Today's lab

was probably a bit hard for you. That is OK. There are really two reasons for this.

1. Scheduling. I chose to do relativity first, the other two classes I have to stay synchronized with lab-wise did not. My way is sort of a pain on the instructor (not following the textbook order for one), but I think the course as a whole ends up more coherent. Also, the PH106 section we're syncing with doesn't even cover relativity at all. As a result, for the first week or so the labs come a bit sooner than I would like. This will be resolved next week.

2. Realism. You walked into the lab knowing only a little bit about capacitors, and then were expected to figure out how they acted in combination - while also knowing next to nothing (on average) about the power supply and meter you were supposed to use. This probably meant you were confused at first, had to read and think a bit, and ask a lot of questions about the equipment. It is frustrating, but this is a much more realistic picture of how real experiments work - many unknowns, all you can do is be systematic and careful. It is more a barely-guided exploration, driven by your inquiring as to how things work, than baking a cake or assembling some Ikea furniture. There is never a complete recipe or instruction manual that will always work. We can't do all the labs like this - just throw you into the fire, as it were - but I think it is a good experience to just turn you loose with minimal preparation and see what you can figure out some times. We will do some 'cake baking' labs too, but doing only those gets boring.

That being said, tomorrow in lecture we'll discuss capacitors, meters, and circuits in detail, and I think in retrospect everything will make sense, and you'll have a better appreciation for what you did today.

Tomorrow's lab is a milder version of the same thing - we're going to turn you loose with various electrical components and see what you can make them do. It will be less difficult than what you did today, but will still involve an element of exploration that is really key to proper experimentation. 

If you're feeling lost

don't fret it just yet. Special relativity is probably among the most conceptually difficult material we will cover all semester, and it involves relatively subtle arguments and reasoning. (Oddly enough, the math is straightforward.)

So, if you felt a bit lost during today's lecture, don't worry, it is not at all unusual. It will take time for the arguments and really the necessity of relativity to coalesce properly for you, it probably isn't going to happen just listening to me for 45 minutes. Read through the notes (really read, don't just scan for highlighted items), read through your textbook, and don't hesitate to ask me if there is something you're not getting.

It will still be weird even when you think you understand it. The weird won't go away, but the confusion will. There is a difference - weird can still be logically consistent or even a necessity to have logical consistency.

Random Things

Thing the first: I really think the electric potential stuff will 'gel' for you quite a bit after the next lecture. We've just touched on it so far, in the next lecture we'll look at some practical problems and how to really use potential for calculations. We'll also be moving into more concrete subjects - the energy of crystals, circuits, etc. - and you'll have a little more intuition for what's going on. So, it is a lot of information at once, but be patient. There is a plan of sorts, and by exam time you'll be vastly less confused ...

Thing the second: check out the right sidebar. The 'course notes' are very extensive (nearly a complete textbook), and very close to what I follow in lecture. Following both the notes and the book is not a bad idea - if a section in the book doesn't make sense, try the notes & vice versa. They treat the same subjects slightly differently, you might find one explanation more to your liking than the other.

Thing the third: there are also many, many solved HW and exam problems you can access from the right sidebar. If you want example problems, or want to see what I've asked before on exams (the presumption that I will ask similar things is a good one), there you go ...

Thing the fourth: if you are in Dipanjan's section, we are going to have the same exam, same format. Details to follow soon ...

Availability tomorrow

I'll be around Gallalee from about 11:00 tomorrow, and available up until the afternoon final (modulo ~30min to make copies and so forth).

The exam has been made, and I worked out all the problems to make sure they were reasonable. After doing so, I tweaked a few of them to make them more straightforward ...

Remember, if you have questions about a particular problem during the exam, you should ask. Sometimes the main difficulty is just figuring out what is being asked, and that I can usually help you with.

Thoughts on the final

I posted this last year, and it still stands. Here are some of my random thoughts on the final. It goes to 11.

(1) Relax. There is no reason to be more freaked out about this exam than any other, percentages and so forth notwithstanding. You should be less scared: broadening the scope of the material necessarily means that the difficulty level for any given problem goes down.

