letters to the editor
rotate is due to thermal and not optical effects. However,
many schools may not have tube heaters on hand. One can
instead use a hair dryer (or heat gun). One can then show
the blades vigorously rotate even if the hair dryer is aimed
straight down on the radiometer bulb from above, perpendicular to the blades. That makes it clear that the rotation is not
due to radiation pressure from infrared photons issuing from
the incandescent bulb or thermal heater in Fig. 1 of Ref. 1.
1.
V. I. Hladkouski and A. I. Pinchuk, “A new way to demonstrate
the radiometer as a heat engine,” Phys. Teach. 53, 109–110 (Feb.
2015).
Carl Mungan
Physics Department
U.S. Naval Academy
Annapolis MD 21402
mungan@usna.edu
Activating a radiometer with a hair dryer
An article in the February issue uses a partly closed tube
heater placed around a radiometer to cause the blades to rotate.1 This demonstration indicates that the reason the blades
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