6 customer reviews
The vanes, or wings, in this solar radiometer are alternately dark and light in color. When the light strikes these wings it transfers heat to each one - but not at the same degree. The lighter wing reflects the rays and the darker wing absorbs. The stronger the light, the more energy there is to heat up the darker side of the wing causing the wings to spin faster. It spins under the solar light or a regular light bulb. Great for science projects, as a gift or as a desk amusement!
Uses heat transfer to spin
No batteries required; the radiometer is powered entirely by light
Either solar or indoor light works
Great desk toy
Great for solar science lessons
5.25 x 3.25 x 3.25 inches
13.34cm x 8.26cm x 8.26cm
0 lb 3 oz
directly observable interesting physics
Mark ODell from USA, CA, Los Angeles
Motion directly from light never gets old. This motion, however, is not due to photon momentum radiation pressure, or the direct pressure from gas warmed by the black faces. Such simple explanations turn out to be wrong. This is a light-driven heat engine. Even James Clerk Maxwell initially disagreed with Osborne Reynolds about the mechanism, so we are in good company watching and wondering. See Wikipedia Radiometer references for a lucid discussion, but know there is much more going on than the common explanations most of us learned when first seeing a Crookes Radiometer ("light-mill"). Cooling causes direction reversal. Improving the vacuum stops motion altogether. Radiation pressure is real, but the effect is too small here. The important mechanism has more in common with the flow of heat or superfluid helium than the momentum of photons or the pressure of bulk hot gas. The black sides do get hotter, but the ultimate magic of motion apparently happens at the edges of the vanes, not the faces.
Good Classroom Tool
Cynthia from USA, UT, Draper
This is an awesome way for students to learn that solar radiation is a form of energy.
Maria from Cedar Rapids, IA
Love to watch this work and think about the science behind it. Great tool for teaching about energy.
Great Conversation Piece!
Eric Holmes from Moose Jaw, Canada
Everyone that sees it will stop and look at it rotating and then will have a theory on what makes it rotate.
Joan from Tulsa, Oklahoma
This is so fun. I broke my mother's radiometer, so had to replace it. A good price for a great product.