Grades

I have updated grades on MasteringPhysics, which includes exam 3 scores and your overall grades. Have a look.

Exam 3 wasn't too bad, but I did scale it a bit. After scaling up by about 6 points for everyone, the average was 78.5 with a standard deviation of 10.5. Not quite as high as the first exam, but on par with the last one.

Most of you stayed about where you were at going in to exam 3, and the grades didn't change much overall. I'm not saying everyone is going to be happy, but most of you should feel pretty good about how you did - the overall class average was a solid B, nearly a B+.

Anyway: I'm not going to post final grades on myBama just yet, not until I've reviewed everything a few more times. If your grade ended up within ~0.5 points of a grade boundary (say, 89.5), I will carefully review your grades and re-grade your final exam to make absolutely sure of your grade.

Calculating final grades is agonizing, and I hate having to break a whole semester's performance down to a single descriptor. Not my idea though, has to be done ...

Grades

Don't panic too much, I will make sure the average comes out well one way or another.

Last exam

I will scale it if necessary.

I am a bit perturbed by how difficult the exam seemed to be, since over half the questions were either from previous exams or covered in class. I think some of you know now that 'open book' does not mean 'won't study, I can just look stuff up.'


Q1 - similar problems on many previous exams, spent a lot of time in lecture on this.
Q2 - you a lab on this, examples in book
Q3 - almost identical to previous exams you had access to
Q4 - you need to multiply by volume=Ad and use E=V/d, no tricks
Q5 - directly from previous exam
Q6 - on previous exams, done in class, basically an example from the book ...
Q7 - I did this in class, exactly the same problem.
Q8 - just need mirror definitions, no tricks
Q9 - directly from previous exams
Q10 - need only the photoelectric equation for both pairs of data

Anyway, the thing is done now. I'll have it graded over the weekend at some point, and will put the grades on MasteringPhysics. I will scale it if need be, we'll just have to see how it goes.

Grade updates / last class

If you gave me lab grades that needed to be corrected, I think those should all be done now. Please check through your lab grades and see that everything makes sense. The paper grades (lab 1) are in now as well - so if you wrote a paper, make sure you got a grade ...

The only outstanding grades other than exam 3 are now the Planck's constant lab and the last HW due Wed night. We'll go over those problems in class tomorrow (Wed) so you can get them done quickly after the exam [I'm just going to go ahead and assume many of you are putting the last one off, it seems reasonable].

Tomorrow's lecture is being decided right now ... probably we will go over energy levels in atoms and solids, but one never knows what I might do at the last moment. In any case, tomorrow's lecture material will not be on the exam.

Last summer's final

UPDATE: here are answers and sketched solutions to (only) the questions relevant for tomorrow's exam.

For your studying pleasure, here is last summer's final. I can't find my key, so I'll have to do all the problems quickly before I can post the answers ... but I will post them later this evening.

Other things this evening: grade updates (including fixing lab grades you've brought to my attention), and some hints for the exam.

Tentative exam 3 coverage

This is all pending a discussion with Dr. Mazumdar so we can coordinate ... but here are the minimal sections you should worry about:

22.2,4 reactance & power in ac circuits, there is certain to be a question about filters
23.1-3, 5-9 EM waves
24 all (geometric optics, but you won't have to draw ray diagrams)
28.1-3, 6-7 quantum and atomic physics, note in particular the Bohr model

Tentatively, there will not be any questions from Ch. 29 since that is almost purely qualitative stuff.

The test will be open book & notes, the only restriction is that no internets are allowed (i.e., no phones, PDAs, laptops, etc.).

And, very important, both sections will have the exam at 4pm on Wednesday in the usual lecture room. You will have at least 2 hours for the exam, and will probably not need all of it. If, for some good reason, you cannot make it from 4-6pm (e.g., job constraints, another class, etc.) we will work out an alternate time, but please contact me as soon as possible.

There will be 10 problems out of which you must solve 8, and they will be shorter problems than the previous exams. That is, don't freak out about there being more questions than before, the questions will be much less involved than usual HW or exam problems. They will be at the level of example problems in the book, for the most part find the right formula and go. Nothing really subtle.

More details tomorrow (Tues) after Dr. Mazumdar and I discuss a bit more ...

Today's lab

We'll measure Planck's constant.

The optics HW is extended until tomorrow night.

MasteringPhysics

Yes, MasteringPhysics has been down all day. I can't really do anything about it. The HW is not due until tomorrow night in any event, and I expect the site to be up tomorrow morning.

Exam 3

Chapter 26 (Interference and Diffraction) will not be included in Exam3. Chapter 30, on nuclear physics will also not be covered.

