From Newsgroup: sci.physics

Hi, I was reading an introductory chapter in an electronics book, an
older book (1960's, I think) and it explained insulators, conductors,
and semiconductors in connection with bands of energy states in quantum
theory. He seemed to be saying that conductors allow electrons to easily
move between energy bands, movement of electrons is current, and
therefore conductors allow current.

The part I'm unclear on: when exactly is it that the electron moves from
one part of the conductor to the next, i.e., down the wire? Are we
just saying that, at the higher energy state, the electron will be
moving around the material more often? Or that somehow moving from one
energy state to the other, is movement through the conductor?
--
Christopher Howard
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From Newsgroup: sci.physics

Christopher Howard writes:

The part I'm unclear on: when exactly is it that the electron moves
from one part of the conductor to the next, i.e., down the wire? Are
we just saying that, at the higher energy state, the electron will be
moving around the material more often?

A simple model is that the conduction band electrons are not bound to
any particular atom but are free to move around the crystal in response
to external fields.
--
John Hasler
john@sugarbit.com
Dancing Horse Hill
Elmwood, WI USA
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From Newsgroup: sci.physics

Christopher Howard <christopher@librehacker.com> wrote or quoted:

theory. He seemed to be saying that conductors allow electrons to easily
move between energy bands, movement of electrons is current, and
therefore conductors allow current.

The /energy of an electron/, here, is the sum of its kinetic
and potential energy.

An electron of low energy is bound to its atom because it does
not have enough energy to break free from it just like a frog
cannot leave the Earth because it cannot jump high enough.

An electron of high energy can move away from its atom to neighboring
atoms just like a rocket can leave Earth and fly to the moon.

An /energy band/ is a range of energies.

The /valence band/ is the range of energies of the outermost
electrons of an atom.

The /conduction band/ is the range of energies that allows
electrons to move freely within a conductor.

In a conductor, the region of outermost electrons of one atom
/overlaps/ with the region of outermost electrons of neighboring
atoms, so the valence band and the conduction band /overlap/.

The electrons in that overlap can move freely through the conductor.

So, they do not move from one band to another band, but stay
in the overlap region of two bands.

The part I'm unclear on: when exactly is it that the electron moves from
one part of the conductor to the next, i.e., down the wire?

The model is more of a statistical model. It does not specify
details about the exact time of the exact position of a single
electron.

Are we
just saying that, at the higher energy state, the electron will be
moving around the material more often?

Some electrons of low energy are in core bands where they are
tightly bound to their atom and cannot move away from it.

Electrons of higher energy are in the conduction band, where they
can move freely around the conductor.

Or that somehow moving from one
energy state to the other, is movement through the conductor?

In this model, electrons do not move from one band to another
band, which would mean they change their energy. Instead, some
electrons can be in the valence band and the conduction band
at the same time, because these bands overlap.


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From Newsgroup: sci.physics

Stefan Ram wrote:

In a conductor, the region of outermost electrons of one atom
/overlaps/ with the region of outermost electrons of neighboring
atoms, so the valence band and the conduction band /overlap/.

The electrons in that overlap can move freely through the conductor.

So, they do not move from one band to another band, but stay
in the overlap region of two bands.

Of two bands _of the same kind_ of _two neighboring_ atoms.

The part I'm unclear on: when exactly is it that the electron moves from
one part of the conductor to the next, i.e., down the wire?

The model is more of a statistical model. It does not specify
details about the exact time of the exact position of a single
electron.

However, an electron in the conduction band is not a free electron -- hence
the corresponding model is called *_nearly_ free electron model*; so it is
only more likely to move to a neighboring atom if there is an external
electric field as that exerts a force on the former and accelerates it; describing that with energies, because of that force it has an additional electrostatic potential energy that can be and is converted to (additional) kinetic energy.

Are we
just saying that, at the higher energy state, the electron will be
moving around the material more often?

Some electrons of low energy are in core bands where they are
tightly bound to their atom and cannot move away from it.

Electrons of higher energy are in the conduction band, where they

can move freely around the conductor.

Again, they are _only approximately_ "free". And they can only move around because not all energy states in the conduction band of _a neighboring_ atom are already "used" by an electron, IOW the conduction band of that atom is
not completely filled.

Or that somehow moving from one
energy state to the other, is movement through the conductor?

In this model, electrons do not move from one band to another
band, which would mean they change their energy.

This *also* happens, and whether and to what extent that is possible defines whether a solid acts as an electric conductor, an isolator, or a semiconductor.

Instead, some
electrons can be in the valence band and the conduction band
at the same time,

NOT *the same* electron, *ever*. A quantum object (like an electron) being
in two (different) states or two (different) places at the same time is NOT
a correct interpretation of quantum mechanics.

because these bands overlap.

Ridiculously wrong. This *never* happens. Instead, there usually is a
*band gap* between the valence band and the conduction band -- energies that
an electron _cannot_ have ("are forbidden") -- which is why and how we
identify these electronic energy bands in the first place.
--
PointedEars

Twitter: @PointedEars2
Please do not cc me. / Bitte keine Kopien per E-Mail.
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