Tuesday, November 30, 2010

PH253 last lecture: computer logic & memories

It seems flash/ram/etc has won the day, so my last lecture of the semester will be on computer architecture, logic, and memory from a physics-y point of view. Invite your friends ;-)

The rough plan will be this:
  • What is our current high-level computer architecture?
  • How does one make memory/logic? What components are required? How do they work?
  • How do we currently build logic and memory?
  • How do (s/d)-ram and flash memories work?
  • What are the future prospects/promising new technologies?
  • Is Moore's "law" really in trouble? (Spoiler: it is not a law, and not yet.)
I think this will make a nice consistent logical flow, and all these topics are accessible with the physics we've covered. Time permitting, I would add:
  • A brief overview of how hard disks work
  • A brief overview of how mram might work (spoiler: it isn't ready yet)
  • Energy requirements/limitations for computation
This last lecture will be mostly 'show & tell' via powerpoint - almost no equations, mostly descriptive, but we've covered all the physics you need to understand these things. None of it will be on the final exam (neither will the material on LASERs from today).

Tuesday's lecture, evaluations

Today, in about 10 hours, we will figure out how lasers work. That's our last regular lecture, Thursday's lecture is still up to you, to an extent.

If you don't like lasers, here's another reason to attend: we'll do the department's discursive 'free-form' course evaluations at the end of the lecture. A good chance to give some (totally anonymous) feedback on what you'd like to see done differently, or not. I really do read all the evaluations and adapt based on the feedback.

The discursive evaluation is in addition to the online evaluation form for course evaluation you should have received email about already (probably a couple of times). Currently, only 26% of you have done the online evaluations, so please, please check your email (search for SOI if you have a lot of email) and fill out the college-wide evaluation. It takes 10 min at most, it is completely anonymous, and like the discursive evaluation, I take them very seriously when planning my courses.

PH253: Final Exam

Note that our final exam is Friday, 10 December from 8-10:30am. If you have already booked travel home before Friday, 10 December ... well, we have a problem, and we should talk.

Basic rules:
  • 12 problems, you choose 6 to solve.
  • If you do more than 6, I'll grade the best 6.
  • Comprehensive - basically everything through last week will be on the exam (i.e., nothing on this week's lectures).
  • Formula sheets will be given - they will be an agglomeration of the formula sheets from the first two exams, plus whatever is necessary from the material after exam 2.
  • You can bring 2 of your own sheets of 8.5x11 paper, double sided (or 4 sheets single sided).
Topics, roughly
  • Relativity
  • Radiation (accelerated charges, blackbody)
  • Photoelectric/Compton/photons
  • Wave-particle; de Broglie
  • Schrodinger's equation, 1D potentials
  • Bohr atom
  • Hydrogen in 3D
  • Angular momentum & spin
  • molecules & bonding
  • Multi-electron atoms & the periodic table
  • periodic solids, energy bands, metals-insulators-semiconductors
  • particle statistics
Definitely not on the final, but covered in class:
  • LASERs
  • variational method
  • p-n junctions (diodes), transistors
  • whatever we do for the last lecture
Gaming the system:
  • I listed12 topics. There are 12 problems. You have to solve 6 of them. Logically, you are responsible for only half the material. Pick your half carefully - if there are 1 or 2 topics you are sure you will not 'get' in time, skip them.
  • I will reuse old HW and exam questions, from this semester and last semester. Most questions will be new, but there will be a few recycled ones.
  • Letting you bring your own sheets is often a trap. If I let you bring all that in, how much could it really help you? You might get lucky printing out old exam/HW questions, but the odds are not great.
  • Work old HW/exam problems. The exam is about solving problems, so you should do that to prepare. I'm also likely to ask the same sorts of problems I have before, if not the same thing exactly.
  • Ask questions during the exam! I will often give out a startling amount of information if you're brave enough to ask during the exam.
  • Sleep. You will need your wits about you - the final will be more about cleverness than regurgitation, so cramming the night before will will probably hurt more than it helps. That being said, arrive properly caffeinated. I will. I will probably also bring a thoroughly unhealthy breakfast snack for you.