(2) There is only one way to study for this thing: read and solve problems. You will be given all of the required formulas, memorizing them will not help, nor will memorizing tricks or shortcuts. All problems will involve the systematic application of simple principles and simple relationships, there are no tricks. Rote memorization / cramming is not useful, but solving practice problems is.

(3) Cut your losses on the one chapter you really don't think you can master in the time remaining. You'll have a choice in problems, so you can avoid certain topics if you know the rest very well.

(4) Look at the previous final exams (spring/fall semesters mainly). They mostly don't have posted solutions, but I can tell you the answers at least.

(5) Few problems I have asked you before will appear on the final. Most likely no problems directly from the notes will appear on the final. However, about half of the problems will seem eerily familiar.

(6) Relax. You will need to have your wits about you, the problems on the final will involve logically solving problems step-by-step using simple rules. They will not involve remembering an arcane phrase or formula buried in the text, nor will they have many convoluted twists and turns. Most of them involve only 1 or 2 steps.

(7) Run the numbers on your grade. The final is worth 25% of the total grade ... it can only change your overall grade by so much. Not as much as you think. I will scale the average on the final if necessary, such that it is at least 75% for the class. It is unlikely to be necessary.

(8) I like crystals and mass spectrometers and circuits. Capacitors have been done to death though.

(9) Study the homework solutions I have online.

(10) Seriously, relax. Get some rest the night before, you'll be better off well-rested.

(11) Answers/solutions to your outstanding homework/quizzes will posted soon, and will be good to study from.

Last-minute things

First: an error in the HW2 solution has been corrected; I solved #2 incorrectly ... it is fine now.

Second: There won't be any questions from Ch. 18 in your text (Ch. 5 in the notes), i.e., dc circuits. There will be questions on current, resistance, and resistivity, but not on resistors and circuits with resistors. I know I said it was fair game for the exam, but once I got to making it up, I had enough questions without digging into dc circuits. So, that's one less thing to worry about.

Third: here's a preview of your formula sheet for the exam. It may change as I find typos or change my mind about something, but it will look very much the same. You are still allowed to bring in one 8.5x11in sheet of paper of your own with whatever you want on it; this preview is meant to help you figure out what you needn't bother putting on the sheet ... (You can bring in one sheet with both sides filled, or two sheets with a single side filled, which I figure amounts to the same thing.)

Fourth: DO NOT FORGET A CALCULATOR. I will bring a few spares, since someone's calculator invariably dies on exam day ...

Finally: relax. You have been well trained for this thing, if I do say so myself :-) and you will be fine.

Final Exam

So, I've made it up now, and I estimate based on your past performance that most of you can finish it in 90 minutes or so. Some of you will finish in under 60 minutes, just barely. One update: you can choose 6 of 9 questions, not 6 of 8. One more choice than promised.

Here are some of my random thoughts on the final. It goes to 11.

(1) Relax. There is no reason to be more freaked out about this exam than any other, percentages and so forth notwithstanding. You should be less scared: broadening the scope of the material necessarily means that the difficulty level for any given problem goes down.

(2) There is only one way to study for this thing: read and solve problems. You will be given all of the required formulas, memorizing them will not help, nor will memorizing tricks or shortcuts. All problems will involve the systematic application of simple principles and simple relationships, there are no tricks. Cramming is not useful.

(3) Cut your losses on chapters you don't think you can master in the time remaining. There are only 6 problems you have to solve. Nailing 5 out of 6 can still get you a solid B without even attempting a 6th.

(4) Look at the Fall 2007 final exam and the second PH106 exam from Fall 2008 (only the parts without calculus).

(5) No problems I have asked you before will appear on the final. No problems directly from the notes will appear on the final. However, about half of the problems will seem eerily familiar.

(6) Relax. You will need to have your wits about you, the problems on the final will involve logically solving problems step-by-step using simple rules. They will not involve remembering an arcane phrase or formula buried in the text, nor will they have many convoluted twists and turns. Most of them involve only 1 or 2 steps.

