A bag full of goodies for each and every student studying classical and modern physics this upcoming semester. Yo-yo, fidget spinner, bouncy balls (large and small), rubber ball on string, silicone fun poppers (large and small), metal coil spring (not a Slinky, but really it’s a Slinky), and a pair of balloons. Drinking birds and blowguns (not pictured) to be distributed later in the semester.
For those wondering: the big bouncy ball is way better than the little one. Same goes for the fun poppers. The little ones hop a bit, while the big ones bounce all over the shop. You know, for science.
Dice! Bins of colorful dice, each with 178 of one bold color, plus two going their own way. Each bin arrayed in a 10 x 18 or 12 x 15 grid, per the shop tech’s preference at that moment. Beats counting them one by one.
Secure the lid and shake with all your might: you’re simulating radioactive decay! Loudly.
Pick a number from one to six. Say, three. Each die that turns up with three pips after a shake decays, and you remove it from the bin. With 180 dice in there, the chances of getting all threes – or zero threes – is vanishingly small. One-in-six raised to the 180th power, right? As a percentage that’s, what, nearly 140 zeros after the decimal point? Run the numbers, and you can look forward to around one-sixth of the dice in there decaying with each shake. Sometimes more, sometimes less.
You’ll also keep a close eye on those differently-colored dice. One for you, one for your partner. They’re the atoms you’re watching carefully, and unlike the sorta-predictable rolls of a large mass of dice, they’ll decay when they’re good and ready. Could be first, could be never. It’s an illustration of how probability works in systems of different sizes. Of how the random nature of radioactive decay produces a predictability with enough atoms and enough time.
In some idealized version of this experiment, you’d have 30 dice decay on the first shake. Then 25. Then 21. 17. 15. 12. 10. 8. 7. 6. 5. 4. 3. 3. 2. 2. 2. 1. 1. 1. After that… maybe one per shake? (The student experiment stops well before you’re down to a meager handful of dice.) The half-life arrives around four shakes. Every four shakes. Neat!
And should the effect with 180 dice not be enough? Compare your data to the rest of the lab, seeing how each rate of decay is nearly but not exactly the same. Then aggregate the data from all dozen lab benches. 2,160 dice decaying.
What’s your favorite holiday? Whichever you choose, it’s kind of like that around here, because it’s almost toy kit time! Classical and Modern Physics I – better known ’round here as PHYS 211, or just plain old 211 – gives out a bag full of toys to each and every student. More than three hundred of these are getting ready for distribution.
We do the same for PHYS 212 in the spring, with all sorts of goodies for electricity and magnetism, but in the fall, it’s all about mechanics. Stuff that moves. Toys, exactly like you’d expect them to be. Yo-yos, Slinkys, bouncy balls, blowdart guns, drinking birds, and more.
Always balloons. Every toy kit, every semester, we include balloons. For science. More specifically to help illustrate the principles of physics for homework and problem-solving sessions. What better way to learn than with hands-on experimentation?
Here we have that childhood classic, the Duncan Imperial. Some of the kits will get the Butterfly instead – when you go purchasing hundreds at a time, you take what’s available and fits in the budget – but either way, it’s the return to a certain moment of childhood. At least for the shop techs. If there’s anyone in this world who’s guaranteed to get excited about nifty gizmos, it’s us.
(If there’s anyone in this world who can have serious conversations about the varying quality and potential factors affecting a bouncy ball’s bounce, it’s us. But that’s a topic for another time.)
And, since you were bound to ask: no, neither of us can remember how to do any of our childhood yo-yo tricks. Doesn’t stop us from trying.
Radioactivity makes people squirm. It’s not hard to understand why. Whereas most potential dangers offer some sensory warning, radioactive materials don’t. For the most part. If your senses are picking up the direct effects of radiation, you are long past any level of safe exposure. Somehow, things have gone quite sideways for you.
But this is introductory Physics lab, and we’re here to learn in a safe environment. We’ll stick to sources that keep below the United States Nuclear Regulatory Commission’s Exempt Quantity Limit. That’s readily available in the table from § 30.71 Schedule B, which indicates the limits in microcuries [µCi] for a wide range of nuclides. In our labs, we use cobalt-60 and cesium-137 for different purposes, though you can have fun reading through the entire table to remind yourself that dysprosium, hafnium, and samarium are all on that periodic table, too.
Lots of elements struggle to become household names. Maybe it’s for the best that most of don’t have to concern ourselves with the particulars of terbium on a daily basis. (It’s key to creating the green phosphors essential to fluorescent light, so now we’ve all learned a new factoid.)
We use these little 1-inch disks as relatively constant reference sources in labs. The disk, of course, is way bigger than the tiny chip of cobalt inside, which randomly decays into a stable isotope of nickel-60, spitting out a beta particle (an electron) and some gamma rays (high-energy photons). While it’s impossible to predict when any specific atom will decay, a sufficient quantity of them all bunched up together result in an output that’s mostly predictable. In any given second, you might hear several (or zero) clicks on your Geiger-Müller counter, but if you count them over longer intervals, the clicks-per-interval numbers get awfully close to each other.
With a half-life of 5.27 years, one little disk of cobalt-60 can handle years of students labs. While we wait for Physics 212 to roll around again, they bide their time in this little box:
Big sticker!
We keep it way in the back of a locked storage room. It’s lined with lead on the inside, even if that’s not strictly necessary. You probably shouldn’t stuff a bunch of cobalt disks in your pocket for the day, and you definitely shouldn’t eat any. (Physics labs don’t typically use edible materials, and even when we do – such as non-dairy coffee creamer – we mark them as not for consumption. Just don’t eat anything in the lab, okay?) It does keep everything in one easy-to-find place, though, and big CAUTION stickers tend to keep curious fingers out.
