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Designed
& developed by great German Physicist, William Crooke,
Radiometer has since been named after him as Crooke's
Radiometer. Consisting of a set of vanes, each shiny on one side
and blackened on the other, these are mounted on a spindle,
balanced very senisitively, & set in an evacuated vessel. When
exposed to light, the vanes revolve. The blackened vane becomes
warmer than the shiny one repels air from the hot surface. The
slight difference in air pressure difference is what causes the
device to spin. Shows dramatically light does exert a pressure.
The rotation speed depends upon striking a balance between
molecular drag and recoil. At higher pressures, drag will
dominate and the vanes will fail to spin. At lower pressures,
there are too few recoiling molecules to drive the vanes. The
Radiometer is evacuated at optimum air pressure. Proves very
clearly the conversion of heat energy into mechanical energy.
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