Modern Physics @ UA

Lab schedule

2011-02-07T16:21:00.000-06:00

For your reference:

PH255 Lab Manual

2011-01-24T01:09:00.000-06:00

Here is the PH255 lab manual [49Mb PDF], with procedures for all experiments, the syllabus, and plenty of other useful information. You don't need to print anything out before class, I will have the lab procedures printed for you when you arrive. Please read the syllabus, course information, safety rules, and other introductory material as soon as possible.

UGrad research conference

2011-01-13T13:10:00.002-06:00

RESEARCH AND CREATIVE ACTIVITY CONFERENCE APPLICATIONS — Faculty are requested to remind undergraduate students of all majors that they are invited to enter UA’s annual Undergraduate Research and Creative Activity Conference scheduled for April 11 at the Bryant Conference Center. Students can compete for cash prizes and earn practical experience in defending or performing their work before judges. To participate, undergraduate students must register their projects by submitting application forms and abstracts describing their projects by March 7. Visit http://www.osp.ua.edu/UndergradResearch.html for an application and details.

PH253 final grades, mark 2

2010-12-14T00:45:00.000-06:00

After going through the whole spreadsheet and looking at the final exams a third time, I decided to revise upward the partial credit on a couple of questions on the final. This will affect a lot (but not all) of you, depending on whether you chose to do those problems or not, and depending on what exactly you did. For some of you, the change was enough to affect your final grade.

I also went through everyone's final exam for a third time, and on a couple of exams I found that I had misunderstood the answer given, and you were owed more points.

Long story short, some grades needed to be revised.* Once I check my spreadsheet for what must be the 15th time, I am going to upload really final grades later this evening. I've been obsessing about this for three days now, but I think finally have gone over everything enough that I think it is consistent and fair.

*I didn't revise anyone's grade downward. If there was a grading error in your favor, it stayed.

PH253: preliminary grades on myBama

2010-12-13T02:27:00.001-06:00

I've posted "final" grades on myBama, subject to the following qualifications:

I have to check my spreadsheet thoroughly to be sure all my calculations are correct.
I will have one more look at your final exams if you are on the borderline between two grades (I've graded them twice thusfar).
Some of you might still sneak in an extra-credit assignment or late HW by the end of Monday. (HINT)

So, I may have to make revisions after I review everything again, but as of right now everything seems to be in order. If you feel there is a mistake, contact me ASAP. Ditto if you want to know your grade breakdown.

Overall, I think most of you will not be surprised by your grade - not many of you moved up or down greatly based on your final exam score. (The class average was 0.76% higher after the final, the final exam average was 82%.) Notably, however, a couple of you managed to pull out a passing grade based on a very impressive showing on the final, which was nice to see.

Anyway, I hope you enjoyed the semester, I certainly did.

PH253 Final exam pro tip

2010-12-09T23:03:00.001-06:00

Pro tip: a problem might look on first sight just like one you've seen, but you still have to read it all the way through to make sure.

I say that since I'm seeing that same mistake again & again on HW9 ... the second problem was nearly like one from last year, but the second part was different in a crucial way. By "different" I mean "not even remotely close."

Let's recap: when you see a familiar-looking problem tomorrow, it might be a trap. Make sure I haven't changed anything key before you just go solving stuff all willy-nilly.

And, a bonus pro-tip: don't forget your calculator. There may actually be numbers other than pi and 2 on the exam. I think a 7 got in there while I wasn't looking.

PH253: server issues

2010-12-09T09:40:00.004-06:00

UPDATE 2: with the server being down, Moodle is also down until further notice. Hopefully it will come back up some time today. Also, a draft of the formula sheet for the final.

UPDATE: HW and Exams mirrored here. The additional notes as well (well, most of them, until I hit my quota on bama.edu. Lame.)

For what I hope to be a short while, old HW/exams/etc are unavailable, owing to some script kiddie messing with the server I'm using:

I just got word that the machine that runs the faculty websites has been hax0red, so we have to take it offline till we can figure out what happened.

I will try to get a mirror up later this morning.

PH253: HW10 solutions

2010-12-09T01:13:00.001-06:00

I have HW10 solutions ready. Given the end-of-semester craziness, I know quite a few of you will turn HW10 in late and take the hit on points. That's fine by me, it is your choice.

Because of that constraint, I had planned to not post the HW10 solutions publicly, but give them out by email to anyone who had already turned in HW10. The idea was that you wouldn't get to see the solutions until I saw your completed HW set.

Of course, that idea was hopelessly naive, and probably just punishes the people who need the most help.

So, here are the HW10 solutions. I will still accept HW10 up through the final exam, minus the usual late penalty. Remember that I drop the lowest homework.

PH253: 8am exams suck and we can't do a thing about it

2010-12-09T00:11:00.001-06:00

So our exam is 8am this Friday. That really sucks, and there is nothing we can do about it. Here are some thoughts about surviving the exam:

Sleep the night before. All-night cramming may help you learn a few new things, but on a problem-based exam it is critical that you are able to think clearly and quickly. Zoning out because you're tired works against that very strongly.
Use a buddy system if you're not a morning person. Seriously. Two different times I have actually called students on their cell phone to get them out of bed after the exam started. Call each other in the morning so you don't oversleep.
Don't bother memorizing stuff. I want to see if you can think & solve problems, so you'll have all the formulas you need.
Do ask questions during the exam. If it isn't 100% clear to you, ask for clarification. I may or may not be able to answer your question, but it can't hurt.
Do be explicit about showing your work, and turn in anything you wrote on. Partial credit is key. If you are stuck on how to finish a problem, at least describe in words what you would like to do, that's worth something.
Try not to get stuck on any one problem, since you will be somewhat pressed for time. (You will have more than enough time to finish if you work carefully and quickly, but if you get stuck for 15min on one problem, that may not be the case).
Use your formula sheets for example problems, notes to yourself, or a guide to what various formulas are for (and what they are not for). You'll have a sufficient formula sheet, but that only helps if you recognize the formulas ...
Remember that Wolfram Integrator will not be there to save the day on the exam, so remind yourself how to integrate the hard way ;-) Anything beyond basic polynomials will be on the formula sheet.

