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qxs@rogers.com
science forum beginner

Joined: 25 Jun 2006
Posts: 2

Posted: Tue Jul 04, 2006 9:45 pm    Post subject: Radiation pressure -photon momentum

I've been 'reading' today.. and I'm at a confusion point.
When EM radiation strikes a surface it interacts with the
atoms(electrons) and stuff happens:
-reflections
-transmittance
-refraction
-absorption

it is dependant on the material.. metal.. glass.. whatever..

"Radiation pressure: When an electromagnetic wave (light wave) strikes
a charged particle, the light's electric field accelerates the charge
in a direction that is transverse to the light's propagation.
Acceleration of the charge creates a magnetic field that interacts with
the light's magnetic field and forces the particle forward in the
propagation direction."

Would this be for a metal?
What if the "charged particle" was a glass surface.. little or no
absorption/reflection/refraction, would there still be pressure on the
glass?
Is radiation pressure a property of absorption/reflection/refraction
only (ie if most of the light is transmitted then I guess it would be
silly to expect energy to be transferred as radiation pressure)?
In causing the radiation pressure the light loses it's energy
(absorbed?) ?

There is a crazy website where some guy in the 70s? was levitating
objects and fusing things together.. some relation to tesla coils.. but
it got me thinking..
Is it possible to have enough radiation pressure to levitate say 100kg?
I have seen the example of a laser levitating a tiny glass sphere.. but
what I'd like to know is if it is mechanically possible to create the
required amount of radiation in the proper wavelength to actually do
this for a large mass.. ie x-rayor gamma rays radiation?

----
Now, how is a photon's momentum related to radiation pressure?
ie if the light is absorbed, the object is 'moved' by radiation
pressure, then the photons energy must be gone.. wouldn't that be it's
momentum ?

I probably have some key points completely ass-backwards..but it's
hot.. and my eyes need a nap.

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