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2018 April 4

Quiz disappointment

Filed under: Circuits course — gasstationwithoutpumps @ 22:31
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Today’s quiz in class was very disappointing for me, and I don’t know what to do differently to get better results.

Yesterday in lab I returned the quizzes from before break and urged students to look through all the old quizzes and rework any questions they got wrong, reminding them that I recycle questions.

In this morning’s class, before the quiz students asked me to show them (again) how to do one of the questions on the last quiz:

Design a voltage divider implementing Vout − Vref = G(Vin − Vref ), where G can be adjusted from ≈ 0.33 to ≈ 0.67 using a 10 kΩ potentiometer. Use port symbols to connect to Vin, Vref , and Vout.

I showed them two solutions—one that I had expected and a correct, but different solution that a student had come up with.

Here are the two solutions: mine on the left and an alternative one on the right.  (There is a third solution, similar to the second one, but with the potentiometer as variable resistor on the lower leg, rather than the upper one, and the two fixed resistors swapped.)

I had already shown them my solution a week and a half ago, right after they took the quiz, and I had posted both solutions on Piazza.  I not only showed the solution, but gave them an explanation of how it worked again and answered some questions students had about it (like why the gain was expressed the way it was with Vref, and why it was even considered a gain).

Right after that I erased the board and handed out the quizzes.  One of the quiz questions was the identical question that I had just worked on the board for them.  I was resigned to this being a free point for them (just like putting their section number on the quiz is a free point, which I use to distinguish those who are absent from those who are present but get no questions right).

But 20 of the students got no points for the question and 15 got only half credit (out of a class of about 72—there were supposed to be 79, but there were 7 students absent).  So almost half the class could not retain for 5 minutes a simple circuit that they should have been able to derive in a couple of minutes and which they had seen at least 3 times already.

Help!  During the last 10 weeks I’ve gone through just about all the ways I can think of to have the students understand voltage dividers and potentiometers, and I’m obviously not getting through to 28% of them (probably more, since the absentees are likely to be in the group that can’t do the problem also).

Does anyone have any useful advice?  (Giving up on the students is not useful advice—I want them to succeed.)

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2017 April 11

Co-instructor wanted for applied electronics course

Filed under: Circuits course — gasstationwithoutpumps @ 22:04
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I am looking for someone to be a co-instructor with me for the Applied Electronics for Bioengineers course at UCSC next year (January 2018–june 2018).  There are two reasons for my wanting a co-instructor:

  • I want to train someone to take the course over from me when I retire (in about 3–4 years).  Right now, I’m the only person who has ever taught the course, and there are no other faculty at UCSC particularly interested in taking it over. My department has no other faculty who know enough electronics, and the EE and CMPE departments are having enough difficulty covering their own courses, so I need to find someone from outside our usual faculty.
  • The course is expected to grow to 100 students next year, and I can barely handle the grading load and lab supervision for 70 students this year (71–73 students last quarter, 68 students this quarter).  If I could split the grading load with another person, we would each have a large, but manageable load.  I might be able to hire undergrad graders to do the homework grading, but not the lab reports, which require good feedback on the writing.

I’ll be hiring undergraduates to help answer questions in the lab, as I’ve been doing this year, but I would want the co-instructor to be present for about half the lab sections.  I think that we’ll have 5 sections of 20 students each, so I’d do 2, then we’d do one together, then the co-instructor would do 2.  The total number of hours a week would be about 3.5 attending/giving lectures, 9.5 hours lab, 8 hours grading, for about 21 hours a week.  I don’t know what the pay would be (depends on qualifications on paper), but the pay would probably be meager by engineering standards—I’d guess it would work out to about $40/hour, though it might be more if the lab time is properly accounted for in the pay rate.

If any of my local readers are interested in the possibility of being a co-instructor, please contact me (karplus@soe.ucsc.edu).  If you know someone who might be interested, please pass on the information.