As I have more random work-avoiding thoughts, I will post them here ...

PH253: Exam 2 solutions

2010-12-08T23:05:00.004-06:00

Just realized today after one of you emailed me that I never posted Exam 2 and its solution.

Here you are. Let me know if you find any errors or need further clarification on any problems.

Also, last semester's final with solutions.

PH253: final exam

2010-12-08T11:30:00.001-06:00

I've decided to make it easier on you for the final, at least in terms of what you need to study.

The final exam questions will be drawn entirely from exam and homework problems from this and last semester, including last semester's final exam. (Just like I did for the last exam.) All I'm going to do is take old HW and exam problems, change some quantities or what I'm asking for, strip them down to an appropriate length if necessary, and recycle them. [Update: by exam problems, I mean the actual exam, not the sample problems.]

Some HW/exam problems are too long for the exam. Those problems will be shortened (perhaps only asking part a out of several parts). Some HW/exam problems involve too much time-consuming math for an exam, those problems will be modified to be less tedious.

So, there you go: all you need to do is understand how the old problems are worked (they will not be used verbatim, so copying them is of limited utility), and you are all set.

Again, you can bring in 2 formula sheets - either 2 sheets front & back, or 4 sheets with one side only. I'll provide all the basic formulas you need.

And, as a reminder, the final is this Friday at 8am in the usual room.

PH253: HW10 #2

2010-12-03T11:22:00.000-06:00

Here are a couple of hints.

Hint the first.
Hint the second.

Slides for 2 Dec 2010 lecture

2010-12-02T01:18:00.001-06:00

UPDATE: the revised slides I actually used are at the same link below. Not many changes.

Here is an outline of tomorrow's lecture. My first draft of the slides are here, 15Mb PDF. Given that it is the second-to-last day of classes, I suppose you can check these out and decide whether to come or not ;-) For you EE-types, a lot of this stuff (like the truth tables and logic gates) is either the familiar subject of your recurring nightmares, or it will be soon.

The outline, as of now:

basic computer architecture
memory

reminder: how transistors work
FLASH memory
S/D/MRAM basics
memory architecture

logic & computation

how to implement logic & computation
logic gates
building gates from transistors/switches
computation example: comparison, addition

information physics

energy requirements & thermal stability
mechanical, electrical, and magnetic storage
losses per cycle
the safety of Moore's "law" and fundamental limits

Time permitting (probably not): hard disks

overview of operation
media (analogous to CD/vinyl)
reading & writing
positioning & mechanical
why magnets?
history & recent boom times
fundamental limits approaching

No, this is not on the final.

PH253 last lecture: computer logic & memories

2010-11-30T23:08:00.000-06:00

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

2010-11-30T01:57:00.000-06:00

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

2010-11-30T01:47:00.000-06:00

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

2010-11-30T01:30:00.001-06:00

One last chance for extra credit, the procedure is much like the last time. Due at the start of the Final exam.

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.***
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

2010-11-30T00:42:00.002-06:00

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

PH253: last lecture

2010-11-23T13:09:00.001-06:00

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

2010-11-23T12:54:00.000-06:00

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.)

Student opinions of instruction

2010-11-22T23:23:00.000-06:00

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

2010-11-22T13:48:00.000-06:00

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 ...

PH253: HW8 & 9 solutions

2010-11-16T01:05:00.000-06:00

Partial HW8 solutions (numbers 1-4 only have answers) and full HW9 solutions (rather detailed) are out now.

PH253: Moodle grade update

2010-11-15T00:27:00.002-06:00

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

PH253: what is the point of HW9?

2010-11-10T00:40:00.000-06:00

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.

Supplemental notes on chemical bonding

2010-11-09T10:27:00.000-06:00

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.

PH253: Exam 2

2010-11-08T23:41:00.002-06:00

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

PH253: HW9

2010-11-05T10:14:00.001-05:00

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.

PH253: grades

2010-11-04T10:09:00.002-05:00

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.

PH253: formula sheet

2010-11-03T21:02:00.002-05:00

Same as last semester, more or less.

PH253: notes from the last week or so

2010-11-02T08:17:00.000-05:00

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

2010-11-02T00:12:00.000-05:00

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.

HW7 solutions / HW8 due date

2010-11-01T23:02:00.000-05:00

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

2010-11-01T10:21:00.002-05:00

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

2010-11-01T10:09:00.002-05:00

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

PH253: HW8 is out

2010-10-20T12:24:00.000-05:00

Here you go, due Nov 2. I'll be back in town on Oct. 31 and reading email for last-minute questions, and around on Mon Nov 1 all day.

PH253: help on HW

2010-10-14T15:01:00.004-05:00

I uploaded some new files here that will be of great utility.

UPDATE: on problem 3b, those should be x's not r's

Also, some useful bits from hyperphysics:

Hydrogen energies & levels:

http://hyperphysics.phy-astr.gsu.edu/hbase/hyde.html#c2

Spectrum:

http://hyperphysics.phy-astr.gsu.edu/hbase/hyde.html#c4

Quantum physics topics:

http://hyperphysics.phy-astr.gsu.edu/hbase/quacon.html#quacon

Schrodinger & Hydrogen concepts, Wave functions & plots:

http://hyperphysics.phy-astr.gsu.edu/hbase/quantum/schrcn.html#c1

http://hyperphysics.phy-astr.gsu.edu/hbase/quantum/hydcn.html#c1
http://hyperphysics.phy-astr.gsu.edu/hbase/quantum/hydwf.html#c1
http://hyperphysics.phy-astr.gsu.edu/hbase/hydwf.html#c1

PH253: HW6 solutions

2010-10-11T12:52:00.002-05:00

Here.

