Electron Band Structure in Germanium, My Ass (2001)(pages.cs.wisc.edu) |
Electron Band Structure in Germanium, My Ass (2001)(pages.cs.wisc.edu) |
Everything in the lab was broken, and the faculty knew it. They told us on syllabus day that about 50% of our lab time was going to be spent repairing the old shitty equipment. Why? Because unless you're working at MIT or CERN that's how labs in the real world work. Everything's broken and you don't have any funding but you still have to publish.
And truth be told I learned more about both basic circuits and how to foster a "get shit done" attitude from that class than any other lab class I had to take. The modules were on a rotation and I remember one of the groups that ended up on a particular experiment spent almost the entire semester fixing one module that nobody got to do that semester. It was an old out-of-production expansion card that plugged in to some old DOS box and interfaced with some piece of tech I can't remember. Literally everything about the setup was out of production. The amount of investigation and creativity they had to come up with in order to try and fix that experiment was impressive. I don't remember if they succeeded.
That lab was an experience.
The experiment, in brief, is to irradiate tiny oil drops and then tune a pair of charged plates until you can get one oil drop to levitate. Since electrons are unitary in charge, you can then back calculate the charge of the electron based on the charge you put on the plates.
The set up is that you have a microscope, an oil atomizer to make the drops, the charged plates, and a small radioactive source to put electrons on the oil drops. Spritz, open the lead chamber, irradiate, look at the drops in the microscope, tune the charge, repeat.
Numerous problems emerged:
Myself and my partner were pretty blind without our glasses, which you have to take off to use the microscope. So we could see nothing. (found this out on the first day, fuuuuun)
The oil drops, when imaged, are about the same size as your retina cells, in the given microscope. This means you can never be sure that you have an oil drop or your eyes are just too noisy to see it. (found this out by the end of the first week)
The room must be perfectly dark to see the oil drops in dim light, also you must take data on a computer or by writing somehow. (found this out on the first day too)
The small bit of radioactive material was made radioactive in 1961. Given the halflife of the sample, my banana was more radioactive (found this out in 2 weeks)
The plates weren't connected to anything. (2 weeks wasted)
The oil atomizer was meant for baby oil, not vegetable oil, as was given to us and wasn't actually atomizing anything. (another weeks wasted)
The end result was, well, nothing.
We got nothing. Not for lack of trying. I think I slept about 2 hours a night that whole quarter, the rest of the time was spent in the lab and on HW for other classes. My partner and I discovered that if you put your thumb over the co-ax of a high voltage, low current powersource it would zap you something fierce and keep you awake through the early morning hours. I also discovered that taking 2 ibuprofen per Rockstar will lessen the jitters of the caffeine enough so that you can read your own writing later on. So that's nice, I guess.
Stay in CS kids. Physics is for idiots.
Intuitively, this doesn't make sense to me. Microscopes have a focus. You should be able to adjust that focus such that the microscope is also correcting your vision, just like I (very nearsighted) have no trouble using binoculars without wearing my glasses.
What am I missing?
That's close, but not quite the real issue.
The lesson is to document everything. Repeatability IS an issue even if no one is going to repeat the experiment--because YOU need that information to make any progress. It allows you to isolate to one thing, change one thing, and see what the result is. And THAT is the core of debugging.
I wish I could send every programmer through a physics lab class. The number of times I have had the following conversation with software people is staggering:
"Well, I did X and it didn't work."
"Oh? So, what was it supposed to do before you did X and what was it supposed to do afterword?"
"I dunno."
"THEN WHY THE HELL DID YOU DO X AT ALL?" <bangs head on table>
Laser scientists know that if you use (a well anti-reflection coated) Ge window or lens to transmit a high power CO2 laser beam, slight absorption heats it a little. Heating it a little makes it more absorptive. So it heats a little more. And so forth, until the motherf——r cracks: “thermal runaway.”
Guess why? You are going to be a good experimental physicist eventually. Eventually. I spent two years blowing up homemade nitrogen lasers at Berkeley. Keep posting!
He switched to CS and now gets paid to work on A-list videogames all day: http://pages.cs.wisc.edu/~kovar/cv.html
Edit: Oops, LinkedIn says he's now at Google.
"Two years experience in swing dancing (east coast swing and lindy hop)."
I've found that to be very successful in all walks of life.
"Correct to within an order of magnitude."
Wrong.
Is it not possible to use four terminal sensing? https://en.wikipedia.org/wiki/Four-terminal_sensing Perhaps the sample is too irregular, but for very low resistance samples using only two terminals never work.
Can they use a lock-in amplifier? https://en.wikipedia.org/wiki/Lock-in_amplifier When it works, it's like magic. I'm not sure that it is useful here
> I attached them as appropriate to the second-rate equipment I scavenged from the back of the lab, none of which worked properly.
Yep, that's usual.
In next life, remember to be a mathematician.
Part of being a physicist is having a high pain tolerance to non-working hardware. This includes cables.
Edit: could be I'm thinking of Britney Spears' Guide to Semiconductor Physics, and I read this article later.
I think this got printed up and hung in the dorm common room as some cathartic exercise.
I dimly remember some other reports of a similar style on other subjects, but I don't recall what they were beyond that.
Citation: http://pages.cs.wisc.edu/~kovar/cv.html
We should have done a lot of things better, actually.
Maybe we really didn't have a microscope? The apparatus was built in ~1961 and had been used yearly for the next 50 years. Any semblance of a manual had long since disappeared. Perhaps a lens or two had been raided in the 1980's ans we couldn't figure that out in the soup of other problems. I've really no idea, a decade on, which of the problems we were having that was our 'show-stopper'.
All I know is that Advanced Physics Lab (2 units) continued the time honored tradition of the Physics major breaking you, and then kicking you while you were down and laughing at your idiocy, for 4 years straight.
Somehow, I miss those times...