Home-made circuits

Turns out, you can make conducting play-dough.

Notation

So we've discussed the fact that physics notation has quite a bit of historical baggage, and lacks precision at times (same symbol, different quantity ...).

Counterpoint.

This is a problem in teaching physics

Precision in language is important, but it is a slippery slope.

Another day in the kingdom of fear

I'm glad we're still letting you do real, live labs with real, live equipment. Unlike these geology students, who can't have real rocks ...

(Or, heaven forbid, you try to find a chemistry set anymore. Sigh.)

So, even if you don't particularly like the labs, you can consider it something of a privilege to be allowed to do them anymore ;-)

Punting

Let's punt Friday's quiz in celebration of your dominance of my first exam.

You win this round. [shakes fist]

There is, however, still a homework coming out shortly that is due Friday.

Things which tempt me greatly

This.

As the undergrad adviser for physics and astronomy, I enjoy giving undergraduates advice. Occasionally, however, when confronted with a vague question, it is hard to resist the temptation to be a bit silly ...

With regards to the link above, I'm thinking of some sort of Fight Club crossover, "My class is Jack's inflamed appendix."

In other news ...

Remember what I said about photons having momentum, and how one could use that for spacecraft propulsion?

Done. Very cool stuff, though the linked summaries are somewhat ... lacking. Knowing what you know of relativity and mechanics, can you spot some places where the articles are incorrect or misleading?

Wedensday's lab

Wednesday's lab will be all about capacitors, or at least how they combine in parallel and series.

You can find the procedure here.

Apologies for posting it a bit late, but please read the whole procedure before getting started with anything and start connecting wires, capacitors, and power supplies all willy-nilly.

Big safety hint: make sure your power supply is turned off, and maybe even unplugged to be sure, before wiring up your circuit. Before turning on the power supplies, make sure the voltage and current knobs are turned all the way to zero.

Capacitors can react angrily to a sudden spike in voltage, and the magic smoke inside may escape ...

Homework submission

Just a couple of things that will make grading easier for me:

1) Putting your last name in the filename you send helps a lot, so I don't have to rename everything. For example, "p_leclair_HW1.pdf" is really handy. "leclair_p_HW1.pdf" is even better, since it alphabetizes nicely I look at all the files together.

2) If you know how to do it, combining separate scanned pages/pics into a single file is good, but don't spend too much time figuring it out if you don't know how. I can suggest how to do this on various platforms if you're interested.

3) If you turn in a hard copy, I don't necessarily need a copy of the problem set itself, you can just turn in your work.

4) Include "PH102" in the subject line of the email, and possible HW1 or something like that to help the filtering.

Basically, it costs a little more time if I get 30 emails with a subject like "homework" or "physics homework" and filenames like "homework.docx" or "hw.jpg". I can sort this out very easily, I'm mainly pointing these things out because it probably isn't something you thought about. I wouldn't have either, until I started taking email homework submissions.

These are really just suggestions, I'm happy to deal with any sort of files you send. I can read pretty much any file format you can think of (that is not a challenge, btw), and keep things pretty organized, so it isn't a huge deal. The main point is: if you can save me some seconds per submission, this is nice because I have 68 students between two sections.

Just to reinforce: there haven't been any problems at all so far, even with the cell phone pics (many of you have good phones, it seems), I'm just letting you know what would help if it isn't difficult for you.

Also, thanks for the cat pictures. Nice looking cat.

Traffic for this site

Nicely periodic. Can you spot the weekends without looking at the time axis?

Neat optical trick

Your brain interprets color in funny ways.

I've got your extra credit right here

A small paper. You will need to watch a movie to complete the assignment; I'm sorry.

HW8 is out

Here you go. Have fun, it is due Monday 3 Aug by the end of the day.

Why, yes, it is a thinly-veiled attempt to get you to read the chapters ;-)

Random end of classes updates

Ok, it is the end of days ... for ph102 anyway. Several things:

1) There is no lab on Wednesday. You can have the afternoon off to study ... or whatever it is you do. I suggest studying ;-)

2) The final quiz and lab grades are now up on Moodle, as is Exam II. Homework 3 will appear sometime Tuesday evening. After that, all is left is homework 4 and the final. Recall the grade weighting from the syllabus.

3) Homework 4 can be handed in with the final exam without a late penalty.

4) Somewhere in the depths of a heinous sleep-deprivation-induced lapse in judgment, I decided that the final exam will NOT cover waves, quantum or atomic physics (i.e., this week's material).

5) The final *will* cover Relativity, Electricity, Magnetism, Induction, Circuits (ac & dc), and Optics (i.e., everything except this week's material). Study your homework, old homework, and old exams. Oh, and the book and notes.

6) The final will be, contrary to previous rumors, more like 75% multiple choice and 25% problems. It will be held at 8am, this Friday, in our normal classroom.

7) The exam II average was 89%, with a standard deviation of 8.5%. Below is the distribution for exam 2, plotted as the percentage of people choosing each question, and of those, the average score. Clearly, each question should have had a 50% chance of being chosen if they were all equal. Apparently, they were not ... certain questions were perceived as being much harder than others ...

8) There may be a review session on Thursday. Stay tuned.

9), 10) Intentionally left blank.

11) This one goes to eleven.

Math Tests

I thought this was highly relevant ... not only is it good advice for, *ahem*, certain physics tests, it is also applicable to the GREs at least (and probably the MCAT, though I never took one myself).