PH253: one more extra-credit possibility

One last chance for extra credit, the procedure is much like the last time. Due at the start of the Final exam.
  1. You watch one of these lectures (about an hour each). They are very good, and aimed at a lay-audience (you are well above that, having had at least 3 physics courses so far**), and Feynman is generally very entertaining.***
  2. You write me 3 page (8.5x11 in paper, 1.5 inch margins, 12pt font, single spaced) paper covering
  • Two new things you learned from the lecture (or things you understood better)
  • One way the lecture tied in to PH253
  • One way the lecture tied in to your major/field of study
  • One way the lecture tied in to everyday life
Do this, and I give you as much as +2% on your overall grade at the end of the semester, depending on quality of your writeup.* This extra credit opportunity requires a bit more writing (3 times as much, I guess), but on the other hand, the other one required you to actually attend something. I figure it about even.

To give you an idea of what 2% means:
  • There will be about 10 HW sets. Each is worth about 1% of your grade. This is 2 free HW sets. Typing up a three pages should and watching a video should take a minuscule amount of time compared to two of my HW sets :-)
  • Each hour exam is 30% of your grade, each question on the exam about 6%. This is like adding 3 points to your lowest exam question.
*If you are a non-native English speaker, this will be taken into account. English grammar and spelling is very silly.
**More like 'at least 2.7', since 30% of your PH253 grade is still to come ...
***Also, thanks to Bill Gates for making these lectures available ...

PH253: more grades on Moodle

Just uploaded HW8 grades, which leaves only HW9 outstanding at the moment. I'll try to have that by the end of the week.

Tuesday, November 23, 2010

PH253: last lecture

We have two lectures left. One is Nov 30, when we'll finish our discussion of particle statistics and figure out how lasers work. The second is Dec 3, our last class meeting.

I have not decided what I would prefer to do on Dec 3 myself yet, but as promised I'm open to any (reasonable and physics-related) suggestions for topics. Anything at least tangentially-related to the material we've covered I'm willing to give a lecture on. You can email your suggestions, or leave comments here, but just about anything goes. I will indicate if I think the topic you suggest is inappropriate or too detailed to explain clearly in one class.

My own suggestions, in no particular order:
  • more on transistors & semiconductor electronics
  • information storage technologies (hard disks, ram, flash, etc.)
  • two-level systems & resonance
  • applications of particle statistics (chemical kinetics, diffusion, etc)
  • crystals, geometry, & diffraction
  • magnetic materials
Don't feel confined by this list of topics, they are just a few things I would have liked to have covered if there were more time.

PH253: notes from today

Today's lecture was mostly drawn from the Feynman lectures, vol III, ch. 3-4. My own notes from last semester are here. (I didn't change much this time around.)

Monday, November 22, 2010

Student opinions of instruction

Reminder, you should be doing your course evaluations (student opinions of instruction, or SOI) right about now.

College-wide course evaluations are completely online. You should have received email instructions by now, and have until 5 Dec to complete your course evaluation. We take these very seriously, they are anonymous, and we cannot see even the aggregate results until well after your grades have been posted (at no point, ever, can we see who posted what comment, it remains totally anonymous).

PH253: last homework set

Here you go. Last HW set, due on the last day of class. For those of you attending the last few classes, we will go over the tougher problems.

Keep in mind I drop one homework set, so if you've done them all so far ...

Monday, November 15, 2010

PH253: Moodle grade update

Moodle is up to date through HW7 now (as well as including late HW and exam 2 alterations).

Wednesday, November 10, 2010

PH253: what is the point of HW9?

This week's homework is difficult, I grant you that, but not without reason.

*The first two problems are really our first stab at calculating the properties of real, everyday, useful materials (not that H is not useful or interesting, I guess). The vibrational frequency you'll calculate for KCl matches experiments amazingly well, in spite of the simple model potential used.

