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I would like to know if a radiometer will spin if exposed to laser light. Why? Why not?

I do not have the resources to test this out, but I cannot think of any reason why laser light would not cause a radiometer to spin. The black faces of the vanes will absorb laser light just like any other light, and become warmer than the bright faces. And it is that difference in temperature that makes the radiometer spin (please see answer to #628). Of course, if the laser beam is kept trained on just one of the vanes, it will probably take longer for rotation to begin than if, say, sunlight is used (I would be interested to know how long, if any, delay there is!)

Interesting question!


Of course, you also have to consider the total energy deposited on the radiometer vane. Remember that a laser has a high energy for a specific wavelength but NO energy anywhere else in the spectrum. Light from the sun has low energy at all wavelengths. The net result is you may be putting a lot more energy onto the radiaometer vanes with a 50 Watt light bulb than with a 100 mW He-Ne laser. A 50 Watt laser would work better than a 50 W bulb but would cost 10's of thousands of dollars.

gregory r bradburn

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