Re: Radiation Pressure of Light

On 2/9/2012 11:07 AM, WalterOrlov wrote:
On 9 Feb., 02:34, Jos Bergervoet<jos.bergerv...@xxxxxxxxx> wrote:

Quick summary: wave hits matter, charges feel E-field
and move proportional to E, Lorentz force is proportional
to movement times B, so proportional to wave amplitude
times wave amplitude, i.e. amplitude squared.

If you interpret it that way - ok. But in the first quarter period the
force e.g. positive and in the next quarter period - negative, because
the direction of motion of the electrons changes, but the direction of
the magnetic field still retains.

I think we agree. And it happens if the velocity is 90 degrees
out of phase with the B-field. Which happens if you assume
frictionless movement of one single moving charge. Corrections:

a) For a single charge, as I already mentioned, the friction
of the radiative self-force (Abraham-Lorentz force) removes the
exact 90 degree phase difference between v and E (and B).

b) For many-body situations: the field from all moving
neighbors adds to the incoming beam and there E and B are
not in phase (it's near-field zone!) This also cancels the
cancellation, even without using the A-L force (which is
not the dominant effect in that case anyway).

c) Friction from Ohmic resistance or other loss mechanisms.

NB: For a perfect conductor c) will not help! You need b).

--
Jos
.