The exam will be open book. Bring your book and any scribbled up piece of paper that you might want.

Homework problem 2

Think of a toroidal solenoid as a cylindrical solenoid wrapped back on itself. A toroid is basically a donut. If you cut it at one point and straightened it out, it would be a regular old solenoid of length l=2πr, the inductance would be L=µN^2A/l, and the energy U=(1/2)LI^2.

The figure they provide is terrible ... look at this one.

Exam 2 scores are up

Check it out on Mastering Physics.

It wasn't that bad - average of 79.3, standard deviation 8.7. I was basically happy (though all of you might not be I guess ...). Here's the distribution, the bulk of you were in the mid-C to mid-B range.

More on this during Friday's class. Above all, do not panic: we have one exam to go, and almost no one is in any sort of danger.

Labs grades were updated as well, have a look. 

Today's lab

Today, we'll do two little experiments on mirrors & snell's law, and one on lenses:

http://faculty.mint.ua.edu/~pleclair/ph102/Labs/reflection_refraction/reflection_refraction.pdf
http://faculty.mint.ua.edu/~pleclair/ph102/Labs/lenses/lenses.pdf

Even though there are three experiments, overall it is still very fast and should not take the whole period.

In other news, the tests should be graded tomorrow. I will also extend the current HW deadline since I was out, but the next one will come out tonight (due Sun).

Today

I am sorry for the last-minute notice, but there will not be a lecture today. There will be a lab at the usual time.

Lab grades

You now have many lab grades posted on Mastering Physics.

Wednesday's lab: ac circuits

Here you go.

Makeup exam questions

They are graded, and you'll get the back tomorrow. Not on Mastering yet, but hope to update that on Tues.

The 2nd exam should be graded by Thursday - I didn't get them back this evening to get started due to a mix-up, but I'll grade them as quickly as I can.

New HW out

Due Thursday at midnight, induction/ac circuits/em waves.

The next homework after that will likely be due Saturday or Sunday. 

Office move

Over the weekend, I had to move into a different office as part of some reshuffling we're doing to free up space. My new office in Gallalee is now room 323.

Old exam answers

Exam 1, summer 2009, problem 4: this was also on the summer 2008 exam 2.

Exam 2, summer 2010: only the first three problems are material related to your upcoming exam.

1. Just walk around the middle loop - that gives 12-6I=0, and determines the current in the 6Ω resistor to be 2A.

2. Use the right-hand rule to determine directions. Two of the currents give fields pointing to the lower right corner, and two of them give fields going to the lower left corner. All fields have the same magnitude (same current, same distance; watch the geometries). All but the vertical components will cancel; find those and add together. The net field is in the -y direction, and has magnitude (field of 1 wire at center)*(sin 45)*(4 wires)~5e-6T.

3. (a) into the plane. (b) set r=mv/qB equal for both particles using the known electron and proton masses. q is the same for both, and will cancel, as will B. This gives (v_e/v_p)=(m_p/m_e)~1.8e3

4. (a,b) This filter passes speech - the inductors let low frequencies through, and the capacitor shorts out any remaining high frequencies. (c) Add all inductors together, they sum to 10.26mH. The cutoff frequency is when the inductive and capacitive reactances are equal, so f=1/(2*pi*sqrt(LC))~10.6kHz

5. This is motionally-induced voltage, like the conducting bar. (a) V=Blv~2.5mV (b) Right hand rule gives the force on a positive charge toward the drivers door, so it is the positive side.

exam 2 coverage

The following sections are fair game for the exam: 19.1-8, 20.1-9, 21.1-9.

I am aware that there is no solution to summer 2010 exam 2. I will do what I can tonight.

You did not have any homework on induction (yet ...), but it is still on the exam. Check out the old hw, exams, and solved examples in the book for some practice. We will probably have time to do a few more in class tomorrow.

There is a formula sheet essentially identical to the one you will receive on the exam here.

Thursday's lab

We'll study inductance in tomorrow's lab. You'll learn how this works in tomorrow's lecture before the lab. Also, plenty of demos on induction and magnetism tomorrow.

And, good job on the transistors lab - it went better than I thought it would, and everyone's circuits worked in the end. As you can see, however, real circuits often require a little 'fiddling' to get the working, even when the paper versions look just fine ...

Exam scaling

Long story short, just taking the total points on the last exam and grading it out of 100 instead of 120 is not really fair to those who only did 5 problems (like the instructions said). Doing it any other way makes it unfair to some other groups of students.