PH253: HW7 is out.

2010-10-11T12:49:00.002-05:00

Here you are. Due friday.

Make your own spectrometer / misc

2010-10-09T02:09:00.000-05:00

This is awesome. Cell phone spectrometer ...

In other news: I've been unavoidably detained by advising issues the last day or so, but I will be updating Moodle grades, putting out HW6 solutions, and posting HW7 over the weekend. HW7 will not be due until ~Friday next week since I'm delayed in posting it.

Tuesday, we will look at the angular parts of the hydrogen atom solution we ignored so far, and figure out what p, d, and f orbitals are all about. That will run in to Thursday, but by the end of the week we'll have a good understanding of atomic orbitals, ideally.

PH253: Public talk

2010-10-05T01:17:00.001-05:00

Dr. Orzel has been nice enough to post his slides, so if you were not able to make the lecture, you can complete the extra credit assignment by reading his slides and sample book material. Write a page on what you learned.

PH253: Physics help desk

2010-10-05T00:05:00.001-05:00

Good news everyone, I've negotiated with the PH10x TAs, and they have agreed that it is OK if you come by the physics help desk for PH253 homework questions.* You can find the help desk hours here. The following TAs explicitly agreed to help with PH253 questions:

Lei Lu, Zachary Burell, Arindam Das, Jason Carson, Chockalingam Sivakumar, Sahar Keshavarz, Christopher Sterpka, Andrea Chaney

I didn't hear back from a few of the TAs when I asked if it was OK for you to come by, but the list above covers most of the available help desk hours. (I said that a lack of response would be construed as a 'yes' on their part though.) I agreed to send them the HW solutions in advance each week so they can better help you.

*Previously, the help desk was only for 100-level physics, but I asked if they would expand their repertoire.

PH253: Unsavory HW6 typo

2010-10-01T01:22:00.000-05:00

Indeed, you are right: in problem 1 the width of the well is 2a, not a as I listed originally. The well extends from x=-a to x=a, and has V=0 over that interval. For |x|>a, the potential is infinite. That is why the normalization constant is 1/sqrt(a), not sqrt(2/a).

I've corrected that on the problem set, available at the same place.

Physics tutoring

2010-10-01T00:03:00.000-05:00

Two options:

1) I am going to negotiate with the grad students running the physics help desk to let you go to their hours for help. They are only expected to help out with 100-level physics at the moment, but I think they'd be happy to help. Presume you can go to their office hours listed in the link above unless I tell you otherwise ...

2) The physics student society runs study sessions every Sunday evening at 6pm in 109 Gallalee. It is not organized per se, but a group of physics students that get together to work on homework collectively. A lot of them are upper-level students who have already been through PH253, so they can help. I've talked to them, and they are happy to work with anyone who shows up. The main entrance is locked on Sunday, but usually they will have someone manning the quad-side door periodically to let people in. This might be the even better option, sometimes getting some help from someone who was in your position not so long ago is the best.

Public talk this evening

2010-09-30T23:57:00.000-05:00

We had a good turn out, I saw quite a few of you there. I though it was a great talk, particularly relevant to what we've been covering lately (down to the fact that he used some of the same images/videos I've posted here). I really liked the football throwing explanation of particle tunneling ... it is important to know your audience.* Thanks for making a good showing for Dr. Orzel!

If you couldn't make either of his lectures today, you can still do the extra credit assignment. The first chapter of his book (and a dramatic reading of chapter 3) are available here. Chapter 1 discusses the wave particle duality (which we spent quite a bit of time on). In lieu of attending the talk, you can read it and write me a page about what you learned from it according to the previous rules. It is a good read, and I highly recommend the whole book. (And no, I don't get anything for saying that, I met Dr. Orzel for the first time today.)

*That's not to say that my brown bottle explanation of tunneling this morning was making a comment about what you do in your spare time, but it seemed like an everyday thing you could all at least imagine, even if lacking the requisite first-hand experience. I clearly need more football-based explanations.

PH253: HW6 is out

2010-09-30T00:32:00.000-05:00

Due next Wednesday ...

Also, a nice applet for visualizing wave functions.

PH253: Wave functions

2010-09-29T23:49:00.002-05:00

Hyperphysics is good stuff. Good example calculations/solutions and explanations of Schrodinger's equation.

Everyday life is basically understood

2010-09-29T11:24:00.000-05:00

Interesting couple of posts.

One.
Two.

The basic argument is that while everyday phenomena can be hideously complex (turbulence, for example), the basic laws governing them are completely understood. There is no everyday example of something that violates quantum mechanics or relativity, you have to go well beyond the everyday to find situations where we don't even know the basic rules that apply.

Of course, knowing the basic laws (i.e., equations) is one thing. Solving them is completely another, plenty to keep scientists gainfully employed for some time to come.

PH253: Exam 1 scaling

2010-09-29T01:25:00.001-05:00

Long story short, it didn't really work out to simply add points to everyone's score or take the best 4 of 5. I suppose this is a common theme if you read the news, but either of those benefited the grade-rich quite nicely, but did little for those of you who really needed a boost. Luckily, our problem has a nice solution.

Our exam had an average of A=72.46% and a standard deviation of s=22.30%. The former is too low, while the latter is too high - the average should be a bit higher, but more importantly the spread was way too large. What I wanted to do was map your grades to a more reasonable distribution, such that most of you ended up in the middle or above, and not too many were well below 60% or so. There is a mathematical procedure for mapping one distribution to another, probably familiar to those of you who have taken statistics. To start, I calculated what is called a "z score", or "standard score," which is basically how far from the average you were relative to the standard deviation:

z = (your score - A)/s

This tells you how you did relative to your classmates, essentially. If you were 1 standard deviation below the mean (so a score of 72.46-22.30=50.16), your z score is -1. The higher the z score, the more above or below class average you were. I used this score to calculate a new distribution based on a desired class average of A'=78.5% and standard deviation s'=18%, making your new score

(your scaled score) = z*s' + B

So, if your original score was 50.16, your scaled score is (-1)*(18)+78.5=60.5. Basically, the effect is to move scores well below the mean toward it, while scores well above the mean change little. Another way of thinking of it is that your score is tied more to how you did relative to your classmates than to a particular average score. In the parlance of our system, you would call this 'curving' the test.

