Exam Grades

Your exam grades (as well as other updated grades) are available on Moodle now. The overall grade has already dropped one homework, one quiz, and one lab.

The exam results were mixed. On one hand, the average (70.8%) was not that bad, nor was the standard deviation (10.6), but the distribution shows a strong tail to the left:


I will probably end up scaling the exam upward by about 5 points, I will decide after more detailed analysis and let you know later this week. No one got 100%; 18/20 was the maximum score.

There is one prevailing theory to explain the average being a bit lower than expected, given that I thought the exam was far easier than the homework sets. Below is a scatter plot of homework scores (x axis) versus overall grade (y axis). There is a mind-bogglingly strong correlation between overall grades and aggregate homework scores.


So. If you do the homework, statistically there is a strong tendency for you do well in the class. Part of this is due to my tendency to reuse questions (in spirit, if not precisely). Part of this, however, is the fact that the homework assignments are constructed to get you thinking (and reading!) about the most important topics. It is not busywork ... I promise that if you grind through the homework, it will pay off. If you find yourself having trouble with the homework, you can always email me or drop by my office.

Anyway ... two main points: (1) the test will be scaled a bit, and (2) the homework really is worth your time, as much as it sucks.

Solution to today's ciruit exercises

Here you go. Includes an example of how to use Cramer's rule ...

Exam I solution

Here you go. You should get them back on Wednesday.

Today's exercise

Some problems on circuits. Practice makes perfect.

Wednesday we'll go about wiring up some more complicated and useful circuits.

Platonic solids made of resistors

You can look, but be sure to write down your own solution in your own words.

Sample formula sheet / Exam 1

Just heard on TV:

"It seems like you need to be a physics professor to buy a TV."

... this is not true. It does not really help. I was as bewildered as anyone else last time I bought one. Most of the complexity arises from marketing and intentionally vague specifications, not physics ...

Anyway: sample formula sheet. Something like this will be attached to the exam. Thus, anything you see on this example sheet you do not need to write on your own.

Recall: you are allowed to bring one sheet of 8.5x11in paper to the exam, with whatever you like on it. You will need a calculator as well; cell phones acting as calculators is strongly discouraged.

Lab procedure 24 Sept 08

Here you go, we will verify the rules for adding resistors in series and parallel.

Sample exam 1 questions ...

... are here. As you can see, they are based on problems you have already seen, and the actual exam will look similar to these questions.

On the real exam, there will be 15-18 questions.

I will put out a key for these soon, and probably add a few more (there should be more on Gauss' law, certainly).

Quiz, Exercise, and Homework solutions

Excepting the java applets we did, the solutions to all exercises, quizzes, and homework sets are now up. The easiest thing to do is start here and root around a bit. I tried to make the naming and hierarchy as obvious as possible.

I will try to update Moodle tomorrow so all of your grades to date are online, and will also try to post some example exam questions. I realize you have no good reason to believe me thus far, but the exam questions will really not be that bad ;-)

Finally, note the syllabus here, which tells you how much everything is worth.

Today's exercise

Current and resistance. Print one per group, you can put all group members' names on it.

Happy Birthday to Michael Faraday

Woot.

Checking grades online

I how have a system set up so you can log in and see your grades.

1) go here: http://faculty.mint.ua.edu/~pleclair/moodle/

2) Click on "Physics 106-4, Fall 2008."

3) Then, to log in to the system:

• your username is the first letter of your first name + your last name.

• Thus, if your name is "Jebediah Dingus" your username is "jdingus" ...
  

• your password is the last four digits of your CWID. You can change the password if you like after logging in.

Once you have logged in successfully, you should be at the main ph106 course page. There are a great number of things on this page, most of them are not useful. This is a new (and free) online course system I'm test-driving, so most things are just placeholders.

From this 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.

Any feedback you have on this system is helpful. Let me know if it works ... and I should have more grades entered early next week. Right now, only the first three quizzes and homework grades are there.

Homework 5 is out

Shorter homework, given the exam on Friday.