So here's the deal. If you did only 5 problems on the exam, during Thursday's lab you can solve one more problem to add to your test. No down side here. Exactly the same rules as the exam, except you don't have a choice of problems.

If you did 6 problems, but got only 1-5 points on one problem (i.e., the token partial credit for writing down *something*), I'll let you take the makeup problem on Thursday to replace the problem you only got token points on.

If you did 6 problems, but still feel your score could be better, then you should make a specific appeal ... I might be willing to let you replace one of your problems, and I might not, depending on the situation. Probably not if you're just aiming for that A+. Probably so if you are worried about failing. So it goes. One can't be completely fair in all things, but we'll do the best we can.

Short homework on magnetism out ...

due Friday night. Should not be too bad, we'll go over many of them on Friday.

Wednesday's lab: transistors

Here is the procedure and background for Wednesday's lab. It will probably make more sense if you have read the posted notes from yesterday, but we'll go over the basics in the lab session to get you up to speed.

Exam 1 grades

I've posted exam 1 grades on Mastering Physics now. I ended up taking the total number of points you got from all problems you did, and just taking it out of 100 instead of 120.

I arrived at this procedure by first calculating your grades that way, and also separately taking the best 5 out of 6 problems. In all cases, the first method gave the same or better grade, so I opted for the second method. That gave an average class score of 81% with a standard deviation of 15%, pretty reasonable. I was also happy that choosing this method meant substantially fewer people ended with Ds and Fs on the exam.

Anyway: please check your posted scores against what is marked on your exam (and also make sure all the points add up right on the exam) so there are no errors.

Some notes on transistors

UPDATE: the figure showing the internal diode-like connections of the transistor terminals had a mistake (the b-c one was backwards), now corrected at the same link below.

I just finished a first draft of. Two of the circuits discussed (current source, night light) are what we'll build in the lab on Wednesday. I mean build, not design - you aren't responsible for anything on these notes, you'll only be responsible for building working versions of the two circuits.

These notes are rough - I just wrote them tonight and haven't done much editing yet - but you might find them useful if you want to understand a bit more how transistor circuits work. The notes are not required reading, this transistor stuff isn't on any test or homework (and just one lab), it is merely ostensibly interesting and highly practical information. If you're curious, give them a read through. I have sections to add yet (how to build an amplifier and a few other bits), and I'll update the link as that happens.

For the actual lab on Wednesday, you don't need to read all of this or really know much about transistors at all. In fact, all you need to do is build them and measure there properties, which will be detailed in a lab procedure I'll post tomorrow. So, don't freak out, the lab itself will be entirely circuit construction and measurement (current vs voltage), no theory at all (but the circuits will do cool things). These notes are only if you want to figure out a bit more why the circuits behave the way they do, how they were designed, and how you can build your own.

As usual, if you notice mistakes or think something could be clearer, let me know. I plan to reuse these notes in later classes, so you would be helping future victims students.

Today's lab: resistors & LEDs

Here you go. Relatively straightforward, should be done early.

Eating candy off of the ground

Using equations at random is like eating candy off of the ground.

Home-made circuits

Turns out, you can make conducting play-dough.

HW3 is out

All about circuits; due next Tuesday at midnight.

HW2 #7

Q1: On problem 7 (Moving a Charge) of the second homework set I keep getting this error message when I input my answer in a variety of different ways: "There is an error in your submission. Make sure you have formatted it properly."

Q2: I'm sure I have problem 7 right, but it is being marked wrong.

I've gotten these questions many times already, and in almost every case you did have the right answer. For some reason this problem is weirdly particular about the order the operations (superscript, subscript, square root) are put in.

If you definitely have the right answer, and can prove it (screen shot, copy & paste, etc), show me and I'll just go in and override your score for that question to give you full credit.

If this happens more than (roughly) 20 times, I will decide it is not worth the effort anymore and will give everyone full credit on #7 :-)

Solutions to Sum10 exam 1

Some very quick solutions to the Summer 2010 Exam 1.

Exam practice problems

Your best bet is to dig around in the exams from previous incarnations of PH102 - just about all of them have solutions too.

http://faculty.mint.ua.edu/~pleclair/ph102/Exams/

Look at the first exams for any given year, the one from Summer 2010 is probably most relevant. Old HW problems are also good, and almost all have solutions:

http://faculty.mint.ua.edu/~pleclair/ph102/Homework/

The only trick is that HW problems are usually harder than exam problems (at least in the past, when I didn't use online HW).

Exam format

I had a couple of questions about the exam format, etc., so I'm reproducing my answer here for the rest of you to see.