Everyone gains points in this scheme, but those farthest below the mean gain a bit more. The resulting distribution looks like this (click for larger):

The number of you with A's stayed about the same, but there are more B's and C's, and (importantly) the long tail of lower grades has moved up. It is still a slightly wacky distribution, but quite a bit better, and I think more representative of how you really did.

Let me know if you have questions. The Exam 1 grade you see on moodle (see previous post) is this scaled one, and it should be much happier than your raw score. Again, it might not be as good as taking the best 4/5 questions for some of you, but this was I felt the way to be most fair to the class as a whole.

PH253: online grades

2010-09-29T01:06:00.001-05:00

I now finally have the system set up so you can log in and see your grades (HW1-3 and Exam 1 right now). Since I am still young enough to be idealistic, I'm using an open source system called Moodle. Apparently you still have to pay if you want a sensible name. Instructions below the jump ...

1) Go here: http://faculty.mint.ua.edu/~pleclair/moodle/
2) Click on "Introduction to Modern Physics Fall 2010"
3) Then, to log in to the system:

Your username derived from your bama/crimson email address

If your official email is "jdingus@crimson.ua.edu" your username is "jdingus".

If you have a @bama address, perform the analogous string operation.

Your password is the last four digits of your CWID. You can change the password if you like after logging in. In fact, this is an awesome idea. Please change it right away.

Once you have logged in successfully, you should be at the main PH253 course page. There are a great number of things on this page, most of them are not useful. I'm really only using this thing so you can view your grades. Facebook, blogger, email, and IM handle the rest well enough.

From this main page, you can access your grades. You should see a link for "Grades" on the left-hand side of the page, about halfway down, under "Administration." For that matter, you can change your profile, create a little blog or discussion board, or all sorts of other things. All your information is safe - no one else can see your grades/email/etc. The data is stored in an encrypted file on a secure server.

Any feedback you have on this system is helpful. Let me know if it works ... Right now, the first three homework sets and your exam scores are there. (Please check to make sure that is true ...)

Finally: details on how the exam scores were calculated will be posted shortly, I have scaled the exam a bit. Basically, the scaling adds up to 15 points to your exam, based on your score relative to the mean.

PH253: Extra credit possibility

2010-09-29T00:37:00.000-05:00

I posted last week that we'll have a special physics lecture Thursday evening. I think it will be really fun, and directly relevant to our course material. So here's the deal

You attend the lecture.
You write me 1 page (8.5x11 in paper, 1.5 inch margins, 12pt font, single spaced) covering

One new thing you learned from the lecture
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.*

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 single page should take a minuscule amount of time compared to my HW sets :-)
Each exam is 30% of your grade, each question on the exam about 6%. This is like adding 3 points to your lowest exam question.

The speaker has a very good blog here, and a highly entertaining and interesting book you might check out.

*If you are a non-native English speaker, this will be taken into account. English grammar and spelling is very silly.

2010-09-28T13:54:00.001-05:00

Some random plots related to the exam: average score by question, percentage of you choosing that question, and grade distributions for raw scores (5 questions) and with the proposed scaling (best 4 out of 5). Click on the picture for a larger version.

More details to come as I think about this a bit more ...

PH253: Exam 1 solution

2010-09-28T12:51:00.003-05:00

Here you go. UPDATE: typo in #1 fixed - I missed a couple of primes.

PH253: HW5, misc

2010-09-24T12:05:00.000-05:00

Here is the exam you took yesterday. Your HW5 is to solve the two problems you didn't choose on the exam, due Monday before midnight. My suspicion is that a few of you get together in a group, you've probably solved them all amongst you ...

Also, I'll have your exams back on Tuesday at the start of class.

A recent tour-de-force experiment by NIST managed to demonstrate gravitational time dilation on ordinary length scales. Neat stuff. (We didn't really cover gravitational time dilation, part of general relativity, but there is a small bit on it in your textbook.)

PH253: exam formula sheet

2010-09-22T15:44:00.002-05:00

here.

PH253: random exam hints

2010-09-22T10:29:00.002-05:00

Just sent this as an email to one of you:

I think the best thing to study right now would be 1) the practice problems I put out - I will use one or two of them directly on the exam, and 2) this semester's and last semester's homework problems, focusing on the shorter problems (not the really lengthy and mathematical ones). The exam questions will be easier than most HW problems, but covering similar topics.

The book doesn't have many good problems for 2.4.1-2, I have to admit. The problems on uncertainty will be like numbers 9 & 10 on the practice problems - using a de Broglie wavelength and the uncertainty principle together, but in a more or less straightforward way. If you can do those two problems, you are more or less OK on 2.4.1-2.

For Compton scattering, just read the notes I put out, and that should be enough.

For relativity, the sample problems are good.

For the Photoelectric effect, there is really only the one equation - it will have to be something like given wavelengths and voltages, find the work function ... not much else to ask.

For photons & the quantum hypothesis, questions will be like something like the HW problem finding the number of photons per second put out by a radio transmitter.

For radiation, it will be a simple example like given an acceleration, find the power radiated by a charge, or the energy radiated in a time t (E = Pt).

Today's schedule, approximately

2010-09-22T10:02:00.000-05:00

I have meetings from about 1-3, so today is a bit less open than I had hoped. Here is when (and where) I'm likely to be available:

11-12:30 Gallalee 110
~3-5:30 Bevill 2012

I'll be reading email regularly this evening for last minute questions as well. I will try to be in Gallalee by about 10:00 tomorrow for any truly last-minute questions.

