Re: Electromagnetic wave and photon spin

rds wrote:
First off I want to say that I am not physics major.

Can someone explain to me the details of how electromagnetic radiation?

Your spelling is better than mine so you should find this
a breeze:
http://farside.ph.utexas.edu/teaching.html
http://web.mit.edu/8.02t/www/802TEAL3D/teal_tour.htm

Actually occurs. I know the pat answers that the acceleration of
charged particles or change in direction, but that doesn't really
explain the process.

Sun electron shakes, eye electron shakes 8 minutes later.
~~ R.P Feynman

For that matter why does a magnetic field form when current flows at a
constant rate (charge velocity)?


Magnetism is the geometric superposition of Coulomb
forces. The fundamentls are simple but the calculations
grow lots of hair because you can have to do them as
3 D volumes of space.
http://en.wikipedia.org/wiki/Multiple_integral

Where described as a moving charge
The electric field of the moving charges is interacting with other
matter which is ~stationary~ . At the minimum it is matter
in 'all of space' or 'free space'

permeability mu_0
permittivity eps_0
radiation resistance 377 ohms.


I notice in my car from 0 to 50 MPH , that when I accelerate I feel a
pull in the reverse direction, but when I reach the intended speed the
pull subsides. In some way this is counter intuitive in that I would
assume that the 50 MPH pull would continually cause a drag backwards.
In the same manner is this a parallel to the transmission of EM waves?
In that I get a transmission (radiation) when charges accelerate or
change direction?

Not quite. The ~pull~ an electron feels is relatvive to its Coulomb
coupling to nearby matter. A force about 10^32 time larger than
those you feel in your automobile.


Lastly the description of EM wave as abstract photons (all energy no
mass) makes sense to me in that the EM wave propagates as an E field
(sin) + an M field (cos). Is there an actual difference in the nature
of these two fields? Or are they indistinguishable from one another
--more like two E-Fields with a 90 degree phase shift

Yes... You are spot on. The E component diminishes by 1/r^2
and is the farfield or radiative component. The magnetic
component diminishes by 1/r^3 and is effective in the nearfield
only.

Photons are a mathmatical abstraction not a propagation model.
Your question is to the heart of why Feynman puts wrist watches
on his photons to fix all the mirrors that QM broke. In QED,
the phase information and magnetic components are transported
on the tip of a mathematicians pencil. ;-)



If the latter is true, and we take any point on the EM wave front an
examine it as it travels toward us, we could easily describe the EM
field as a mass less polarized point in space which rotates like a
plate
spinning with the top of the plate being positive and the bottom of the
plate
being negative. The spinning at the rate of the transmission frequency.
This totally describes the EM field without even referring to a
magnetic
field. As the plate rotates its positive to the 3 and 9 o'clock
positions it
represents the M field peaks, and at the 12 and 6 o'clock position it
represents the E field peaks. I would normally call this point a photon
and the rotation I would call spin. But I read that photon spin is
actually in the direction of travel, and so the spin must be something
different. Any comments clarrifications is welcome.

If photons were propgation models you've just made a fairly
good Feynman clock. But they are not. It really helps to have
a good grasp of Maxwell's equations before you assume too
much about photons. Then you can differentiate between what
nature is doing and what a maths operation is doing.

Time-independent Maxwell equations
Time-dependent Maxwell's equations
http://farside.ph.utexas.edu/teaching/em/lectures/lectures.html


Sue...


Thanks.....

.

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