Marks Final Notes - Electrical Measurements
This is a two part lab that consists of skill building exercises in using meters, scopes, etc. to make DC and AC measurements.
General Notes
Emphasize to TA's that they need to emphasize to students the fact that these labs are not experiments, they are skill building exercises.
I find that many if not most of the PHYS142 students have experience with circuits from high school. So the overall skill level is higher and more uniform than in 122/132.
I set out enough apparatus for each student to build their own circuits, and make their own measurements. The only to learn these skills is to do things with your own hands.
Another point of emphasis is for TAs to show students how to test meters for blow fuses and replace them, replace low batteries, etc. without doing it for the students or giving them a new meter. I show the TAs how to do these things then instruct them to teach them to individual students on the spot when these things come up in lab. I try to foster within the students a sense of independence and ability to solve their own problems.
DC Measurements Lab
This lab requires a crapload of banana cables!
Since students work in groups of three I use one of the dual 50v power supplies. Channels 1 and 2 can be set to 5V each, plus there is a 5V logic output to power a 3rd setup.
I once tried having all three partner boards powered in series from one output of the power supply, this led to many problems with unwanted interactions between circuits. Thus the parallel approach.
My intent is that for each exercise, students draw the circuit diagram and calculate expected voltage drops and current draws, get the circuit diagrams approved by the TA, then build the circuits and make the measurements.
I tried having TAs evaluate students work in the lab, thus avoiding the necessity for an out of lab assignment, but this proved to be unmanageable in practice.
Past years there were cases where students in a group all treated the lab work as individual exercises, stronger students plowed ahead and left their slower group members behind, even leaving before their partners. This year I put reminders in the wiki for students to help out their partners, and emphasized to TAs to watch out for this.
The group exercise with the light bulb is partly an attempt to force all partners in a group to finish at the same time. I omitted the diode because it was too hard to explain to students, so they just look at the lightbulb for the non-ohmic part of the lab.
This lab requires a crapload of banana cables!
Scopes Lab
This lab could probably be improved by adding in Kevin's mystery waveform generator. Have students obtain a stable trigger on 2 or 3 different waveforms, make measurements and sketches to be handed in. Each student in a group could have a different set of waveforms to ensure everyone does the exercise.
This lab requires a lot of BNC cables and BNC T adapters.
Unlike DC circuits, scopes are new to pretty much all the PHYS142 students.
I literally expect students to deduce things like how to get a 1kHz sine wave from the function generator from the labeling on the front panel.
I use T adapters to connect three scopes to the function generator in series. Use the longest cables to go from the function generator output and TTL signal to the scopes. TTL is used for triggering exercise.
During training I try to get across to the TAs why I want the students to see the various triggering modes, input coupling, etc. I am concerned that, as is the lab is too much show and tell without enough context. The hope is that students may recall some of these details later when they run into them in later labs, but this is almost certainly not the case.
As with the DC measurements lab, TAs need to watch out for stronger students working ahead of their partners.
This lab requires a lot of BNC cables and BNC T adapters.