Special colloquium next week!

2010-09-21T09:49:00.000-05:00

Next week, on Thursday, 30 September at 7:30pm, we are having a very interesting public talk in 227 Gallalee:

"What Every Dog Should Know About Quantum Physics" by Dr. Chad Orzel of Union College

Chad Orzel is the author of a popular physics blog called Uncertain Principles: http://scienceblogs.com/principles/

and the author of a book titled "How to Teach Physics to Your Dog"
http://dogphysics.com/book_info.html

Chad Orzel's bio can be found here:
http://dogphysics.com/about_chad.html

Here is an abstract for Chad's public talk:

Quantum physics, the science of extremely small things like atoms and subatomic particles, is one of the best tested theories in the history of science, and also one of the most bizarre. Many of its predictions -- particles that behave like waves, cats that are alive and dead at the same time, objects that pass through barriers as if they weren't even there -- seem more like science fiction than science fact. This talk will explain the reality behind some of the stranger aspects of quantum physics, and why it is so important that even dogs should know about it.

PH253: Exam 1 practice problems

2010-09-20T23:17:00.000-05:00

Here you are. It is unlikely that there will detailed solutions before Thursday, but I will try.

Remember, the exam has 7 problems and you must do 5 of them. I will provide a formula sheet with all the necessary equations & constants (an example of which will show up tonight or tomorrow), what you put on the sheet you're allowed to bring in is up to you.

It will be important that you manage your time -- don't get stuck on any one problem too long, since you have the freedom to skip two of them. If you really don't know how to go about a problem, don't freak out: just pick another one. Choose your problems carefully, and start with the ones you think are easiest.

PH253: Exam 1 coverage

2010-09-20T11:40:00.001-05:00

Reminder: Exam 1 is this Thursday during the normal class period.

Sections of the textbook covered on Exam I:

1.2.1, 1.2.2 EM Waves
1.3 Special relativity
1.5.1-3 Appendix to special relativity
2.1.1-3, 2.1.5-6 Quantum hypothesis & radiation
2.2.1-3 Photoelectric
2.3.1-3 Photons / Compton
2.4.1, 2.4.2 de Broglie, uncertainty

Things not in the textbook on Exam I (from notes provided):

Power radiated by an accelerated charge (no derivations, just the Larmor formula)
More detailed discussion of Compton scattering

Remember that you can bring in one standard 8.5x11in sheet of paper with formulas, etc., front & back. If you write on only one side, you can bring 2 sheets. Bring a calculator.

A few more practice problems will show up this evening.

PH255: Writing a scientific paper

2010-09-20T02:06:00.003-05:00

Lab reports are a real pain, and I know many of you in PH255 have been struggling with how to go about writing a lab report. Here's how I usually go about writing a paper:

You can have about 4 figures in an average paper for a journal. Figure out how to tell the story of the experiment in pictures alone. You cannot possibly spend too much time making the figures pretty & logically consistent, look at examples from the journal (or class) you are submitting the paper to for proper style & formatting.
Describe the pictures/graphs, how you got them, and what they tell you. This is 75% of the paper.
Write the setup & procedure you followed to do the experiment, put this before the descriptions. Write down the analysis you followed afterwards. This is usually straightforward for a class project, you probably have a lab manual.
Harder, write an introduction/motivation for the experiment (including the background theory) - why did you do it, and what did you expect to find?
Write a conclusion - what did the data tell you, and how does that contrast with what you expected? Can be short.
Write an abstract/lead paragraph. This is the hard part, since most people will read your abstract first and *then* decide whether to read your paper.
Hardest, come up with a catchy title. No one will read your abstract, much less your paper, unless you catch their eye first.
Make sure you properly acknowledged your funding agents and included as co-authors everyone who performed significant work. Being highly political, leave this to a senior project member if possible ;-)

Anyway, that's what I tell my grad students, and what I follow myself by and large, and it seems to work well enough. Sort of an inverted pyramid - start with the trivial things you can describe easily, and work your way up to the crucial aspects everyone will notice first once you've figured out everything else. Scientific writing isn't much different than any other writing. You have to know your audience, capture the reader's interest, and tell your story in an efficient and compelling fashion.

PH253: HW4 solutions

2010-09-20T00:36:00.002-05:00

Here you are.

Interference & diffraction

2010-09-17T15:42:00.002-05:00

http://www.flickr.com/photos/animal-mafia/161879717/lightbox/

It's funny 'cause it's true

2010-09-16T20:16:00.000-05:00

http://xkcd.com/793/

PH253: EXAM 1 DATE MOVED

2010-09-16T12:31:00.002-05:00

Exam 1 has been moved to THURSDAY. It is not on Tuesday. Full stop.

PH253: HW4 hints

2010-09-15T20:59:00.001-05:00

I'll be updating these through the evening as I finish them up. The link will be persistent. I'll post here when they are complete.

UPDATE: barring any typos I find later, the hints are about as complete as they are going to get.

PH253: HW4 typo

2010-09-15T09:48:00.000-05:00

Fixed a typo on number 2; both uncertainty relationships should be > h/4pi, not > 4pi. Same link as before.

Black body radiation & climate change

2010-09-13T12:16:00.002-05:00

Interesting interview/discussion on how black body radiation provides feedback for earth's climate.

PH253: HW3 solutions

2010-09-13T00:53:00.002-05:00

HW3 solutions are out. Enjoy.

PH253: HW4 is out

2010-09-12T22:22:00.001-05:00

Here you are. As usual, we will do a number of them in class. A couple of quick notes in advance of more substantial hints:

For number 3, you will need to look up the intensity pattern for single-slit diffraction. Presume the electron must be confined within the central, most intense region, which gives you an estimate of position uncertainty.
I've asked number 6 before.
Number 7 is a famous thought experiment, it can be found in the wikipedia article on the uncertainty principle.
Number 8 is a straight math problem (math we'll need soon). Don't let the the unfamiliar terms stump you, all you need to do is integration and algebra for parts a-c.

