#light mill

[consolecadet]

[logikblok-blog]

A Crookes Radiometer.

This device is also known as a light mill. It’s shaped like a bulb with a set of four vanes one side of each is black and the other silvery white. When exposed to the light the vanes rotate and on bright sunny days like the one above they rotate even faster. 

The explanation for this movement took a while to agree upon. Explanations ranged from light pressure to imbalances in heat.

The agreed reason for its movement is due to a pressure difference of hot and cool air molecules inside the bulbs vacuum. The effect is known as thermal transpiration discovered by Osborne Reynolds.  As the sunlight heats gas molecules inside the Radiometer they move from the cold side toward the hot side across the edges of the vanes, this pressure difference causes the vane to move.

#logikblok