Date: Mon, 21 Oct 2002 18:08:29 -0400

Author: "Jason St. John"

Subject: Re: light the match demo

Post:

Mine are parabolic, too. I know that a parabolic reflector focuses
radiation from infinity at the focus, but if your source is closer than
infinity, the radiation will focus slightly nearer to the dish. In fact,
when I first found my set, I used the heat IR source near a single dish,
with the match a few feet away (the equal and opposite optical path).

So if your students know their geometry, you can do the demo at half the
cost.

____________________________________________________
Jason St. John 617.353.2634 stjohn@bu.edu
Boston University Physics Lecture Demonstrations

On 2002-10-21.12:56 owner-tap-l@listproc.appstate.edu sent:


I wonted to make another set a few year ago. I found some in Edmund
Industrial Optics item#53-875. I then had our shop make the stands. They
work well but I found that they have two focal points. It is possible that
our shop did something in the mounts that made this occur, Don't know.

Steve



At 12:25 PM 10/21/02 -0500, you wrote:
>I shared the handouts from this summers demonstration workshop with some
>other physics instructors and they immediately wanted to do several demos
>(two of which we already had) but we don't have the reflective mirrors to
>do PIRA 4B40.10 the light the match demo. Two curved mirrors (circular?
>parabolic?) one with a filament at its focus the other with a match. Turn
>on the current to the filament/reflector located on one side of the demo
>table and the match in the other reflector located at a distance is
>ignited. I recall that this one was discussed at the workshop but do not
>have any source for the reflectors. Does anyone have a source of some
>appropriate reflectors?
>
>Don Mathieson
>Tulsa Community College
>dmathies@tulsacc.edu

-TTFN :-)~

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