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Re: [Phys-L] ?simple experiment limited by fluctuations





On 2018/Nov/20, at 20:59, John Denker via Phys-l <phys-l@mail.phys-l.org> wrote:


So the question is: Does anybody have a favorite *simple*
experiment where the uncertainty is limited by the physics
of the situation -- e.g. shot noise, thermal noise, quantum
noise, or some other property of the thing being measured --
not by technical limitations or roundoff error.

By simple I mean suitable for high-school physics course.



Many HSs I suspect have Vernier's “data loggers” or Pasco’s. The Vernier radiation monitor is $169

So simply recording the background (no need for a source) is what JD wants, and is simple. (I pray.)

I recently measured the dead time of a common G-M tube with the two source method over the rates (both ~ equal sources) ~ 20 => 2200 CPS.

The DT is extremely sensitive to the background at low rates and, of course, long counts (100’ +) required, as Poisson determined.

Result here: [poster at the recent NCNAAPT meeting in San Jose]


http://cleyet.org/Misc._Physics/radioactivity/DT%20(count%20rate).pdf


The lowest rate is, of course, suspect. For the lower rates (two or three), I recorded the background, for the same times I counted the sources, several times and then plugged into the formula the extrema background times. And used ~ the average; obviously suspect insufficient for the lowest one.

Somewhat later (now) I’m recording the background with the discontinued Vernier Monitor-4 and Lab Pro interface. The data points are hourly, so far > 400 hours. Tomorrow I’l stop and put the data in the file above. It has several outliers, which, I assume, aren’t. Maybe I’ll Chi Squared it w/ the assumption they are a Poisson distribution.


Again, I think this is an experiment available to all but the very poor high schools. One may query Vernier, as to how many HSs have purchased their data loggers. When I purchased the current one (Lab Quest two), I gave my Quest one to Chartwell school in Seaside.


shot noise,

I have (somewhere in our cavernous garage) an ancient (WW II) side window MPT (1P21?) packaged w/ a lamp. I’m rather certain it’s an anti-RADAR noise generator. Now this one is not so simple.

bc remembers the Brownian motion experiment he introduced back in 1984 using an HP spectrum analyzer $20k? very not so simple. My intro. of e-microscope polystyrene calibration spheres was essential. (I’d overhauled a(n) Hitachi TEM in my previous life. It was weird, the vacuum gauge was a discharge tube!)