UPDATE: fixed a few typos, in particular on number 8.

PH253: Textbook

2010-09-10T11:28:00.000-05:00

I loaned my textbook to someone until theirs came in. If your copy has come in, it would be nice to have my book back soon ... a colleague is asking to borrow it.

Double slit applet

2010-09-09T16:35:00.005-05:00

A nice applet to illustrate the crazy double slit stuff we talked about today. You can use photons, electrons, neutrons, and helium atoms, and even use multiple sources or vary the incident wavelength. Note the different modes - high intensity, single particles, and lasers. If you like, add a detector on one or both of the slits and watch the interference go away ... neat stuff.

Also, the actual experiment with single electrons!

How to read science papers without reading every word

2010-09-09T09:47:00.000-05:00

Nice read. Applies equally well to sections of a textbook, I think.

PH253: Compton scattering notes

2010-09-09T00:56:00.001-05:00

Here are some notes on Compton scattering. And by 'notes' I really mean deriving the Compton equation, the photon and electron energies, etc., and not so much on the discursive side. They have not been heavily proofread yet, but I believe everything is substantially correct.

Consider this your mathematical guide for Compton scattering (chock full of goodies related to the homework), with your textbook filling in the basic background.

I would like to be able to keep up with notes on the same level as the blackbody notes for every topic, but it is unrealistic to do on the fly ... I'll provide what I can.

PH253: HW3 hints

2010-09-08T20:47:00.001-05:00

I'm starting a file of HW3 hints. Right now, there are hints for the first three problems, I will be updating it tonight and tomorrow to add more. Probably by class time tomorrow it will be as complete as it's going to get ... the URL will not change as I update the file. If you like, check here to look at the time stamp and see if it has been updated since you lacked looked.

UPDATE: the hints are probably about as complete as they are going to get. A little something for each of the 9 problems.

PH253: partial HW2 solutions

2010-09-08T01:08:00.001-05:00

I've got solutions to problems 1-5. Hope to have problems 6 & 7 finished tomorrow. Let me know if you find any typos or places that need clarification.

UPDATE: there is a solution for problem 6 now. Only problem 7 remains, I will try to get a solution out Wed.

PH253: HW3 is out

2010-09-07T01:30:00.000-05:00

Shorter than the last two, I think. I asked a couple of these on HW last year, and we will cover a few of them almost directly in lecture.

We should cover the bulk of the material on Compton scattering and the photoelectric effect on Tuesday, on Thursday we'll go over any remaining questions you might have.

PH253: radiation notes

2010-09-03T11:44:00.002-05:00

I've fixed sum typos in various places, the latest version is at the same url.

PH253: homework deadline extended

2010-09-02T13:01:00.000-05:00

You can turn in HW2 any time up until this coming Tuesday's class, 11am on 7 Sept 2010. I'll be posting more hints over the weekend, and will be around Bevill this afternoon and tomorrow afternoon.

(Also, some typos in the notes came up today, I'll fix them this afternoon/evening and post when it is done.)

PH253: HW 2.1

2010-09-01T16:02:00.001-05:00

For problem 1 on HW2, you'll find this interesting. (Note the 'dot' notation to signify derivatives with respect to time.)

PH253: key points from the last lecture

2010-09-01T13:57:00.000-05:00

The last lecture covered a lot of ground, but in the end there are really only two main things to take away from the last lecture:

1) Accelerating charges radiate electromagnetic energy (a.k.a., light). The total radiated power P in terms of the acceleration a for a charge q is

P = \frac{q^2a^2}{6\pi\epsilon_o c^3}

This is only valid for velocities small compared to c - even though we correctly transformed the field according to relativity, we used the classical expression for acceleration. This expression is known as the Larmor formula.

2) Since accelerating charges are radiating and therefore losing energy, they also experience a 'radiation reaction' force or a recoil due to the emission of radiation. This force is analogous to viscous drag or friction, and is given by

F = \frac{q^2}{6\pi\epsilon_o c^3}\frac{d^3x}{dt^3} = \frac{q^2}{6\pi\epsilon_o c^3}\frac{da}{dt}

Again, this is valid for low speeds compared to c, and is typically called the Abraham-Lorentz force. This force is unusual in many respects - for one, it represents the charge effectively acting on itself, and it depends on the rate of change of acceleration or the third derivative of position.

PH253 facebook group

2010-08-31T09:09:00.002-05:00

Find each other and commiserate. ;-)

Supplemental texts

2010-08-31T09:04:00.001-05:00

In case you're wanting to review your E&M or mechanics ...

Serway & Jewett, "Physics for Scientists & Engineers" Vol 2 (the PH105/106 book). Covers mechanics and E&M
The Feynman Lectures on Physics (in the library or the physics student lounge on 1st floor). Three volumes, covers mechanics, E&M, and modern physics. I draw on these heavily in preparing lectures.
E.M. Purcell "Electricity and Magnetism" (should be in library; uses different units!). E&M only, but it has fantastic treatments of moving charges and radiation. The only downside is the use of cgs units, which are almost certainly unfamiliar to you, and which make the formulas look a little different.

Feynman & Purcell are more mathematically sophisticated than Serway, both very casually use of vector calculus. For the most part, though, you should be able to follow the essential points even if you haven't seen some bits of the math.

PH253: applet for tomorrow's lecture

2010-08-31T00:56:00.000-05:00

http://webphysics.davidson.edu/applets/retard/Retard_FEL.html

Lets you visualize the field from moving & accelerating charges. Drag the velocity slider to start & stop a charge in an inertial frame (what we'll start with) or set it in simple harmonic motion (SHO, what we'll end with).