EDIT: In a moment of weakness, I have made HW5 due on Wed, 1 Oct. That is, next Wednesday, rather than this coming Friday.

HW4 solutions

Here you go.

Please read the homework solutions. They will be of great utility in studying for your exam this week, and they cost me a lot of time to produce.

McNair Scholars program

Just got the following I thought I'd pass along ...

We are currently accepting applications for the 2009 cohort of McNair Scholars. The deadline for submission of applications and recommendation letters is Friday, Nov. 7. More information is available at the McNair website, from Program Manager Dr. Nancy Campbell, or the Program Assistant Stephanie Hicks. Applications and forms for recommendations may be downloaded from the website or picked up at the office, 326 Osband. Eligibility criteria include: U.S. citizen or permanent resident; junior class standing by summer 2009; GPA of 3.0 or higher; potential for doctoral study; and either (a) first-generation college student with a qualifying income or (b) member of a group underrepresented in graduate study. McNair Scholars is a TRIO program of the U. S. Department of Education.

Foo!

Problem 1.7 is really interesting.

Exercise III solution

Here is the solution to the exercise we did on Monday. It is worth a read, I think, even if you solved all of them correctly - I added a few things here and there

Today

Today I'll be in my Bevill office (228) from about 10:45 onward, feel free to drop by.

I'll try to leave a note on my door if I duck into one of the nearby labs, you can also call my cell if I you don't find me there.

Image charges and conducting plates

Foo. Bar. Biz. Baz.

Tomorrow's Lab (17 Sept. 08)

Tomorrow, we'll investigate capacitors. Here's the procedure.

UPDATE: Alternate link, in case the symbols do not show up properly.

Yesterday's exercise / extra credit

Just a reminder: the fourth problem from yesterday's exercise (see previous post) is extra credit, worth 1/10 of a homework set. Bring it on Wednesday or email it to me.

As super-double-extra-credit, worth an additional 1/10 of a homework set, show that integrating the surface charge density over the whole plate gives you -q. I suggest once you find the density as a function of lateral position on the plate, integrating the area in polar coordinates, over r(dr)(dtheta), where r would be the distance along the plate.

Also, I'll be around my Bevill office until about 1:30 today if you have homework or other questions. Feel free to drop by.

Exercise for today

Today, in lieu of a laboratory, we'll work out some problems related to today's lecture.

Find them here; print one per group, turn in one per group.

Homework 4 is out

Here it is. I think it is easier than last week's ... there is definitely less math involved. Still, you would be clever to start on it early in the week.

Useful course notes

First, your reading for the next week is Ch. 26 in Serway, capacitance and so forth.

Second, here are some useful notes from an E&M course at MIT that are pretty well done. The mathematical level is roughly on par with what we have been doing, perhaps slightly higher in some places.

Third, I think I already mentioned this, but you might find my ph102 notes useful for separating the physical understanding from the mathematics.

Fourth, another random set of notes. This one is again from MIT (they are good about putting things online), but the mathematical level is somewhat above what we have been doing. If you bought the supplemental text, or have already had Calculus III, these might be worth reading through. Beware, these notes use a different set of units than we do! In the cgs units, Coulomb's constant is set to 1, and it will be missing from many otherwise familiar formulas.

Finally: expect HW4 to show up in the next hour or two. I got distracted yesterday by the brutal beatdown we inflicted on WKU and didn't quite finish it yet ... as a rule I try not to post HW until I have solved all the problems myself.

Homework 3 solutions

They are rather lengthy, so don't feel bad skimming over the problems you knew how to do. In particular I showed 3 different ways to do the first two problems, to try and give you a feeling for different ways to approach problems. There is always more than one way ...

Homework 4, on capacitance, will be out later today or tomorrow morning.

Today's recitation

Today (technically, since it is the very early morning) we will spend about half our time on the first two homework problems, so don't panic if you are having trouble with those two.

You may find this link useful for the second problem. Think about what effective area the pressure acts over to pull the hemispheres apart ...

