🚀 go-pugleaf

Hi,

I teach 9th grade science and I would like a definitive word on how a
radiometer works. They are the "toys" that consist of a clear glass bulb
with freely rotating vanes inside. The vanes are painted white on one
side, black on the other. The vanes will spin in the presence of bright
light.

I believe that momentum conservation requires the photons to be imparting
their momentum to the vanes. Since photons have no rest mass, the mass
they contribute to momentum is relativistic, m = E/c^2. Since they are
traveling at speed c, the momentum becomes E/c. Is this view correct?

Another teacher I work with thinks it has something to do with convection
currents set up inside the bulb. Yet I always assumed the buld was
evacuated  (a vacuum).

Thanks for helping out!!

                                    "Is this a train robbery"?    
Thanks! Sincerely,                  "No...it's a science experiment".
Kevin Luttrell                               - Back 2 the Future, III