The part about story problems is spot on. Read them like this at first: "Blah blah blah FIVE VOLTS blah blah TEN OHMS blah blah blah WHAT blah blah CURRENT." The answer is likely to be 0.5, independent of the blahs.

At least back in my day, the GRE math was almost identical to the SAT math. And story problems haven't changed much. "As I was going to St. Ives ..." (yes, that riddle in fact pre-dates Die Hard III)

Video of today's lecture

I haven't had time yet to do any processing (say, to cut out our 10' break in the middle), or even watch it all, but here you can find the video of today's lecture, as MPEG or Quicktime. (The accompanying powerpoint slides are here.)

A couple of quick observations on this:

• The projector screen is still off-camera, so it is a bit annoying you can't see the images I'm referring to, hence the separate download. My iSight is not up to the task of capturing the whole room.
• I am frequently off-camera. I knew I moved around a lot ...
  
• The whiteboard scribblings are readable, but sometimes just barely so. I need bigger markers (wider), and I should write bigger.
• I still dislike how my voice sounds recorded, and I look like a dork with the headset on. It was easily the best way to record the audio, though.

I don't know if these videos will actually be useful or not. I can imagine after listening to me for two hours already, you would be loathe to sit through a rerun ... on the other hand, for homework solutions, or trying to remember what I said about something in particular, maybe.

Ideally: one would remix the video with the powerpoint slides I used, so both appear side-by-side, cut out the 'dead' spots, and add some indexes so you could find any particular spot in the lecture at will. Or: I could continue getting at least a few hours of sleep per night.

Better yet: check out the iTunes University. People with staff, resources, and pro technology are already doing this ...

Correlation between homework and pre-final grades

This isn't particularly shocking, but there is a 87% correlation between your homework average grade and your up-to-the-minute overall grade.

There is not a lot of hidden meaning here: if you did your homework, and did it well, you scored well on everything else by and large. We can say with (much) better than 99.95% confidence that your homework score is a good predictor of your total grade. This establishes correlation but not causation, though in this case I would hazard a guess that doing your homework in fact causes you to do well on everything else.

My current theory is that the final exam scores will follow this plot as well, supposing that it is a bit late to catch up on everything at this point. I am hoping, though, that you prove me wrong!

Special topics lecture next tuesday

On Tuesday 28 April, we have a "special topics" lecture scheduled. If you can suggest anything - related to the ph102 material, at least tangentially - that you might be interested in hearing about, let me know before the end of the weekend.

If there are several topics I think I can work up on short notice, I'll pick the one I think has the most broad appeal. If no one suggests anything, I will talk about what it is I do.

Other possibilities:

• how does MRI/PET/CAT work?
• how does your iPod work? (related to what I do)
  
• more bad movie physics
• how do semiconductor devices (transistors/flash/whatever) work?
• length scales, from nuclei to galaxies
• something you think I did a poor job explaining the first time around :-)

Leave a comment here (or email me) to vote on one of these, or suggest another topic.

And no, it won't be on the final. This one is supposed to be purely curiosity-driven, "for fun."

April is stress management month

From the CW:

"April is stress management month," said Jennifer Turner, coordinator of clinical services for the Counseling Center.

Why am I just finding out about this now? Probably my technique of "more coffee and less sleep" would be frowned upon ...

Office Hours Monday, misc.

I'll be in my office from 11-2 on Monday for exam-related questions ...

Also, this is interesting ... a lawsuit claiming that students' notes infringe on the professor's copyright. I will not comment directly, there is subtlety involved in this case ...

For the record, my notes are under an open content license. Basically, you can distribute them in whole or in part in any medium you like, without changes. That is, libre, not merely gratis, or free as in "free speech," not "free beer." If you modify the notes, or want to make them into a book, you do need my permission. I doubt you'll break the bank selling them, since they are free online though ...

Tangentially related anecdote follows, with little relation to ph102 ...

I published my Ph.D. thesis under a similar license. I had written several chapters which I though were a good review of my field at the time, and though the best thing would be to make it freely available to anyone who could use it. At the time I felt very strongly that information should be free whenever possible, without creating real or artificial barriers for those who genuinely want to learn something. If your hard work can benefit someone else, that is reason enough to do it. I still feel that way, and that is why nearly everything we do in ph102 is online, for free. When I get to it, anyway.

In my thesis (and in the notes, for that matter), I even carefully remade every figure myself to avoid using any copyrighted material whatsoever- since I had such a hard time finding figures I could freely use, why not save someone else the trouble down the road. It can be tough to find nice explanatory figures for basic things that aren't the Intellectual Property of someone or another. My aim was subversion: if I have to make my own figures anyway, give them away for free, so no one else has to go through the trouble. "Information wants to be free," so the saying goes.

So, a few months after my Ph.D. or so, I was in a conference listening to a talk, and about three slides in was one of my figures in the introduction. Six months later or so, a colleague asked me to help him write a review article. Guess where a good number of the figures came from! This was some years ago, so and things have become outdated a bit, but still every now and again at a conference, I do a double-take, and realize I'm looking at my own pictures ...

That is probably the most satisfying feeling I've had as a scientist thusfar. And that is the idea behind the notes. You're already paying to listen to me - and paying well - there is no reason you should pay a second time, or pay to share what you've learned when you leave here.

On that note, I still have quite some editing to do ...

* Paper and ink still costs money of course. Hats off the the SUPe store, who did a brilliant job, and went out of their way to keep your cost at a bare minimum.
** This post is obviously my own viewpoint, and not that of UA. Disclaimer applies.