Society of Physics Students (SPS) meeting this wed

2010-08-30T23:48:00.000-05:00

Passing on a note from the physics student society ... it isn't just for physics majors, but anyone interested in physics.

The Society of Physics Students will be meeting in the SPS room (109 Gallalee) Wednesday at 5:30 PM. Pizza and drinks will be provided.

The plan is for this first meeting to be a 'meet and greet' of sorts, to let those that haven't been involved with SPS in the past learn what it is we do, the benefits of joining the national organization, and how to do so.

Immediately following this we'll have time to study and work on homework together, so if there's a physics problem that's had you stumped for a while, bring it in and chances are someone will have figured it out before and we can help you.

Hope to see you there,

Heath Gurganus
President, UA Society of Physics Students

PH253: homework 2 hints

2010-08-30T23:42:00.000-05:00

Check it. As will be our habit, we'll fully work some of the problems in class, and at least set up the rest. This homework is mathematically challenging in a few places, but I'll try to spend a little extra time on the most difficult spots

(Also, notice that in the notes on radiation I've included some example problems toward the end ...)

Tomorrow, we'll deal with accelerating charges and figure out where radiation comes from. In the notes I've written up, we'll start with 1.2.2 (Charges that start and stop) and try to get as far as the equation of motion for oscillating charges (1.3.5). Thursday, we'll continue from where we left off and finish off the rest.

Again, I will probably skip some of the details in the notes to focus on the most important results. I tried to be as thorough as possible in the notes so you could see how everything we need can be derived from what we already saw in PH105 and PH106.

PH253: HW1 solutions

2010-08-29T22:30:00.001-05:00

are out now. I solved several of them using the template to give you an idea of what I intend by the template. Let me know if you find any mistakes or need clarification on something.

PH253: a word on homework

2010-08-28T00:05:00.000-05:00

So maybe you didn't quite finish homework 1. That's OK, turn in what you've got and it is better than a zero. So long as you're following the material, you will be fine. Keep in mind homework in total is only worth 10% of your grade, and I drop one problem set. There will be about 10 problem sets in total, so missing one whole set makes each of the others worth (1/9)*10%~1.1% of your grade. Missing (say) 2 problems out of 10 is only 20% of 1.1%, which is practically nothing.

In other words, no big deal to miss a homework set or parts of one here and there if you've got other things pressing or just don't get a few problems. The main thing is to understand the material and work the problems out/read the solutions when you get some time, because similar things will show up on the exams ... which are worth quite a bit more. HW is mainly for practice and learning, the numerical consequences for your grade are minor.

PH253: HW2 is out.

2010-08-27T22:43:00.000-05:00

I know you're excited. We'll set up all of these in class to get you started.

Tables of integrals

2010-08-27T13:33:00.002-05:00

http://www.integral-table.com/
http://en.wikipedia.org/wiki/Lists_of_integrals

PH253: what is the speed of gravity?

2010-08-26T10:08:00.002-05:00

PH253: slides for the next few lectures

2010-08-26T02:26:00.000-05:00

For the next ~3 lectures, here are some slides I might use related to the fields of charges in motion and radiation from accelerated charges.

I say 'might' because I might decide to just draw on the board instead of messing with the projector. In any case, the PDF contains useful figures to go along with the lectures.

PH253: HW1, redux; notes on radiation

2010-08-26T01:45:00.001-05:00

First, I've heavily updated the notes on radiation, the current version has the same URL. We'll start off by considering the E and B fields for observers in motion relative to the source, and work our way up to accelerating charges and radiation. Again, not all the sections in the notes will be covered (those with a * are considered optional), I was just trying to be thorough.*

Second, I realized I forgot to give any hints on HW1 problems 5b,c and 10. I'll leave some time tomorrow for going over 5b,c and other questions you have, and 10 we will do in the course of the lecture. Note that for 5b velocity is the integral of acceleration through time. Set that up and realize it is separable (manipulate the du and dt's like fractions), and Wolfram knows the integral. For 5c, integrate once more, position is the integral of velocity through time. Problem 10 we're going to do in class as part of Thursday's lecture.

* The main idea is: relativity -> field of a charge in motion -> charges that start or stop -> accelerating charges -> radiated power. Then, power -> radiation reaction force -> harmonic oscillating charge with damping and driving field -> radiation power of a charge exposed to a driving field. Last, relate radiated power to the energy density of the thermally-generated field oscillating charges bathe at temperature T in to get Rayleigh-Jeans, and add Planck's hypotheses to fix it. It will all make sense in time ...

PH253: notes for the next few lectures

2010-08-25T02:40:00.000-05:00

Over the next three lectures, we'll be discussing radiation (light emission) in detail, and in particular the spectrum of light emitted from hot objects ("blackbody radiation"). What we'll find is that the classical description is severely lacking, and this will lead us to the necessary development of quantum physics.

I find the textbook derivations of blackbody radiation mostly obtuse, too rooted in esoteric historical baggage, and unnecessarily difficult. All this annoyed me enough to come up with some notes on radiation that will make up the bulk of the next three lectures. The notes are not quite complete yet (close, probably 'done' by Thursday), and there are a few extra bits included beyond what we'll probably cover in class.

So, 1) don't be scared by the length of the notes, you're not responsible for all of it, 2) they are long because I purposely tried to only use PH105-106 material and relativity, 3) the gain in clarity will be worth the extra time in the end, and 4) I will spell out what material you are responsible for knowing on the exam, and it will mostly be what is in the textbook. The extra derivations are mostly just for clarity, you'll be responsible for the end result.

