# Question about electricity and atoms, electrons.

Discussion in 'Electronic Basics' started by Ole, May 16, 2004.

1. ### OleGuest

When there goes a electric current trough a wire, is it just the
electrons that moves / jumps from atom to atom and the atom is not
moving or does the atoms also move?

How does the electro magnetic fields work, when you transmit a signal
from a antenna, the atoms and electrons doesn't move, the electrons on
the atoms just rotate the same way as the atom it's get affected by -
is this right?

Regards
Ole

2. ### John PopelishGuest

In metals, only the electrons move, and only a small fraction of them,
at that. The atoms are held in rigid positions (with only a little
thermal jiggle allowed) by electrons that each atom shares with its
nearest neighbors. But in metallic elements (and mixtures of metallic
elements) there are one or at most two electrons from each atom that
are shared over a larger volume than just the nearest neighboring
atoms. These conduction electrons amount to a gas in which individual
electrons can wonder at random, throughout the metal. This gas also
drifts if a tiny electric field is present in the metal. That slow
drift is ordinary electric current. The electron wind blows quite
slowly during ordinary current densities, but the electric field that
motivates to propagates through metals at nearly the speed of light.

In semiconductors there are positive equivalents of electrons that are
nothing more than the absence of conduction electrons (balanced by an
absence of protons in the atomic nuclei) that have properties very
similar to conduction electrons (they can hop from atom to atom),
except that they have a positive charge instead of a negative one.
They are commonly referred to as holes. In solutions, gases and
plasmas atoms missing one or more electrons are called ions and since
they are free to move, they can contribute to current (movement of net
charge) in addition to free electrons. In high energy physics there
are also rare particles like anti electrons and a whole zoo of other
particles that have electric charge and can take part in current.
Wish I knew, exactly. The idea is that anytime an electric field
changes strength, it generates a magnetic field (at right angles to
it, no less). And any time a magnetic field changes strength, it
generates an electric field (at right angles to it, also). So even in
completely empty space, electric and magnetic fields make each other
in a repeating process that propagates as a sort of wave at the speed
of light that replicates the frequency that launched it.
Do a search for Maxwell's equations is you are interested in how
compactly this process (and all the other linear properties of
electromagnetism) can be described.

When such a wave reaches a conductor, some of the energy in these
fields generate voltage (electric fields over some distance) and
current (charges that move in response to electric field) in that
conductor, also. And If the conductor is appropriately sized and
shaped to cooperate with these waves, a usable signal can be extracted
from the conductor as the waves passes. This works in reverse, also.
If a signal is applied to the same shaped conductor so that it carries
current at the wave frequency, it will launch electromagnetic waves
into space. Keep in mind that everything I have told you is wrong at
some level of accuracy. The only way to precisely describe what is
known about what is going on is with mathematics.

3. ### Bill VajkGuest

Nicely done, as usual, however I'll add this tidbit. You
can correctly think of the "electro magnetic field"
transmission you're describing (radio waves) in
exactly the same context as visible light but at a
different frequency. What you sorta kinda do is
"boil off" energy from a radiating element of some
sort which has a way of moving through space or many
real mediums, like air, till it hits something that
detects its presence as an effect.

There is an entire huge spectrum of electro magnetic
waves which include things like light and x-rays in
addition to the radio frequencies most people
associate with electro magnetic waves. Try
the links:

http://www.phy6.org/stargaze/Sun5wave.htm
http://www.colorado.edu/physics/2000/waves_particles/

4. ### jwGuest

Check out the book "Electomagnetics Explained" by Ron Schmitt.

--jw

5. ### Kevin AylwardGuest

In my view, the easiest way to get to grips with some basics of EM is by
the basic overview of the complicated account, that we usually only
learn about much, much later. That is, quantum electrodynamics, or QED.

QED explains *all* of electromagnetic phenomena by the momentum exchange
of photons between charges. That is, *all* electro-magnetic fields are
essentially, nothing more that billions of photons moving about in
strange (statistical) ways. It is not the direct motion of electrons (or
ions) moving that actually constitutes the "real" electric current, they
usually move very, very slowly, where as electromagnetic effects travel
at the speed of light. The falling domino effect is the better way to
view what "current" is. That is, as soon as electron moves, its photon
exchange with its nearest electrons is felt essentially, instantaneously
(speed c), and this is propagated along to next ones. The idea of
momomentum exchange as the EM force can be illustrated by two skaters on
ice throwing balls at each other. Each throw causes the thrower to move
backwards. The harder bit is accounting for an attractive force, but
this is all in the (complicated) wash in QED.

Kevin Aylward

http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.

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