analysis instruments glass solar radiometer crookes radiometer RMS1838TA

About crookes radiometer :

The crookes radiometer is also known as the light mill an educational and physical demonstration object returned by the English physicist Sir William Crookes ( 1832–1919 ) in the year 1873 was invented.

This small physical and technical miracle shows you in a clear way how sunlight is converted to energy - the sun as an energy source of the future!
The crookes radiometer has become a technically interesting and entertaining object of modern living spaces and shows you at the window standing or hanging, every ray of sunshine through movement.

glass solar radiometer crookes radiometer RMS1838TA :

A Crookes' radiometer has four vanes suspended inside a glass bulb. Inside the bulb, there is a good vacuum. When you shine a light on the vanes in the crookes radiometer, they spin -- in bright sunlight, they can spin at several thousand rotations per minute!
The vacuum is important to the crookes radiometer's success. If there is no vacuum (that is, if the bulb is full of air), the vanes do not spin because there is too much drag. If there is a near-perfect vacuum, the vanes do not spin unless they are held in a frictionless way. If the vanes have a frictionless support and the vacuum is complete, then photons bouncing off the silver side of the vanes push the vanes, causing them to rotate. However, this force is exceedingly small.
If there is a good but incomplete vacuum, then a different effect called thermal transpiration occurs along the edges of the vanes, as described on this page. The effect looks as though the light is pushing against the black faces. The black side of the vane moves away from the light.