Anyway, here's the basic plan for the next few lectures.
We know from PH106 that accelerating charges emit electromagnetic radiation, i.e., light. We want to figure out how accelerating charges emit radiation in general, and specifically find the spectrum of radiation emitted from a hot object. Why should hot objects emit radiation? In short, individual charges in atoms acquire random thermal energy, which causes them to oscillate, which means they are accelerating, which means they radiate. We aim to calculate the spectrum of radiation emitted, within a simple toy model:

Figure out how E and B transform when you change reference frames.
Figure out the field from moving charges, particularly those that undergo acceleration.
Find the radiation emitted from accelerating charges, particularly for simple harmonic motion.
From the power corresponding to this radiation of energy, and find the radiation reaction force that must be present
Use this force to compute the equation of motion and energy of oscillating, radiating charges.
Model a hot object as a collection of charges randomly oscillating due to their random thermal energy.
Realize the result is silly, and resort to Planck’s quantum hypothesis . . .

It sounds like a lot, but we will really need nothing more than introductory electrodynamics (PH106) and a good knowledge of the harmonic oscillator (PH105). When we're done, we'll have exactly the same results as the textbook for blackbody radiation, but by (hopefully) a much more transparent path.

If that doesn't convince you, by deriving things now in the most general way possible, we'll get to re-use all this hard work later in the semester. Hopefully, by the time we are done with the semester, everything will tie together nicely ...

Just neat.

2010-08-24T02:09:00.002-05:00

By the end of PH253, you should have a good idea of how this works. I hope.

PH253: Lecture 2

2010-08-24T02:06:00.000-05:00

Tuesday's lecture will cover the following:

Lorentz transformations (relating position, velocity, and time in different frames)
Space-time diagrams
Momentum
Energy
Force

Last year's scanned notes are here, by the way.

What we'll cover this week is a combination of the PH102 notes linked in the last post and most of what I have in the scanned notes entitled "relativity_L3.pdf." That corresponds to sections 1.3 and 1.5 in your textbook for Tuesday, on Thursday we'll (probably) spend most of the time applying relativity to what we already know of E&M. You can read either the textbook or the notes I'm linking, whatever you find more enlightening ...

PH253: HW1 hints

2010-08-24T01:58:00.000-05:00

Tuesday, we'll set up most of the homework problems, time permitting. Thursday, we'll set up the remaining problems. Until then, below the fold are some hints on how to get started. I would agree that this HW is conceptually difficult, and requires a good knowledge of calculus in some spots. Later HW sets will be less conceptually challenging, but the math will not let up, sadly.

Also, keep in mind I may have asked some of the same problems last semester, if you dig around the HW directory ... you may also try ph102.blogspot.com. Questions I've asked before, somewhere, sometime, have a * next to them below.

Lastly, the PH102 notes I posted previously will be enough to get you through Tuesday's and Thursday's lectures. Though some of the derivations are missing, the basic results are there. For Thursday's lecture, check out the beginning of the chapter called "Magnetism" for a derivation of B from E.

1*) This is a classic paradox, worthy of its own Wikipedia page. The observer in the barn sees the doors close simultaneously, but the pole contracted. The observer with the pole sees the barn length contracted, but the doors don’t close simultaneously ...

2) a: basic mechanics
b: in one direction, you have to add velocities, and in the other subtract
c: add velocities as vectors. If the pilot wants to go straight, he or she must make the plane’s velocity point into the wind a bit, the net forward progress made is determined by adding the wind and plane’s velocities as vectors. The plane's airspeed is the hypotenuse ...

3*) The length is shorter by &gamma ; the time is longer by &gamma

4*) Small typo in the original problem set, now fixed. Use the Lorentz transformations to relate u and u’ and t and t’, take derivatives of each relationship and divide.

5*) Force in relativity is still dp/dt, but note that p = &gamma mv. Thus,

F = \gamma m \frac{dv}{dt} + mv\frac{d\gamma}{dt}

Find d&gamma/dt in terms of v and dv/dt. Set F=qE and solve for dv/dt=a

6) I should have specified that the particle is moving perpendicular to the magnetic field to make things more clear. From PH106, you know F=qvB, and you know that a particle moving perpendicular to a magnetic field obeys uniform circular motion. From #5, you know how to write F using relativity. In uniform circular motion, the speed |v| is constant, so d&gamma/dt is constant since it only depends on v² (dv/dt is not constant though). Thus, &gamma(m)(dv/dt) = qvB. You want &omega=v/r.

7) The energy of photon is hf = hc/&lambda, we’ll get to this. Use that, watch the units (nm=1e-9), and that's about it.

8*) The length along x is contracted, but the length along y is not.

9*) The x velocity in the new frame ux’ is given by the velocity addition formula. The y velocity we’ll derive in class, but note that

u_y^{\prime} = \frac{dy^\prime}{dt^{\prime}} = \frac{dy^\prime/dt}{dt^\prime/dt}

The numerator is the same as uy=dy/dt, since there is no length contraction along y, and the denominator you can find from the Lorentz transformation between t and t’. The speed is found from the components ux’ and uy’ as usual.

10) We’ll do this in class on Thursday. Think about the dimensions of the capacitor and how they may or may not be contracted. Charge is invariant, it is the same in all reference frames. How does the field between the plates depend on the charge *per unit area* on the plates, and what is that for each observer? One field remains the same, the other is a factor &gamma larger for the moving observer.

Lecture notes for relativity

2010-08-19T00:01:00.000-05:00

We'll be starting out with relativity for the first 2-3 classes (Ch. 1 of your text), and you might find some notes I wrote [23Mb PDF] useful as a supplement. The first chapter of the notes covers relativity; the rest should be review, but might still be helpful. The notes are for PH102, but that class actually covers relativity in about the same way (albeit a little less 'mathy').

Also the slides I'll use for Tuesday's first lecture are here.

Link: modern physics lecture notes

2010-08-18T09:16:00.002-05:00

There are some nice online lecture notes for a comparable course here.

PH253: Course schedule

2010-08-16T00:39:00.000-05:00

Your course schedule, as a simple spreadsheet, or a Google calendar.

Note before booking any travel arrangements that we have that extra-awesome 8am Friday Dec. 10 final exam slot.