What's the diference betwee an photon and an electron?
http://www.quora.com/What-is-the-dif...nd-an-electron
... an electron is a tiny particle that has an electric charge, and
a photon is a tiny, massless particle that we can perceive as
light.

http://van.physics.illinois.edu/qa/listing.php?id=2348

Q: Why are photons (all wavelengths) considered to be
instruments of the so-called "electromagnetic force"? So far as I
know, please correct me, photons have no electrical charge nor are
they influenced by magnetic fields. The term "electromagnetic
spectrum" seems to me to be very inappropriate and highly
misleading.

A: Grahame- You're right that electromagnetic waves, whether
viewed classically or in terms of quantized photons, are not
affected by static electrical or magnetic fields. They have no
charge. Nevertheless, they do exert electrical and magnetic forces
on charged particles and magnetic particles. Viewed classically,
they consist of nothing but electrical and magnetic fields
propagating through space, so it's entirely appropriate to call
them electromagnetic waves. ...


Photons are little units of light -- they are the original "quanta" of
quantum mechanics. Their existence was hypothesized to explain the
details of the photoelectric effect -- photons with enough energy can
knock electrons out of materials. Since then, photons have been found
to play a central role in the explanations of many physical phenomena,
from explaining how much heat is radiated by hot objects to modern
quantum cryptography.

But on to your question! The classical model of electricity and
magnetism makes use of the ideas of electric and magnetic fields.
Maxwell's equations describe how these fields behave, and the Lorentz
force equation, which describes how the fields push and pull charged
particles and magnets. A prediction of Maxwell's equations is that
there are waves in the electromagnetic field which travel at the speed
of light. These waves were identified with light by the experiments of
Hertz and others. We therefore have two very different ideas for how
light works -- as waves in the electric and magnetic fields, and as
motion of particles -- photons. This pair of explanations is called
"wave-particle duality" and is a recurring theme of quantum mechanics.
Depending on the experimental situation, light acts as a wave or as a
particle (but never both simultaneously).

Weirder still -- static electric and magnetic fields also exhibit
wave-particle duality. The collision of a charged particle with
another (repulsive or attractive) can be modeled as the exchange of
photons and you get the same answer as if you had calculated
everything with just the classical fields (in the limit that the
classical calculation applies -- slow incoming particles). The quantum
calculation involving the exchange of photons is more accurate in
describing actual collisions at higher energies.

And now the really weird part. You might ask -- "Photons travel in
straight lines at the speed of light. Why doesn't the electric field
of a charged object just zoom away at the speed of light?" It turns
out that the photons which make up a static electric or magnetic field
are "virtual" -- their energy and momentum doesn't satisfy the
relationship for "real" photons -- E=p*c (E is energy, p=momentum, and
c is the speed of light). The virtual photons are constantly emitted
and reabsorbed. A charged object with an electric (and possibly also a
magnetic) field is surrounded by an entourage of photons, constantly
being emitted and reabsorbed.

Photons, real and virtual, are emitted and absorbed by charged
particles, even though they are not charged themselves. They only
interact with charged particles, and not with each other. That's why
photons don't interact with magnetic fields -- the photons which make
up the magnetic field are not charged so other photons cannot interact
with them.

Technical p.s.: photons have entourages of electrons (and other stuff)
around them, and so photons can interact with other photons by
interacting with this cloud of charged stuff. The effect is so small
it hasn't been observed yet for low-energy photons. Very high-energy
photons produced in particle accelerators may collide with themselves
readily.

Tom


Follow-Up #1: photon sources


Q:

....and how does a photon (real or virtual) carry or represent the
information about the charge (eg +/-) that it's interacting with?
- Paul (age 57)
UK


A:

It may be easiest to describe this in terms of classical
electromagnetic fields, which already contain the essential
ingredients. Charged particles are sources of these fields. The way in
which charged particles give rise to fields is captured in the Maxwell
equations. Charge itself gives rise to a 'divergence' in the electric
field. Current gives rise to a 'curl' in the magnetic field. However,
looking at the fields in some region does not give all the possible
information about the sources. For example, a static field might come
from a little nearby charge or a lot of far-away charge.
Mike W.

I conferred with our local guru on this matter, professor Michael
Stone. He thought about it for some while and then said 'It's
tricky'. His explanation is that an ordinary, free, photon has two
different transverse polarization states as can be easily demonstrated
by the usual crossed polarizers experiment. An electron that
interacts with this kind of photon couldn't care less where it came
from. It just scatters ala Compton. Now in the case of when the
photons are virtual, such as when two electrons are close to each
other and are experiencing
Coulomb-like forces, the photon has an extra, longitudinal,
polarization state. This extra state carries information as to the
charge sign of its source. Hence the electron receiving the photon can
decide whether to be attracted or repelled.

LeeH


http://physics.about.com/od/lightoptics/f/photon.htm
http://www.britannica.com/EBchecked/...83374/electron
http://hyperphysics.phy-astr.gsu.edu...iv/photel.html

:-)


On Tue, 15 Feb 2005 19:55:29 -0800, Roy Lewallen
wrote in :

One thing I didn't see explicitly stated in the answers is that the
progation of radio waves doesn't require electrons. It propagates just
fine in space, or even an empty vacuum. Radio waves are of course the
same sort of stuff (electromagnetic waves) as light, just a different
frequency. So if electrons were required for propagation, the light from
the Sun would never make it here.

Roy Lewallen, W7EL