Wednesday, July 20, 2011

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.

Tuesday, July 19, 2011

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.

Monday, July 18, 2011

Today's lab: resistors & LEDs

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