Date: Tue Feb 6 14:57:42 2007

Author: Bernard Cleyet

Subject: Re: Evacuated Radiometer?

Post:
Well, not exactly -- the explanation is very complex. The last word
was given in a colloquium a few years ago at UCSC, being, I think an
updated version given by Wiki.


http://en.wikipedia.org/wiki/Crookes_radiometer

The above is also a source of additional demonstrations, e.g. cooling
the glass envelope, etc.

bc, uses one to decide whether to lower the blinds to conserve heat.


Gary Karshner wrote:

> Matt,
> Your standard radiometer is evacuated, but the effect you see
> is because of the difference in temperature between the sides. The
> residual gas when it collides with the hot side leaves with more
> momentum then the cool side, and the vanes reaction to those
> collisions is what drives it around backward. Black side following. I
> am told if you continue to evacuate the bulb (very high vacuum) the
> rotor stops because friction is too great.
> We had a student a number of years ago that tried to drive the
> vanes with a 35 watt laser with mixed results.
>
> Gary
>
> At 11:55 AM 2/6/2007 -0600, you wrote:
>
>> Howdy all,
>>
>> My oh my, the conversations have (pardon the pun) heated up lately on
>> the list :)
>>
>> Seriously though, speaking of thermal physics, I'm in the market for
>> an
>> evacuated radiometer. I want to show my students the difference
>> between
>> one full of air and one with a vacuum inside. From what I understand,
>> they will rotate in opposite directions.
>>
>> I have a standard air-filled one, but I don't know where to get my
>> hands on an evacuated one. Any ideas?
>>
>> Cheers,
>>
>> Matt Lowry
>> Lake Forest High School
>> College of Lake County
>> Illinois
>
>
>
>

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