* The variational principle is something you will come across again, probably in mechanics (PH301/2) if not quantum. It is more or less a powerful way to come up with a best guess solution to a problem without actually solving it, and therefore powerful. There exist even more powerful methods commonly used in Chemistry and Physics for calculating the electronic properties of materials (e.g., Hartree-Fock, Density Functional Theory), but they are far more difficult. Should you encounter them, you're likely to be thrown in the deep end; the point of problems 3&4 is to give you a taste of how to handle systems which cannot be treated exactly without all the mathematical baggage that can obscure the essential simplicity of the method.

* Coupled oscillators can be used to explain a really ridiculous number of phenomena. In Thursday's lecture, we'll used a coupled oscillator model to (more simply) re-derive all of what we've learned of bonding, and cast it in a form that looks suspiciously like masses & springs or coupled LC oscillators. With this new approach, we'll be able to extend our analysis to the case of periodic solids (like semiconductor crystals, leading us to transistors and such). We'll be able to explain why some stuff is electrically conducting and other stuff is not, and why real materials behave the way you do. Problem 5 is meant to get you thinking about how coupled oscillators work as a preface to that lecture. It also gives you some hints on how one can spectroscopically identify different molecules (look for radiation emission/absorption matching the vibrational frequencies) or when molecules are adsorbed on a surface, e.g., in catalysis (new vibrational modes show up compared to the original molecule).

So, in short (if it isn't too late for that), think of this problem set as a preview of what's to come - both how we'll figure out how to calculate the properties of real materials, and what you're going to be up against in later courses. Most of what we've done the last month or two has been leading up to this.

Tuesday, November 9, 2010

Supplemental notes on chemical bonding

The variational principle and chemical bonding. These are some scanned notes from when I was an undergrad, related to last Thursday's and today's lectures.

Monday, November 8, 2010

PH253: Exam 2

Exam 2 grades are now on Moodle. You'll get them back tomorrow.

Friday, November 5, 2010

PH253: HW9

UPDATE: small change to 5c: you can assume the masses and springs are equivalent.

HW9 is out, due next Friday 12 Nov. There are only 5 questions, but you will not like them. ;-)

There will be plenty of hints in the coming week. You will need to recall a bit of mechanics.

Thursday, November 4, 2010

PH253: grades

Moodle grades are now updated through HW5. Your overall average drops the lowest HW set.

Later today I should have it updated through HW6 at least, and over the weekend Exam 2 will be there.

Tuesday, November 2, 2010

PH253: notes from the last week or so

Here are some scanned notes (from last semester) on what was covered while I was away. The parts where I refer to homework are from last semester's homework 8. These are more or less the notes I gave Dr. Mankey to use; any errors are mine.

If you think your electronics labs are too tough

These guys had it worse. Constructing a radio receiver from what could be scrounged from a POW camp. Including building their own resistors, capacitors, and rectifiers. Pretty crazy.

Monday, November 1, 2010

HW7 solutions / HW8 due date

HW7 solutions are out. This time, we heavily abuse Wolfram Alpha to avoid a great deal of tedium.

HW8 is due tomorrow, Nov 2. I did not note the time that it was due, but it is the usual 11:59pm ... so you have about 25 hours to go yet.

Good thing, since apparently many of you are affected by a power outage at the moment ...

PH253: Exam 2

Exam 2 is this Thursday, Nov. 4 during the normal class period. The rules are basically the same as last time:
  • You can bring in one sheet of normal 8.5x11in paper front & back, or two sheets using one side only on each. 
  • You will also get a formula sheet with the exam.
  • There will be 6 problems, you choose 4 to solve.
The coverage for the exam is, referring to your textbook sections:
  • 2.4.4-8, 2.5 Wave functions, Schrodinger, etc.
  • 3.2.1 Bohr model
  • 3.3 Hydrogen
The relevant homework sets from this semester are HW4-7; additionally HW4-7 from this past spring are relevant (as is exam II and the final exam from this past spring).

I will draw all of the problems problems directly from your homework from this semester and the homework from last semester listed above (though in somewhat abbreviated form).

Study those sections of the text and your notes, look at the HW sets mentioned, and you will be fine. It is extremely unlikely that practice problems will appear.

I will try to post the formula sheet tomorrow (Wed) so you know what you don't need to bother including on your own sheet.

PH253: HW8 #2

Check it. Good idea to google the phrases I put in italics.