 

2017 February 27

Understanding semilog plots

Filed under: Circuits course — gasstationwithoutpumps @ 10:22
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I realized in doing the homework grading this weekend that few of the students in my electronics course had any intuitive understanding of semilog plots (that is, plots in which one axis is linear and the other logarithmic).  I had been assuming that providing the following plot

Forward voltage as a function of current for a 1N914BTR diode.

Forward voltage as a function of current for a 1N914BTR diode.

would let students see that the voltage grows approximately with the logarithm of the current, and that means that a voltage difference corresponds to a current ratio. Very few students got that from the picture, the formulas, or the description in the text. They almost all wanted to pretend that the diode was a linear device with voltage proportional to current (i.e., that it was a resistor), so that a 6% change in current would result in a 6% change in voltage.  The whole point of using the diode was to introduce the exponential non-linearity, so this confusion definitely needs to be cleared up.

I was going to try to explain semilog plots and exponential/logarithmic relationships in class today, but my cold has gotten so bad that I had to cancel class today. That means I have another 2 days to figure out how to explain the concepts. If any of my readers can think of ways to get students to interpret semilog plots correctly, please let me know. I think that the relationships are too obvious to me for me to help students past their misunderstandings—I can’t get far enough into their mindsets to lead them out of confusion.

2016 November 3

Writing feedback

Filed under: Uncategorized — gasstationwithoutpumps @ 09:15
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In his post Omics! Omics!: 10 Years of Omicing!, which reflects on the influences on his writing, Keith Robison says

The other person who deserves nearly infinite credit for making me think about my word choices is my father.  Sometimes he strays into being a pedant and enforcing rules which have fallen by the wayside, but he did make me think when I spoke and wrote.  I’ve seen some guidelines for helping students that counsel picking only a few major errors to mark, for fear of scarring the psyche of young writers.  Dad didn’t subscribe to that viewpoint in the least, and I’m the better for it.  In high school I treasured getting back a draft with red ink all over it; it’s a service I missed in college and beyond.  That meant he had read it and thought about it, and my work was always better for it.

I think that this attitude is one that we need to see more of, both among students and among faculty. I put a lot of time into trying to provide thorough feedback on student writing, even though I know that it is not always appreciated.  I also know a number of faculty who bemoan the low quality of student writing, but spend almost no time giving detailed feedback so that the students can improve.

There are times for triage—concentrating on the students whose work could benefit most from editing, while providing only minimal feedback to those who produce word salad or whose writing is very good—but I prefer to try to provide similar amounts of feedback for all students.  For the word-salad students, my comments are mainly on sentence structure and paragraph structure, to try to have their writing make sense at least at a local level. The students in the middle get a mixture of different comments from punctuation to overall structure of the paper, while the top students get mainly get comments on trivial little details that can polish their already good writing.

2016 September 20

Trick for encouraging cooperation

Filed under: Uncategorized — gasstationwithoutpumps @ 15:26
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Adam Grant, a professor at the Wharton School of the University of Pennsylvania, provided an interesting technique for encouraging cooperation in his business-school classes (a culture noted for cut-throat competition between students):

How could I get students to help one another?

Four years ago, I found a way. The most difficult section of my final exam was multiple choice. I told the students that they could pick the one question about which they were most unsure, and write down the name of a classmate who might know the answer — the equivalent of a lifeline on the game show “Who Wants to Be a Millionaire?” If the classmate got it right, they would both earn the points.

Essentially, I was trying to build a collaborative culture with a reward system where one person’s success benefited someone else. It was a small offering — two points on a 120-point exam — but it made a big difference. More students started studying together in small groups, then the groups started pooling their knowledge.

You can read more about his attempts to encourage student cooperation in Why We Should Stop Grading Students on a Curve, published in the New York Times.

I don’t think I can use this exact technique, as none of the courses I teach involve exams—all are graded on the written reports that students write.  I could use it for homework, I suppose, but the overhead of checking other student’s responses might increase the turnaround time for homework grading.  I’m also already seeing more cooperation on the homework than I really want.

Furthermore, students quickly learn who the best student in the class is, and would just point to him or her, with no increase in useful cooperation.  So I think this technique would only work in student cultures that currently have a high degree of secretiveness and competition, not in already collaborative cultures.

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