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Photon Momentum

What power (in Watts) must the beam of a 0.5 kg flashlight deliver if the recoil momentum of the outgoing photons is to suspend the flashlight against the earth's gravity? (Assume that all photons from the bulk are visible photons with wavelength tex2html_wrap_inline273 Å.)

A certain flashlight bulb consumes 10 Watts of electrical power. If the conversion efficiency from electrical power to light energy is tex2html_wrap_inline275 , what mass could the outgoing beam of light be able to suspend against the earth's gravity? By what percentage is this force, when averaged over a period of one second, expected to fluctuate?



Prof. Tomas Alberto Arias
Thu Feb 13 14:11:24 EST 1997