What is The Radio Meter?
The radiometer or in other words the light-mill, was invented by the English Physicist Sir William Crookes. It consists of a set of vanes, when exposed to light, the vanes rotate.
As the vanes become warmer and repel air molecules from the surface the slight difference in air pressure created causes the vanes to rotate.
The speed of rotation is affected by the pressure within the vessel. Higher pressure will increase drag and will be the dominant force affecting the vanes while at low pressure the molecular recoil will dominate.Then there are the gas molecules, since, when the bulb is evacuated to a high vacuum, the vane will no longer rotate.
Some of the theories presented to explain what makes the Crookes radiometer go round. Photons notably of the infrared region of the spectrum absorbed by dark surfaces providing thermal energy that heats adjacent gas molecules. This pressurizes gas molecules at the surface, which shoves the vane in the opposite direction.Some of them have been satisfactorily disproved. If the pressure is reduced too far there will be too few recoiling molecules to drive the vanes.
The reason why I chose this project is because is interesting how a light bulb works without using batteries or electricity. The only energy that it needs to move is heat energy this is because light that bounces off the other surfaces imparts even more momentum, so the vane should be rotating in the opposite direction.