The test will basically be 6 problems, and you can solve any 5 of them - so you can skip the one you think is hardest. Each problem will have multiple parts, so there is plenty of chance for partial credit (even within an individual part). A good example would be this one: 

http://faculty.mint.ua.edu/~pleclair/ph102/Exams/Sum_2010/ 

(This exam from last summer had them solve 6 of 8, but that ended up a bit too long). Again, heavy partial credit if you seem to more or less know what to do, but just make some small mistakes, or just get part of it right.

The formula sheet is totally unrestricted so long as it is 1 page of normal paper on both sides, or two sheets with only 1 side of printing each. Otherwise, it can have on it whatever you like.

The other section of PH102 this summer ...

They also have a blog. Some nice links posted there. (Both sections are covering the same material on the same schedule, fyi.)

Wednesday's lab: electrical components

UPDATE: I've included another part of the experiment in which you'll learn about the function of photoresistors, and a bonus circuit construction project where you'll build an 'electric eye' circuit if you want some extra points. The files are in the same directory linked below
----------

Wednesday's lab is a simple one on components, designed to introduce current & voltage and operating the lab boxes. Find it here: http://faculty.mint.ua.edu/~pleclair/ph102/Labs/components/ (2 parts, 2 files).

One small warning, of sorts: this lab is not at all as obvious as it seems when you take into account non-idealities of components, sources, and meters. Once you've seen it once, though, it is straightforward. That is part of the point of the lab - how to real components, sources, and meters work, as opposed to the ones in the textbook.

I will probably add a small section to the lab at the end where you will explore photoresistors and LEDs combined to make a simple sensor-actuator setup, just a qualitative thing where you describe what happens. I will post the revised procedure late tonight.

Exam 1 is soon

Exam 1 is coming up on Thursday. It is rather soon, but there are reasons for this ... The exam will be held during your lab period, in the lab room. Even if you have my lecture and the 5pm lab, you still take the exam during your normal lab period. It will take you 60-90 minutes. Don't be late. Here's what it will cover, just two chapters:

• Electric Forces & Fields (Ch. 17 in the text, all sections)
• Electrical Energy & Capacitance (Ch. 18 in the text, all sections)

Note that relativity is absent.

The format of the exam will be 6 problems (i.e., solving stuff, no multiple choice), you pick any 5 to solve. Put another way, I'll give you 6 problems, you can skip any one of them you like, they are all worth the same amount. To head off an obvious question: if you do all six, I may grade all six and take the best 5 as your grade. Or, I might just grade the first 5. Who knows. Your best bet if you do all six is to tell me which 5 you want me to grade.

I will provide a formula sheet (example) with all relevant constants and basic formulas, a list which should be sufficient to solve all problems. Additionally, you are allowed to bring in a single 8.5x11 inch sheet of paper with your own notes, formulas, etc. -- anything you want, really. Front and back sides are allowed, I will allow two sheets with only a single side if you prefer that. You are additionally allowed writing implements and a calculator (i.e., not a cell phone or any network-enabled device). You can feel free to program your calculator in arbitrary ways, however, just no internet or peer-to-peer communication of any kind.

I don't know if I can stress enough that you should not forget your calculator.

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 ...

Relativity HW extended

I'll push the deadline for the relativity HW until Friday so you can worry about the test more efficiently.

This will not affect the HW2 deadline, nor the occurrence of HW3 shortly thereafter.

(This is for Dr. LeClair's section only. Dr. Mazumdar may or may not decide to do the same.)

HW2 is out

Your second homework set is out (LeClair's section), due Wednesday at midnight. It is a bit longer than the first, but meant to double as study material for Thursday's exam. More details on that later, however ... for now, suffice it to say that you should not delay in starting the second homework.

There is likely to be a shorter homework due on Friday covering current & dc circuits.

Tomorrow's lab

Tomorrow, you will measure equipotential lines. A lot like electric field lines, we'll learn about them in the lecture.

Syllabus

Course syllabus. Note that one lab and one homework grade are dropped. Repeat, one homework and one lab dropped.

Intro & relativity slides

Here are the slides from the first two lectures, which contain the intro/syllabus information and some figures for the relativity material.

MasteringPhysics

If you have not been able to register for MasteringPhysics, it is because the existing code has been used too many times. If this is the case, email me and I will give you a new code.

If you're already signed up for MasteringPhysics for my or Dipanjan's PH102 section, you don't need to do anything. This is just if you haven't been able to sign up.

Two kinds of electric charge

Two kinds of electric charge

HW1 is out

For Dr. LeClair's section: your first HW (on relativity) is out on MasteringPhysics now, due Monday at midnight. We'll go over some of the questions in class on Monday.