Discoveries in the Physics & Astronomy shop | Science, curiosities, and surprises
When the screw heads to the battery access panel are stripped, just go all the way and open up the entire housing. Why not?
The real question is this: why are those screws stripped? Did it arrive that way, battery installed, or did they take a real beating after popping the first battery in? Why have screws to keep it shut in the first place?
In our Physics & Astronomy labs, we use metersticks with great frequency. Often for measurements, sometimes to approximate distances that make the arithmetic easier, and occasionally as a handy tool for pointing to the projector screen.
They aren’t super-high precision any more than the rulers you remember from elementary school, and for that we have other tools. Sometimes, as you can see above, the years have warped and twisted things a bit. We adjust.
As you might expect, they offer metric distances on one side, inches and feet on the other. The best ones – the oldest set – were long ago painted black to conceal those SAE units. Clearly, someone grew weary of students measuring everything in inches and then complaining that the math wasn’t working out right.
We’ve pointed out our old and reliable force tables before – classics of the undergraduate physics experience – which arrived here in several installments. Previously, 1957. This young’un only appeared in April of 1964, intended for the Physics 107-8 lab. Not listed in any recent course catalog, we’re uncertain of exactly what that was.
We could probably go pester some librarians, because surely there’s a record, but those folks are awfully busy on more important matters. Leave the idle wondering to the fellows here in the basement.
At any rate, they paid a healthy sum of $96.75 for this precision-machined beast. In today’s dollars: $985.65.
Do you think we’ve gotten our money’s worth yet?
For one lab, run once each academic year, we need about a half teaspoon’s worth of tiny polystyrene pellets, the kind that get pressed together to make the cheapest, crappiest, least environmentally friendly coffee cups around. Altogether, in a busy lab year, that’s still maybe a third of a cup. And we can recover some of them, because we filter everything before pouring the liquid down the drain.
And we’ve got enough of them sitting in storage to last a couple of lifetimes at this rate. Or to fill up a bean bag chair.
But do open with caution. Those little pellets want desperately to stick to everything, to get everywhere.
Sure, the other side says soft white, but let’s be honest: blanco suave sounds way, way better.
It can be a real pleasure to find old objects lying around, with their dates of acquisition marked on the side. January 29th, ’09!
Which ’09, exactly?
Olin Science Building was constructed in 1954, so it’s doubtful this particular post holder dates back to 1909. Especially as the lettering on both sides matches up.
So we were still purchasing equipment for the old, cast-iron optics rails as recently as 15 years ago? Wow.
Copper-coated steel BBs, used in several different labs throughout physics and astronomy. Like many of the odds and ends we use for labs and demonstrations, these aren’t used as intended by the manufacturer. In this case, one can only imagine that off-label use is actually safer.
Around here, we get great mileage out of springs, especially when studying waves and oscillations. And few helical coils grab attention quite like a neon-bright Slinky.
Honestly, if you had the choice between eye-searingly bright colors and boring old steel? We hope you’d go for bonus entertainment value, too.
Behold: a box which counts! That’s it, for the most part. It counts pulses of positive voltage. Very quickly, and you can set some thresholds to tell it to count certain values but not others.
It also gates over an interval you set, so you can tell how many pulses it receives over, say, one second. It counts, displays the total, then counts again. Displays the new number.
We use these for our wave/particle duality lab experiment, which relies on counting individual photons. Yes, those. The teeny, massless quantum packets of energy, the messenger particles of electromagnetism. Light. It acts in non-intuitive ways, and the students who think “that’s amazing and I want more!” sometimes become Physics majors.
Part of using this box – just one aspect – is helping convince those students that only one photon at a time can be reaching the photomultiplier tube sensor. At the speed they move, a mind-boggling number of photons can zip through that meter-long box without bunching up. c in air isn’t all that far from c in a vacuum, so if your one-second counts aren’t remotely near 299,792,458 (adjusted for PMT sensitivity and other losses), you know some of those photons are pretty lonesome. Sometimes you need a little math to make sense of things you can’t directly sense.
One other fun aspect is a little switch hidden on the back: cricket. It’s the volume switch, letting the box emit a little beep for every pulse it counts.
If you’re counting pulses from a radioactive source, which arrive randomly, it can be informative to hear these irregular signals, gated and grouped into numbers which show a decaying curve.
If you’re counting 100,000 photons every second, in a room of other lab benches also counting thousands of photons? Less informative, more irritating.
Sometimes, we have old equipment which is rarely, if ever used. Case in point: the mid-20th-century spectroscopes which have been supplanted by digital spectrometers. They’re both effective tools for examining a spectrum of light, one by eye and the other fed by a USB cable. Using a diffraction grating, they split light into its constituent spectrum – its rainbow, more or less – and can identify the presence of individual wavelengths. Not something our eyes can do, as they blend everything together, though that’s very helpful in most situations, such as reading this on your screen.
Summing bands of reddish, greenish, and bluish into a broad rainbow of colors is one neat-o trick.
With a diffraction grating, reflection grating, or prism, you can refract light out along a range of angles which correspond to its constituent wavelengths. Put a sensor at a known angle – your eye or a semiconductor exhibiting the photoelectric effect – and you know the wavelength if you sense a photon. It’s a simple piece of information which can be used to unlock a staggering amount of interesting, related information about what you’re observing.
You can also use a diffraction grating to get a quick sense of the entire visible spectrum of a source by holding it off to the side. Remember: the angle of the light’s path change as it refracts, so you’re trying to angle it back to your eye. Hydrogen has a distinctly pinkish-purplish hue when excited at high voltage, and you can see the dominant red and blue lines in its spectrum. With just that one electron to absorb energy and emit photons, the spectrum can only be so complicated.
That’s in contrast to helium, with its two electrons. The spectrum doesn’t look white, per se, but is much more filled out than hydrogen. Look at those spectral lines, and there are so many more! They’re distinct, measurable, and provide a “fingerprint” that can be immensely useful for scientific study. Or for just looking cool.