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Philip P | all galleries >> Galleries >> Science Entertainment > Crooke's radiometer
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21-Apr-2021

Crooke's radiometer

Panasonic LUMIX LX100 I
1/125s f/4.5 at 10.9mm iso200 hide exif
Full EXIF Info
Date/Time21-Apr-2021 07:10:33
MakePanasonic
ModelDMC-LX100
Flash UsedNo
Focal Length10.9 mm
Exposure Time1/125 sec
Aperturef/4.5
ISO Equivalent200
Exposure Bias0.00
White Balance0
Metering Modematrix (5)
JPEG Quality
Exposure Programprogram (2)
Focus Distance

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Dan Greenberg23-Apr-2021 22:46
How cool that you actually own one. ~V~ Thanks for the explanation of how it works.
joseantonio23-Apr-2021 03:38
so nice and creative.V.
Philip P23-Apr-2021 03:35
It was first made in 1873 so it should look like an antique.
Neil Marcus23-Apr-2021 03:15
It looks like a delicately made antique. Your explanation while eloquent makes my head spin. "V"
Philip P23-Apr-2021 02:21
Originally it was thought it was due to the momentum of photons, reflected off the silver surface resulting in an impulse of 2mv, and absorbed on the black surface resulting in an impulse of mv, so there was a net rotating force. This does occur, but produces insufficient torque at the light intensities used to overcome the friction. Furthermore, this explanation would cause it to rotate in the opposite direction to that observed. Studies showed the effect was maximum at a gas pressure of 7.5×10^−3 Torr, and it is caused by the black face of the paddles being heated to a greater degree than the polished silver faces. When air molecules hit the black faces they are bumped by the fast vibrating surface atoms, and bounce off with a greater velocity than the molecules colliding with the silver surface's slow vibrating surface atoms. Since every reaction has an equal and opposite reaction, a greater force is produced against the black surface than the silver surface. The reason there is a narrow gas pressure range, under which the effect is observed, is that the aerodynamic drag increases with pressure preventing perceived rotation at higher pressures, and the effect is completely lost under hard vacuum due to insufficient numbers of colliding air molecules.
David Buzzeo23-Apr-2021 01:34
That looks like a good place for it to sitting.I remember reading about them in university. But I still do not quite understand what causes the plates to spin. Well photographed. V
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