Heebie Jeebies 22cm Crookes Radiometer

This is not a toy, but a magnificent teaching tool to illustrate electromagnetic radiation intensity. It's also perfect to spark conversations on how it works (or doesn't work) and why you'd have it displayed in your home or office (it's just cool!).

The Crookes radiometer (also known as a light mill) consists of an airtight glass bulb containing a partial vacuum, with a set of vanes which are mounted on a spindle inside. The vanes rotate when exposed to light, with faster rotation for more intense light. According to Arthur E. Woodruff, it doesn't work by radiation pressure (the vanes would turn in the other direction), or by an overall pressure increase of the gas, but by forces exerted by the residual gas along the sides of the vanes. Quite a fascinating topic.

(Reference: The Radiometer and How It Does Not Work; Woodruff, Arthur E. The Physics Teacher , Volume 6 (7) – Oct 1, 1968)

Please note:

The glass on a Crookes Radiometer is fragile. Suitable for ages 14 years+