This is our most affordable Radiometer, great for students, classroom demonstration and as a fun & interesting scientific conversation piece. The Crooke's Radiometer was the first heat engine. Originally developed in the mid-nineteenth century by Sir William Crookes, he used the device to measure the intensity of sunlight. Crookes thought it was the 'pressure' of the sunlight that made the Radiometer work. Actually, it was the infrared energy in sunlight that made the vanes turn. Any source of infrared (heat) energy will power the Radiometer. Inside the Radiometer there are four vanes, each has one blackened side and one silvered side. It is encased in a clear glass bulb at very low air pressure, which allows the air molecules move about more easily. The different colors on either side of the "vane blades" create the convection currents and that causes the blades to spin when exposed to light or heat. The more intense the light is that shines on it, the faster the vanes inside will turn. With bright light shining on it, the vanes will turn at speeds up to 3,000 RPM! The Radiometer is a great tool in demonstrating the power of solar energy. A fun demonstration experiment for Teachers uses the "sun block" plastic window film you can buy at hardware or building supply stores. This film is designed to block the suns heat in the summer to keep your house cooler. Build 2 small cardboard "houses" with one having a clear plastic window and the other using the sun blocking window film in the window. When you place the radiometer in each one, you will see the difference in how fast the radiometer spins.
Crooke's Radiometer is about 5" high and 3" in diameter.
Looking for a more upscale/high quality Radiometer?
See our Precision Radiometer in our Radiometers section.
Crooke's Radiometer: $14.95