Physics 8c -- SPRING 2009

Course Description

9 units (4-0-5)

Second term of experiments in introductory electricity and magnetism using a take-home lab kit.

Spring 2009
in charge: David Politzer (politzer at theory.caltech)

Richard Norte (norte at caltech)
Isaac Kim (ikim at caltech)
Brett Teeple (teeps at caltech)

Essential Parts Update:

There are updated and improved parts that some of you will need this term, AND there are parts that ALL of you will need to complete your experiments. Click here to find out more.

COURSE SCHEDULE:

Experiments 9 through 12 are two week endeavors. However, the tasks are clearly divided into separate weeks in ZAP!, and you should turn in your lab book each week. You'll get comments back from your TA on the first week's work. A grade of 0 to 5 will be awarded for the whole experiment after you turn in your book the second week. The first part of experiment 9 is due on Thursday, April 9. Proceeding week by week, you should complete experiment 12 on May 28. And there is a Lab Quiz -- experiment 13, that is due on June 4.

NOTE:

Some of the .html documents contain footnotes that can only be accessed by clicking on little checked boxes.

LAB 9 ADDENDUM:

Here is an annotated version of section 4 of Experiment 9 (postscript, pdf, or html). Note that the masses for the nuts given below are the results of current measurements while the numbers in the linked documents are from a different batch of nuts.

LAB 9 DATA:

In Lab 9, you'll need to know the masses of the nuts that are used to counterbalance the magnetic force between the coils. As last measured, the nut masses were:

1/4"-20: 3.15 +/- 0.05 g

#10-24: 1.35 +/- 0.03 g

The "32" and "24" in #10-32 and #10-24 refer to the number of threads per inch, which is irrelevant to the way we use them. The current nuts are actually #10-24's (and not #10-32's).

MORE ON EXP 9:

One of our very dilligent lab book graders a couple of years ago provided further comments on the error analysis task of the first week of experiment 9. I've linked them here but can't resist adding that the labs require you to define and address tasks that are only generally suggested in ZAP!. There is almost never a single, right way to proceed. Regarding the discussion in the accompanying note, the as yet unmeasured shift in the small nut that would be required to counterbalance the magnetic force torque can be estimated (i.e., using the theory) in advance, certainly to an accurracy that would allow proceeding with the fractional error analysis that this note says you can't do. Rather than be discouraged by what appears to be professorial disarray, you should be encouraged to figure things out for yourself and do something that makes sense to you.

Here is the aforementioned note: in postscript and in pdf.

AND YET MORE ON EXP 9:

I don't know of any topic that so quickly touches upon epistemological, ontological, and teleological issues (maybe those should be vocabulary questions on the Ph 1c Prac final; certainly you shouldn't graduate without knowing them!) as the discussion of errors in science. It is easy to list (and not too hard to "derive" formulae purportedly relevant to large data sets. But what it all really "means" is another issue.

Here is yet another TA's attempt at explaining all this. Is it clearer? Do you need another? Is more material to read just more confusing? That's all a matter of taste and personality. Furthermore, the posting of these discussions is no guarantee of their value or correctness.

Click for postscript or pdf.

LAB 10 ALERT:

The original ZAP! circuit diagram for exp. 10 worked fine for years. But more recently some students have had troubles (which might be due to subtle changes in the high frequency behavior of the op-amp). In the improved version, we add two capacitors. This new design is in the latest printing of ZAP!, but older versions may be missing one or both of the capacitors. The current version is here or here.

Also, some of the op-amp pin-numbering diagrams from several years ago (including those on some of the previous years' Errata Sheets) are incorrect. The diagram on page 88 of ZAP! under "Detailed Schematic" is reproduced from a manufacturer's spec sheet and shows the convention generally used. Note that the figure shows the pins as viewed from the TOP of the integrated circuit. (The last few printings of ZAP! are correct.)

LAB 11 ALERT:

In Lab 11, you will build a x50 step-up transformer. The secondary is a 500 turn inductor, included in your kit. You wind a 10 turn primary. Sometimes a power supply built according to the instructions doesn't work because of arcing at the high voltage end of the transformer. To be on the safe side, you should consider the possible design improvements suggested here from the outset.

LAB 11:

The capacitor markings are somewhat obscure. For example:

label: 1 05 M ; 470 M ; 100 M ; 56 M ; .001 M or 102 M

value: 1 microF; 470 pF; 100 pF; 56 pF; 1 nF

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