(7) Run the numbers on your grade. The final is worth 25% of the total grade ... it can only change your overall grade by so much. Not as much as you think. I will scale the average on the final if necessary, such that it is at least 75% for the class. It is unlikely to be necessary.

(8) I like crystals and mass spectrometers, and quantization of angular momentum. Capacitors have been done to death.

(9) Study the homework solutions.

(10) Seriously, relax. Get some rest Wednesday night, you'll be better off well-rested.

(11) Answers to exam II will be posted soon. Full-blown solutions are probably beyond my grasp at this point, given that it is already nearly 3am.

Grades

eLearning is updated with all outstanding work, except HW7.

The "Cur. Avg." column now takes into account your dropped grades: 2 dropped labs, 1 dropped quiz*, and 1 dropped homework. This is now a realistic representation of your grade.

The final exam counts as 25% of your grade if you want to estimate what you need on the final to get a certain grade.

*Quiz 4 is dropped for everyone, unless it is higher than your lowest non-dropped grade (at which point it replaces the lowest non-dropped grade).

Relativity

Couple of random comments, since Tuesday's lecture probably seemed really tough.

(1) I think relativity is the hardest stuff we cover. We cover it first because we can make use of it later in a good way, and because it follows PH101 more logically.

(2) Particularly the first day, relativity is really bewildering. Typically, it makes a lot more sense on day 2, when we get a little bit further along and start to apply it in a concrete way. It is something like 'day 1: why things are weirder than we think' and 'day 2: shut up and calculate.' Day 2 is usually where things make more sense, or at least one just trusts the formulas we developed and tries to figure out what one can do with them.

(3) Based on the above, don't get too worried if today seemed like a rough start. It will make more sense on day 2, and the subsequent material is conceptually easy by comparison.

A few more final exam details

The final will have two parts: multiple choice, and problems. The multiple choice section is worth 75% of the exam score, the problems section is worth 25%.

On the multiple choice section, there will be roughly 25 multiple questions, spanning everything up through optics. Roughly half will be qualitative (conceptual), roughly half will require simple calculations.

On the problems section, there will be two sub-sections. In each subsection, there will be 5 problems in total, you can solve any two of them. Thus, you solve a total of four problems out of ten - two from each group. All problems have equal weight, it will not matter which ones you choose. Heavy partial credit will be given, as usual. The sub-sections of problems are not grouped in any logical fashion, the five problems in each section will be a mix of topics.

Your final exam grade will then be calculated according to (exam score) = (multiple choice score)*0.75 + (problems score)*0.25. A certain degree of risk management comes into play here ... do not spend 75% of your time on something worth 25% of the points, and similarly do not spend 5% of your time on something worth 25% of the points. Pace yourself, and watch the time.

You will be given a formula sheet, you are additionally allowed to bring in two sheets of 8.5x11 inch paper, containing any information you like.

The exam will be 8-10:30am on Friday, in 227 Gallalee (the lecture hall). I suspect you will need the entire 2.5 hour period. The exam will be curved, if necessary, to ensure a reasonable class average.

Study your homework sets and exams, as well as the old ph102 exams and quizzes. And get some sleep before hand ... if you have been following things so far, there will be no surprises.

ADDENDUM: if you are allotted extra time for exams through testing services, and would like to exercise this option, we need to talk as soon as possible about scheduling.

Sudden change of plans ...

I think we need to take a breather. You all seem almost as tired and jagged as I am ;-)

Tomorrow, rather than covering the lenses material as planned, we will be reviewing for the exam. I think right now you would benefit more from solidifying the material we already covered, rather than moving relentlessly forward. We'll pick up optics again on Friday.

So here's the plan for Thursday ... about 9 hours from now: I'll review briefly the material relevant to the exam. I will also bring some exam-like problems to solve and work on the board. You'll come with questions, and problems you want to see a solution to. Anything is fair game ... so long as it is related at least tangentially to the exam.