Friday's recitation and quiz

Tomorrow, we will spend the first half hour or so going over only homework problems 1 and 2. More specifically, I'll show you 3 different ways to solve both of them.

After that ... the quiz. Read Ch. 25 and you'll be just fine for that.

By the way ... the recent poll had Friday as the preferred homework due date by an 8:1 margin. Thus, we will keep Friday as Homework Day.

Wednesday's lab

Here is the procedure. This one is not too difficult, and usually works out very well.

Please read through the procedure briefly before class, and make sure you have read Ch. 25 before tomorrow's class.

Homework 2 / Quiz 2 solutions

Here you go. I just finished writing them up, and will need to double-check and proofread them a bit more tonight. If you find any errors, let me know.

Quiz 2 and its solution are also online.

Wednesday's class / office hours

Tomorrow afternoon, I should be free most of the day from 1pm onward. Feel free to drop by my Bevill office (rm 228) any time after 1pm.

If you do not find me there, but my door is open, this means I stepped down to my lab for a little while, Bevill 180.

Wednesday we will not introduce much new material, but will mainly go over simpler, concrete examples of the fairly theoretical stuff we went over today. So, mostly it will be solving example problems, and applying the general things I talked about today. Part of that will be solving a couple more of the homework problems, and revisiting some prior homework problems with the new tools we have at our disposal.

There will also be a lab - our first real lab - and I will post the procedure for that tonight some time. Please try and give it a quick read-through before Wednesday afternoon.

HW 3 is out ...

Homework 2 solutions should come some time tonight. Homework 3 is now out, and due one week from today.

Next week's reading / Today's recitation

Next week, we'll be covering Ch. 25, "Electric Potential." Some of this will be familiar already (I hope) since we already talked about the work and potential energy required to build various charge configurations.

Today in recitation we'll use Gauss' law to find the force on a thin sheet of charge (more useful than it sounds). From this result, next week we will derive the energy stored in the electric field, and can start to talk about capacitors and real, live circuits.

After which there is of course a quiz.

If you have not already, I again suggest reading the quick quizzes in Ch. 24 in preparation for the quiz. The quiz is solely on Gauss' law, and requires no serious calculations.

As an aside, you might notice from the reading/lecture that there are really only three easy applications of Gauss' law in the way we are studying it:

1. long linear charges
2. spherically-symmetric charges
3. flat plates of charge

Anything beyond these three is usually either a) a trivial extension of one of the above, b) hideously difficult, or c) involves a stupid symmetry trick, but is of questionable utility. We'll do some examples of a and c tomorrow ... examples falling under category b are usually best solved by other methods.

Tomorrow's quiz

Once again, the quiz will be 5 questions, multiple choice, and will require very little calculation.

It will be derived from Ch. 24 (Gauss' law); it would be particularly clever to read through the 'quick quizzes' in that chapter.

We will also go over how to tackle question 2 on the homework (that is, we will mostly just solve it in class). It turns out that this problem gives roughly the right answer for a hydrogen molecule, for completely the wrong reasons ...

Partial HW1 solutions

I should have these finished up later in the week, and a bit better proofread.

This day in nerdery ...

1803: English chemist-physicist John Dalton starts using symbols to represent the atoms of different elements.

Wednesday's class

First, we will discuss Electric Flux and Gauss' law (Ch. 24) for a while ... including a look at the current homework set.

At least the first two homework problems on the homework will require a bit of sneakiness involving Gauss' law. The third ... well ... you should already know how to go about it at least. I strongly suggest the energy minimization approach, which I will outline for you. By the end of the day, we should have covered most of Ch. 24, and you should have a good head start on the homework.

Then, we will explore what we learned about Gauss' law with some applets.

Reading for this week

In case I failed to mention it ... the reading for this week is Ch. 24 in the Serway book.

If you can, read it before class tomorrow. If not, make sure to read through it by Friday of this week ... it may make more sense after the lecture tomorrow (hopefully).

Short week, short homework

Just three little questions. And they don't even cover new material, really.

Due Friday, 5 September 2008 at 5pm.