Date: Wed, 27 Mar 2002 21:19:56 -0500

Author: Machele Cable

Subject: Re: hot filament lab

Post:

Geoff....several list members, including myself, have offered web space, free
of charge, for list posting. Some people really have a problem with
attachments (and I don't mean a personal problem, but a technical one). I'd be
happy to post anything you need to have posted in the future!

Chele

Geoff Nunes wrote:

> Jim McConville wrote:
> >
> > > > the filament and make a very nice lab demonstrating Stefan's law (power
> > radiated is proportional to T^4). Interested parties can contact me for
> > details.>
> >
> > I am an interested party. I would bet most other readers are I.P's. too.
> > Thanks.
> > Jim McConville,
> > Jackson County, Oregon
> > ojim@mac.com
>
> OK. First, I must apologize for the attachments, which I have tried to
> keep small. I have no place to post stuff.
>
> stefan.pdf is the write-up I used when teaching this lab to honors
> students. By the time they got to this lab they had had two previous
> intro lab courses with me in which I had been training them to think for
> themselves. So there is no procedure, only some leading suggestions.
>
> The required equipment is a power supply, two digital multimeters (a 4.5
> digit one for measuring the current is prefered), and a light bulb. I
> don't know the exact bulb, but I believe it was intended for a 6 V
> flashlight. They could be reliably run up to 6.5 volts, and
> occasionally beyond. VERY bright (hence the request for students to
> bring sunglasses to lab).
>
> They measure I vs. V, and convert to power vs. resistance. Using the
> resistance of the bulb at room temperature (here's where you need a
> sensitive current measurement because you don't want to warm the
> filament) they can convert their data from resistance to resistivity.
> Then they interpolate the given data to convert resistivity to
> temperature, to the final plot of power vs. temperature.
>
> There are three graphs (real data) attached. iv.pdf is a graph of the
> raw data.
>
> P_vs_T.pdf is a graph of power vs temperature with a non-linear fit to
> equation 4 in the write-up. It provides convincing evidence to the
> expert eye, but is a lousy way to teach about Stefan's law.
>
> The final graph linear_fit.pdf shows the data the way I try to have them
> analyze everything: If the hypothesis is correct, the data fall on a
> straight line. (For complete nut cases like me, there is even a way to
> do this with the Q curve for a lightly damped harmonic oscillator......)
>
> Modern physics labs are hard to come by, especially simple ones. This
> one fills the bill nicely.
>
> Have fun.
>
> -Geoff Nunes
>
> ------------------------------------------------------------------------
> Name: stefan.pdf
> stefan.pdf Type: Acrobat (application/pdf)
> Encoding: base64
>
> Name: iv.pdf
> iv.pdf Type: Acrobat (application/pdf)
> Encoding: base64
>
> Name: P_vs_T.pdf
> P_vs_T.pdf Type: Acrobat (application/pdf)
> Encoding: base64
>
> Name: linear_fit.pdf
> linear_fit.pdf Type: Acrobat (application/pdf)
> Encoding: base64

--
Machele Cable-----Lab Manager-----Wake Forest University

-----"Nothing shocks me. I'm a scientist." - Indiana Jones-----

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