Gas station without pumps

2013 February 8

Fourteenth day of circuits class

Filed under: Circuits course — gasstationwithoutpumps @ 18:46
Tags: , , , ,

Today’s class started with another do-now problem: What is the voltage gain of the following circuit?

voltage-divider-virtual-ground-ampThis circuit was intended to be more of a hook than as a test of former material, though they’ve had all the tools needed to solve it.  I worked them through finding the Thévenin equivalent of the pair of 2.2kΩ resistors (which is tricky, since the equivalent voltage is 0V, and the short circuit current is also 0—the resistance needs to be determined at some other voltage).  We then plugged the circuit back together and everyone could get the right gain.

I did one more explanation, of the voltmeter symbol and how you could decompose a bridge circuit into two voltage dividers, and I turned them loose on doing quiz corrections in groups for the rest of the class time. They broke into 3 groups and I circulated around the room, answering questions and occasionally giving advice.  Every once in a while I would answer a question by going to the board and doing a 2-minute explanation, which everyone in the room watched, even those not in the group that asked the question. I’m requiring them to turn in quizzes on Monday with all the answers correct.

The students seemed to be getting into doing the quiz corrections, and a lot of good questions came up that exposed misconceptions.  I forgot to ask students to bring laptops on Monday, so I think I’ll push the gnuplot in-class work to Wednesday.  That will give me some time in the lab after class on Monday to gather some data to do another modeling project with.  On Wednesday we’ll go through building the model to explain the data.  I’m thinking of modeling the impedance of their loudspeakers as a function of frequency, as that should have some interesting modeling issues, provide clean data for fitting, and be useful to them later on when they have to design the class-D amplifier.

On Monday, we’ll probably do a bit more on the quiz corrections (if people still have questions that they are struggling with), and start on inductors, as we’ll need them for modeling loudspeakers.  I might introduce inverting amplifiers also.


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