Gas station without pumps

2015 April 24

Email exchanges with the electronics class

Filed under: Circuits course — gasstationwithoutpumps @ 08:35
Tags: , , ,
On Thu, Apr 23, 2015 at 11:07 PM, a student wrote:

The lab report being due Friday, the day after lab, makes it hard to write a good lab report to which I feel I understand the material well, and I know many other students that feel the same way.  The labs this week were confusing and the material was hard to grasp, especially with the last minute changes to the textbook and late lecture material.Most of the students were in lab an hour and half after the lab period, trying to grasp the key points of the material we learned this week. I think writing a report due the next day will cause us to brush over key concepts of the labs and write only on the material we were comfortable with. I know every week,  my classmates and I stay up all night to complete reports without truly understanding the material. As much as you would like us to write the majority of the report before the lab, the concepts start “clicking” when we are in the lab, we can reflect on why we did each part of the lab and how it relates to the theory of the course material. Please consider extending the due date of the final reports to the next Monday with pre-labs.  
​My e-mail response to the class:
The due date of the lab reports is something I spent a lot of time thinking about.  The two reasonable due dates are Friday and Monday after the Thursday lab.  (I also considered a Friday due date for Thursday-Tuesday lab pair.)
In previous years I used the Monday due date, with the expectation that this would give students lots of time to do the writing.  The results were not as good as I would have hoped.  The writing did not show that much a lot of time had been taken over the weekend, and students didn’t start reading the next lab until Monday night, coming into the Tuesday labs completely unprepared.  Lab steps that should have taken 20 minutes were taking 2 hours, because students were trying to to the reading and preparation in lab.
This year I decided to try the Friday deadline, expecting some drop in the quality of the writing, but an improvement in the efficiency of lab time.
The results (so far) have been that the lab time has been used much more efficiently (I still need to work on the design of the hysteresis oscillator lab, which was reduced from about 8 hours last year to about 4–5 hours this year, but needs to get down to 3 hours).  And the reports are not noticeably worse than previous years.  In short, the Friday deadline seems to be working better than the Monday deadline did, so I’m reluctant to change something that is working to something that had not worked.
The only suggestion I have for reducing the amount of time spent Thursday night is to take more time on the weekend creating schematics and writing the structure of the report (what you expect to do, with placeholders for the data).  This advance preparation will increase lab efficiency, reveal difficulties which you can ask about in class before lab, and make the writing not be a last-minute effort.  It is also a good general practice for writing journal papers, design reports, and other documents—do as much of the writing as possible near the beginning of a project, rather than leaving it as a “cleanup” activity at the end.
On Fri, Apr 24, 2015 at 12:14 AM, a student wrote:

I was wondering what you meant with this question for Lab Day 1:

What is the largest peak-to-peak square wave that you can apply to your loudspeaker without exceeding the RMS power limit? 
I feel like we need to have values from an oscilloscope to find the peak-to-peak square wave or am I thinking of this wrong?
​My e-mail response to the class:
The RMS power limit is a specification on the spec sheet (either 10W for the old oval speakers or 15W for the new round speakers).  The question is at what voltage you will dissipate that much power in the loudspeaker.
Some key concepts that we did not have time for yet in class:

  • RMS power is root-mean-square power.  Take the power as a function of time, square it​ (or, more correctly, square its magnitude), average that over time, and then take the square root of the mean.
  • Instantaneous power is voltage times current.
  • For this exercise, I meant for you to use only the approximation that the loudspeaker is a resistor (which is ok if you are at a frequency that puts you near the baseline of your plot).
I just realized that the section at the end of the loudspeaker chapter about power was not completed.

Because neither the book nor the lecture has covered RMS power yet, don’t worry about those questions—I don’t expect you to pick up those concepts with neither textbook nor lecture support.
I think part of the problem was that the loudspeaker lab was later in the quarter last year (week 5), so we’d had a little more time before it, and I’d covered RMS and power by then.  Also we’ve been spending more time on gnuplot and fitting—the class is doing much better on that aspect of the course this year.  I apologize for the mismatch between the material presented and the questions, and have made a note to try to fix the book over the summer to address the problem.

