Painted Radiometer

42 €    [Ref. 7503]  Others currencies

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Glass blown and painted in Lauscha (Germany)
Diameter of the bulb: 8 cm
Glass stand

How does it work?

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 radiometer, they spin -- in bright sunlight, they can spin at several thousand rotations per minute!
The vacuum is important to the 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. The effect looks as though the light is pushing against the black faces. The black side of the vane moves away from the light.

Note: paintings are handmade and can be slightly different from the picture.

Different colors available: blue or pink
If you have a preference, please tell us in the order form ('Order preparation special requests'). Please note that we cannot guarantee your preference in the case a color is out of stock.

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