Maxwell versus Compton

kvblake

In classical EM theory if a plane EM wave moves in direction (+x) E,M
are perpendicular to x.
Let's have an electron in x1. The force would be eE and the electron
moves (becomes an impulse) preferably perpendicular to x. Preferably
because there is diffracted light which carries some impulse.
Nevertheless the main direction of the impulse must be perpendicular
to x (as I think).

But this is also the Compton effect. The electron is hit by a photon
(its direction and impulse must coincide with that of the classical
wave.) But then preferably the electron should move parallel to x
(with some angles spread around x due to the diffracted photons) -
look at this as statistical snooker.

Summary:
I. According classical Maxwell theory the electron moves preferably
perpendicular to x

II. According QM (Compton) the electron moves preferably parallel to
x.

What is wrong here?????

William R. Frensley

kvblake wrote:
> In classical EM theory if a plane EM wave moves in direction (+x) E,M
> are perpendicular to x.
> Let's have an electron in x1. The force would be eE and the electron
> moves (becomes an impulse) preferably perpendicular to x. Preferably
> because there is diffracted light which carries some impulse.
> Nevertheless the main direction of the impulse must be perpendicular
> to x (as I think).
>
> But this is also the Compton effect. The electron is hit by a photon
> (its direction and impulse must coincide with that of the classical
> wave.) But then preferably the electron should move parallel to x
> (with some angles spread around x due to the diffracted photons) -
> look at this as statistical snooker.
>
> Summary:
> I. According classical Maxwell theory the electron moves preferably
> perpendicular to x
>
> II. According QM (Compton) the electron moves preferably parallel to
> x.
>
> What is wrong here?????
>
The classical motion actually consists of oscillations perpendicular
to x with a superimposed acceleration parallel to x, when you take
both the electric field and the magneitc field into account. Read
Section 34-9 of Volume 2 of the Feynman Lectures on Physics.

- Bill Frensley

Igor

On Jun 5, 1:15 pm, kvblake <kvblake2...@yahoo.com> wrote:
> In classical EM theory if a plane EM wave moves in direction (+x) E,M
> are perpendicular to x.
> Let's have an electron in x1. The force would be eE and the electron
> moves (becomes an impulse) preferably perpendicular to x. Preferably
> because there is diffracted light which carries some impulse.
> Nevertheless the main direction of the impulse must be perpendicular
> to x (as I think).
>
> But this is also the Compton effect. The electron is hit by a photon
> (its direction and impulse must coincide with that of the classical
> wave.) But then preferably the electron should move parallel to x
> (with some angles spread around x due to the diffracted photons) -
> look at this as statistical snooker.
>
> Summary:
> I. According classical Maxwell theory the electron moves preferably
> perpendicular to x
>
> II. According QM (Compton) the electron moves preferably parallel to
> x.
>
> What is wrong here?????

Classical EM theory doesn't include the concept of photons.

William R. Frensley

William R. Frensley wrote:
> kvblake wrote:
>
>>In classical EM theory if a plane EM wave moves in direction (+x) E,M
>>are perpendicular to x.
>>Let's have an electron in x1. The force would be eE and the electron
>>moves (becomes an impulse) preferably perpendicular to x. Preferably
>>because there is diffracted light which carries some impulse.
>>Nevertheless the main direction of the impulse must be perpendicular
>>to x (as I think).
>>
>>But this is also the Compton effect. The electron is hit by a photon
>>(its direction and impulse must coincide with that of the classical
>>wave.) But then preferably the electron should move parallel to x
>>(with some angles spread around x due to the diffracted photons) -
>>look at this as statistical snooker.
>>
>>Summary:
>>I. According classical Maxwell theory the electron moves preferably
>>perpendicular to x
>>
>>II. According QM (Compton) the electron moves preferably parallel to
>>x.
>>
>>What is wrong here?????
>>
>
> The classical motion actually consists of oscillations perpendicular
> to x with a superimposed acceleration parallel to x, when you take
> both the electric field and the magneitc field into account. Read
> Section 34-9 of Volume 2 of the Feynman Lectures on Physics.
>
> - Bill Frensley
>
It is actually in Volume 1. My copies are so worn it is hard to
read the covers.

Daryl McCullough

In article <1181028633.767979.151210@g4g2000hsf.googlegroups.com>, kvblake
says...
>
>In classical EM theory if a plane EM wave moves in direction (+x) E,M
>are perpendicular to x.
>Let's have an electron in x1. The force would be eE and the electron
>moves (becomes an impulse) preferably perpendicular to x. Preferably
>because there is diffracted light which carries some impulse.
>Nevertheless the main direction of the impulse must be perpendicular
>to x (as I think).

No, that's not actually correct. A travelling EM wave
*oscillates*, which means that the electric field points
in one direction at one moment and in the opposite direction
at a later time. The net effect on a charged particle is
*no* change in the velocity of a charged particle perpendicular
to the direction of propagation.

But what about the velocity parallel to the direction
that the EM wave is travelling?

Think about it: Suppose that initially the electric field
is pointing in the y-direction, and the magnetic field is
initially pointing in the z-direction. The electron is
initially at rest, but starts to move in the -y direction
due to the electric field (because it's negatively charged).
But a moving electron is also
subject to a magnetic force, which is perpendicular to
both the direction of motion of the electron (-y direction)
and the direction of the magnetic field (+z direction).
So the electron will develop a small velocity in the +x
direction.

Later, the electric field rotates slightly so that it is
now pointing with a small component in the +z direction. The
magnetic field rotates so that it is not pointing with
a small component in the -y direction. The effect of the
electric field gives the electron a small velocity component
in the -z direction, and the effect of the magnetic field
again gives it a tiny impulse in the +x direction.

When the electric and magnetic fields have completely
rotated around, then the electron will have no motion
perpendicular to the x-direction, but will still have
a slight velocity in the x-direction.

--
Daryl McCullough
Ithaca, NY

BorisDCLCXVI@gmail.com

On 5 juin, 19:15, kvblake <kvblake2...@yahoo.com> wrote:

> In classical EM theory if a plane EM wave moves in direction (+x) E,M
> are perpendicular to x.
> Let's have an electron in x1. The force would be eE and the electron
> moves (becomes an impulse) preferably perpendicular to x. Preferably
> because there is diffracted light which carries some impulse.
> Nevertheless the main direction of the impulse must be perpendicular
> to x (as I think).
>
> But this is also the Compton effect. The electron is hit by a photon
> (its direction and impulse must coincide with that of the classical
> wave.) But then preferably the electron should move parallel to x
> (with some angles spread around x due to the diffracted photons) -
> look at this as statistical snooker.
>
> Summary:
> I. According classical Maxwell theory the electron moves preferably
> perpendicular to x
>
> II. According QM (Compton) the electron moves preferably parallel to
> x.
>
> What is wrong here?????

You forgot the magnetic field. It is actually the radiation pressure,
a
classical effect occuring for every wave. The oscillatory motion of
the
electron then emits another, non plane, EM wave, with a wavelength
depending on the direction because of the Doppler effect. In contrast
to what is generally thought, the Compton effect thus isn't an
evidence
of the existence of the photon. Anyway, even with photons it isn't a
scattering, but the photon is absorpted and reemited.