Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

Re: radiometer paradox



Bob Sciamanda wrote:

Joseph Gress wrote:

I am puzzled by how a radiometer works. It makes sense to me that
. . .
Joseph Gress

Joseph,
You are speaking of the Crookes Radiometer. Conventional Wisdom treats
this as a thermal phenomenon. The container is NOT a high vacuum. The
blackened side of the vane absorbs better than the reflective side and
so attains a slightly higher temperature. The result is a higher air
(not radiation) pressure on the blakened side. I'm sure that Jearl
Walker's "Circus" book gives more details and references for this - I
don't have it handy. (In a high vaccuum, the radiation pressure would
dominate, and your expectation would be realized.)
--
Bob Sciamanda sciamanda@edinboro.edu

Addendum: If you refrigerate the Crookes radiometer sufficiently, the
thermal effect can be reduced so that the radiation pressure efect
dominates and the thing turns "backwards" (ie., in accordance with
Joseph's expectations) under a strong light.
--
Bob Sciamanda sciamanda@edinboro.edu
Dept of Physics sciamanda@worldnet.att.net
Edinboro Univ of PA http://www.edinboro.edu/~sciamanda/home.html
Edinboro, PA (814)838-7185