electrons in one direction, so an atom that loses an electron and becomes an ion will quickly acquire a replacement electron from a neighboring atom, and once again become an atom.

The electrons never lose their charge; it is their movement that constitutes the electric current.

In my experience, the term stable is normally applied to nuclei, not to atoms. An unstable nucleus is one that can lose a proton or neutron, thereby becoming a different element or isotope.