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Re: Radiation Pressure



John DaCorte asked:

What causes radiation pressure?

This question gets right to the heart of one of introductory students'
favorite questions, "If light doesn't have mass, how can it have
momentum?" Well, the story goes, light is composed of time varying
electric and magnetic fields. Fields describe forces on charges.
Forces cause charges to accelerate. So, charges which did not have
momentum before interaction with light may have momentum after the
interaction. Ergo, if momentum is conserved, the light must have had
momentum to start with.

I remember, in the distant past, an elegant Maxwell's equation
calculation of the interaction of an EM wave with charges which
confirmed the appropriate relationships for momentum of light.

Would appreciate comments illuminating this elementary explanation.

Cheers,

Rick

--
Richard E. Swanson, Ph.D. (910) 695-3715
Professor of Physics FAX: (910) 695-1823
Associate Dean for Development and Technology
swansonr@sandpiper.sandhills.cc.nc.us
Sandhills Community College
Pinehurst, North Carolina 28374 "He who laughs, lasts."