We use big, scary yellow CAUTION signs in the shop to keep curious fingers away from sharp objects, too. Sharp and poky things are way more likely to ruin your day around here. So be careful, please.
When a faculty member retires, they tend to leave a variety of things behind in their labs. With the busiest days of physics research behind them, and only so much spare garage and attic space, old pieces of scientific apparatus don’t make the cut. That doesn’t mean they’re not useful to someone else. Sometimes old equipment, built for a long service lifetime, still works pretty well. Those few things built without integrated circuit boards and lacking in bells and whistles? They’re tanks. We collect those, make sure they’re in good working order, and keep them handy for the next person who needs them.
Take, for example, the good, old-fashioned variable autotransformer, often called a Variac in the same way you might refer to any office copier as a Xerox machine. There are easily half a dozen floating around here. Probably more if you take time to look in the dusty corners. The short version is this: you send in ordinary AC line voltage, turn the big, chunky dial, and it sends out a lower AC voltage based on that setting. It has two moving parts: a sliding brush that moves along the wiring coils, and a switch.
Always love a reliable mechanical switch. Click!
An autotransformer has only one winding inside it, and outputs one or more voltages different from its input depending on where they tap into the coils. (A standard transformer has two windings. There are pros and cons to each.) A variable autotransformer has a sliding/rotating connection on the secondary side, enabling smooth voltage change from more or less zero to full. The number of coils the current passes through on its way to the brush’s connection determines the output voltage.
It takes advantage of the constantly-changing nature of alternating current. The flow of current creates a magnetic field; a changing current creates a changing magnetic field. A changing magnetic field creates a current in a circuit. Plugging a variac into the wall receptacle works. Connecting up a DC battery won’t.
They’re handy for testing electrical equipment, including motors whose speed is voltage-dependent. We use them in undergraduate labs in connection with incandescent lamps to study blackbody radiation; they’re a big dimmer switch that’s easy to control and understand. The core of a Mel-Temp apparatus, that workhorse staple of a chemistry lab setup, is just a Variac connected to a big resistor. The varying voltage adjusts the current, which controls the amount of heat it gives off to melt your sample.
Some of the old styles are Art Deco-ish beauties, too, with amazing names. Adjust-A-Volt! Powerstat! Every space-age laboratory deserves a few of these.
There are a wealth of options when choosing a telescope. Refractor (lens), reflector (mirror), or catadioptric (both)? How large an aperture (because letting in more light lets you see fainter, more distant objects)? Manual or computerized control? Optical viewing, astrophotography, or both? Alt-azimuth or equatorial mount? And so on. Dedicated astronomers can get deep in the weeds on the finer details.
What they all have in common is a BIG WARNING often in BRIGHT RED ALL CAPS that you should never, ever, point your telescope at the Sun. It’s solid advice.
Looking directly at the sun with your naked eye is likely to cause permanent eye damage. Doing so with the extra light-gathering power of a “light bucket” only accelerates the problem. Even if you don’t peer through it, the heat that builds up within the telescope’s delicate optics is enough to irreparably damage them and ruin your very expensive equipment. What’s an aspiring solar astronomer to do?
Find a solar telescope, of course. A few special features make this telescope safe for solar viewing (and somewhat less useful for anything else). It has a very small aperture, because it really isn’t necessary to collect more light from the brightest thing in the sky. It has a small section of opaque glass on top of the telescope which shows a pinpoint of light when the sun is approximately in view. And, best of all, it has an narrowband filter around H-alpha.
H-alpha is a specific wavelength of light emitted by excited hydrogen atoms, about 656nm, and the brightest hydrogen emission in the visible wavelengths of light. It’s quite red. It’s also, through a suitably narrow filter, something you can safely observe with your eyes. Pare away the other visible light, all of the UV and IR, and you’re left with the sun. Red, intense, and through the proper set of optics, magnified so that you can see amazing things.
Prominences erupting from the surface. Dark filaments that indicate region of magnetic shear. Sunspots and flares. The speckled, roiling surface of a star that’s like an orb of churning lava. It’s very cool. Astronomy you can study without staying up all night.
Greetings from one of the unofficial mascots of Physics, the drinking bird! Forever wearing its top hat, this classic toy is found all around the department. Though we keep a drawer full of them in storage, there are a handful about the shop shelves, professors’ offices, and occasionally elsewhere. The drinking bird is an example of a heat engine, which converts heat into mechanical energy.
Drinking birds are especially fun because they operate at room temperature. Two glass bulbs are connected by a tube and filled with methylene chloride, which has a low boiling point and condenses and vaporizes readily within the vessel. When the upright bird’s felt-covered head is wet, evaporative cooling causes a vapor pressure differential between the two ends. As liquid from the bottom rises, the bird becomes top-heavy and leans down for a drink, re-wetting the felt and priming the process to repeat. It’s an entertaining demonstration of the effects of various laws of physics.
There’s the ideal gas law, of course. Temperature change causes pressure change, which causes a shift in the balance of liquid and vapor. That shift in mass results in a center of mass that oscillates from one side to the other of the fulcrum, creating torque and movement. For as long as the bird can re-wet itself and maintain the temperature differential, the heat engine will continue to operate.
Alternately, you can apply a heat source to the lower bulb to get the same effect, which is the basis for most heat engines. There are many options to produce heat, and a wealth of engine designs to turn that thermal energy into useful work. But few are as simple, visually apparent, and entertaining as a bobbing glass toy.