Every class is an experiment in pedagogy—some things work and some things don’t.  I try to learn from each mistake (and each success), so that courses get better each time. I think that this year’s applied electronics class is working better than previous ones, but there are still rough spots to smooth out.  This week is one of those rough spots—packing the loudspeaker lab and the hysteresis lab into the same week is tight (though it worked out better than last year’s schedule, where there was more time for the hysteresis lab, but students took far longer to complete it).

4 Comments »

  1. Last thoughts first:
    RMS Power? (1) Let me google that for you — http://lmgtfy.com/?q=rms+power — is a classic response and (2) I guess it really is clear that they have not had the second semester of physics yet! You have the patience of a saint.

    I really appreciate what you are doing here, with your semester teaching diary for that course. I am thinking about writing a lab manual, with a just-in-time e-book offering a very tempting alternative to getting it all in order and through our campus bookstore’s self-publishing operation. It is very helpful to see what problems to watch out for.

    Comment by CCPhysicist — 2015 April 24 @ 20:32 | Reply

    • Most of the class have had the second semester of the physics class! That doesn’t seem to help. Unfortunately, the physics department here have watered down their physics class for biologists until it is barely high-school physics (it was supposed to be calculus-based, but all the students say that there is no calculus in it—it seems to be at the level of the new AP Physics 1 and AP Physics 2, but not a very good rendition even of that). I’ve been encouraging students to take the real physics course, but the Physics Department only offers it once a year and then doesn’t provide enough seats to meet the demand. Requests that they teach it twice a year to meet demand (and provide engineering students with some flexibility in their scheduling) have fallen on deaf ears.

      Comment by gasstationwithoutpumps — 2015 April 24 @ 20:39 | Reply

      • I never would have guessed that bioengineering had trig-based physics as its required course. (Engineering schools in this area have a biomedical or biomechanical major with the same requirements as chemical engineering or biochem majors.) You are teaching a REALLY rigorous circuits class to students with that background! I wouldn’t assume they know much more than V=IR and certainly nothing about AC apart from health and safety considerations, and are pretty much still in shock from the first week.

        By the way, your comments about trig-based physics would apply to a course I was involved with decades ago as well as ones I know about today (which do seem watered down to keep the passing rate up). Even back then it barely touched on topics that we spend weeks on in the class for engineering majors, trading those for topics like radiation that pertain to pre-med requirements. Having reviewed the new AP curriculum, I think that remains true for that course. If anything, the new AP class reflects a greater shift toward more conceptual understanding and a hands-on approach in the classroom that the new MCAT exam favors. (Our chemistry sequence is being re-worked because of the changes in the new MCAT.) The main advantage of the new AP2 class is that it isn’t treated as an afterthought, either in the classroom or when testing it.

        Comment by CCPhysicist — 2015 April 25 @ 10:45 | Reply

        • We have to allow students in MCD biology to switch to the biomolecular concentration in bioengineering, and they only take the lower-level physics course. That physics course is still listed in the catalog as calculus-based, but students have told me that it is not. For the bioelectronics and assistive technology:motor concentrations, we are requiring calculus-based physics, and recommending it for all bioengineering students.

          About all I’m expecting the physics class to have taught them is V=IR and Q=CV, though it would be nice if they had seen the differential equation that leads to exponential charging and discharging of capacitors. Mainly I want them to have used calculus for something, but that seems to be too much to expect of even the students who took calculus-based physics. They all seem to have just memorized a few formulas, with no idea of when a formula was applicable. Even applying V=IR causes a number of them problems, because they don’t distinguish one voltage in the circuit from another, and seem to have trouble with the idea that the formula only applies to the voltage across the component that the current is through and the resistance is of. They’re getting better about these things, but from all I can see, most of their physics and chemistry courses have had no affect whatsoever on their ability to think about physics or chemistry.

          Comment by gasstationwithoutpumps — 2015 May 2 @ 09:04 | Reply


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