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[Phys-l] radiation pressure



I found the following paper to be a bit startling. Did anyone else notice it:

Rothman & Boughn "The Lorentz force and the radiation pressure of light," AJP vol. 77, p. 122 (Feb 2009)

The gist of it is they claim the familiar derivation of radiation pressure in intro texts is wrong.

To remind you of this derivation, it goes as follows: An EM plane wave is normally incident on a conductor, say E in the x direction, B in the y direction, propagation in the z direction. Consider a free electron on its surface, initially at rest. The E field pushes the electron in the -x direction so it acquires velocity v in that direction. Then -e(v x B) is in the +z direction, giving radiation pressure.

The authors go through this derivation more carefully than intro texts and show it doesn't work if you're less cavalier.

Next comes a section called "Interpretation" which I can't fully follow, but the upshot of which is that radiation reaction is a necessary part of the real story. Skipping over that, they nevertheless then give an alternative "elementary" approach involving the boundary conditions for E and B at the surface and indicating that an induced surface current is involved (although there is a subsequent remark about "no Munchausen effect" that seems to weaken their development in my mind).

Anyhow, the bottom line is: They've convinced me that the traditional "derivation" is bogus; they've confused me about what the real story is; and they've given me an alternative approach that I wish could be further simplified if I'm going to use it in an intro course.

I'd be mighty interested in what the rest of you think about all this. -Carl