dexterdev said:
Hello pf,
Electrons are the charge carriers in metal conductor. while explaining about the fact the fact that electric field inside a conductor is zero, there is a depiction showing charge moves to surface (+ve and -ve charges to extremes of metal conductor surface) in emt books of sadiku and griffiths etc. ok -ve charge refers to electrons , but what about +ve charges? are they immobile ions. please help..
This is not true. The charge carriers in a real metal are not always conduction-electrons. Sometimes, the charge carrier in a metal is a valence-hole.
My favorite reference on solid state is:
“Introduction to Solid State Physics 7th Edition” by Charles Kittel (Wiley, 1996).
On page 167 (Chapter 6, Table 4), there is a list of metals, their Hall-coefficients and their free-carrier types. Most metals have conduction-electrons as carriers. Aluminum and indium have valence-holes as carriers. Both aluminum and indium are true metals and good conductors.
Valence-holes carry electric charges in some trivalent metals. However, the carrier-type of beryllium was left out of Table 4 of Kittel. I don’t know why. Beryllium has a positive Hall-coefficient, so one would think that it is a hole-metal.
Note that in all these cases of “true metal”, electrons really carry the electric charge. Both conduction-electrons and valence-holes are examples of quasiparticles. Both conduction-electrons and valence-holes are composite systems made of true electrons.
Ions don’t usually carry electric charge in solids. I will not discuss those anomalous examples where ions do move in solids. You will recognize them when you read about them. Moving ions do carry electric charge in electrolytes and in plasmas.
These quasiparticles behave differently than the electrons would behave in a vacuum. For example, both conduction-electrons and valence-holes have an effective-mass different from the real mass of an electron. Their “particle-like” behavior breaks down under some circumstances.
You shouldn’t think of the conduction-electron as being any more like a real-electron than a valence-hole. Furthermore, you shouldn’t think of the valence-hole as being any less “real” than a conduction-electron. This is why I always prefer to use an adjective to qualify the word electron or hole.
Kittel describes the measurement of the Hall-coefficient. If the Hall coefficient is negative, the free-carrier is a conduction-electron. If the Hall-coefficient is positive, the free-carrier is a valence-hole.
Some other group had this discussion. However, I particularly like the point that this poster made.
http://physics.stackexchange.com/qu...all-effect-ever-show-positive-charge-carriers
“There are two essential facts that make a hole a hole: Fact (1) The valence band is almost full of electrons (unlike the conduction band which is almost empty); Fact (2) The dispersion relation near the valence band maximum curves in the opposite direction to a normal electron or a conduction-band electron. Fact (2) is often omitted in simplistic explanations, but it's crucial, so I'll elaborate.”