I had more or less built one extra day into the schedule from the beginning, just in case, for things like this.

I suppose this means that if you think you are ready to just completely rock the exam, tomorrow could be a waste of time. Probably, though, in my heavily sleep-deprived state, I will let some important hint about the exam slip. One never knows.

Exam I results

Well, the exams are graded. You will get them back tomorrow, and we will go over the solutions.

No scaling was necessary - the average was 84.6%, with a standard deviation of 12.2. Very well done, better than expected. Here is a histogram, of sorts:


Since the exam was multiple choice, 20 questions long, each question was worth 5 points. Thus, saying the thing above is a histogram is being a bit too fancy; it is really just a plot of how many people got each score. Basically: many of you rocked the exam, and clearly studied. A smaller number of you did not rock the exam.

Now, if you are on the low end of the distribution, keep in mind that each exam is only 15% of your grade. Your homework, quizzes, and labs are all worth 15% each at the end of the class ... so a lower than expected exam score can easily be made up by doing well on the homework.

Basically: don't panic. It is still early enough. Be diligent about labs and homework, and things have a way of working out.

Below is a breakdown of the average score by question. Clearly, #20 was not your favorite. I suspect the problem was partly confusion of metric prefixes, and partly forgetting to take a square root ...



Perhaps not surprisingly, the questions I worked out in class today were quite easy for all of you ... a little present for showing up to lecture on the day of the exam, I guess.

And, by the way: we will go over new material tomorrow ...

Thursday, 10 July 08

I wasn't quite satisfied with what we've done with relativity so far, and so I will spend half an hour on it again tomorrow. We hit all the high points, but have not done enough example problems to bring it all together, IMHO.

After the first 30mins or so, we'll start electrostatics. By and large, students find this much less conceptually difficult than relativity. If it feels like you're being thrown in the deep end so far, you are! But relax: it will pay off in the end. Relativity will be useful to us very soon, I promise. Treat the first two days as painful but necessary background for later goodies.

Anyway: the plan is 30mins relativity (incl. homework problems), the balance goes to electrostatics.

Lab: some of you already emailed me a paper. Good work: for doing two sessions' work in one, you can skip the lab today. Sadly, this was a one-time event - we have no other two-session labs. If you did not finish the paper yet, 6pm tomorrow is zero-hour.

Printed notes: any luck at the SUPe store? Anyone want hard copies?

Random homework hints:

5) This is just velocity addition/subtraction in disguise. The rest is there to distract you. Just like on the MCAT, e.g.
10) Wikipedia is your friend. But ... don't be going on about light cones and such unless you can back it up. Keep it simple :-) I'm in a generous mood: let's say that 3/4 of a page is close enough.

Homework 12 solutions

Here they are, almost complete. Only the one about the ring of charge is not yet complete, but I assure you that particular problem will not show up on the final exam.

For more last-minute fun, here's a draft of the formula sheets I'll be including on the final. This is not final, has not been proofread, etc., but gives you an idea of what to expect.

Also: relax. If you've been going to class and following the homework/quiz solutions, you have nothing to worry about. Most important will be to keep your cool and use your time wisely on the final - don't get stuck on any one question for too long, and don't panic.

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."

Fun

http://xkcd.com/397/

No recitation on Friday 14 March ...

... I mean, let's be perfectly honest with ourselves.

Finals are graded

Let the flood of emails begin :-)

[really, it is ok to email me or drop by and inquire about the final.]

It wasn't that bad in the end, and I scaled generously. The multiple choice average was 74.5%, and the problems average was 60%. I scaled each part (MC and problems) separately to come out to an 80% average with 12.5% standard deviation.

In rough terms, that means if you got a 50% overall, you still passed. Yes, it was that hard ... I consider a raw score of 50% a suitable passing grade, and a raw score of more than 80% worth an A on the final.

There will be lots of detail on this tomorrow, and I should have final grades posted by tomorrow night. The early numbers tell me that on average 40% of you actually improved your overall grade after the final exam.

So rest easy! No one dropped by even a full letter grade after taking the final.