Light pressure windmill

1. Content:

There are 6 glass covers on the booth, each with a cross inside. The cross can rotate around a vertical axis, and there is a black piece and a white piece at each end of the cross. Exhibition items showcase the absorption effect of different colored materials on light and the thermodynamic properties of gases.

2. Principle:

V light pressure

Light pressure refers to the pressure exerted on the surface of an object by light shining on it.

The thermal radiation of light demonstrates the conversion of light energy into mechanical energy. This exhibition consists of a rotating wheel and lighting fixtures sealed in a vacuum sealed glass container. If the glass container is completely evacuated, when the light shines on the wheel, the pressure on the blades with a black surface is half that of the white blades due to the light pressure effect (the momentum of photons reflected on the white surface is twice that absorbed by the black surface), which causes the blades to rotate from the white surface to the black surface. However, in reality, there is not a very high vacuum inside the glass container, and there is residual gas near the surface of the blade. The temperature of the gas on the black surface of the blade is higher than that on the white surface (because the black surface absorbs more heat than the white surface), which causes the pressure of the gas on the black surface to be higher than that on the white surface, thus pushing the blade to rotate from the black surface to the white surface. Due to the stronger effect of the latter, the overall effect shifts from the black side to the white side, where the blades continue to rotate under the illumination of light.

3. Purpose:

Exhibition items showcase the absorption effect of different colored materials on light and the thermodynamic properties of gases.