Student "edition" found at {csi dot journalspace dot com}.

Maybe I shouldn't have started this blog now, not with everything that's been going on.

In the first meeting of my Introduction to Electricity and Magnetism lecture class for the eleventh week of the first term, we finally discussed the loop and node rules of relatively complicated circuits that we had already taken up in the lab. This time, at least everyone was listening and not just the people who had to write in the lab notebook or had to write the individual reports for the experiment.

First I identified the nodes, where three or more wires meet in a circuit.

Then I defined that the individual branch currents are seen from node to node.

I stated that they now had to set the arbitrary direction of each current, to be able to come up with the equations using the node rule.

Then we had the method for identifying the loops for the voltage rule, using the nodes and some of the points labeled between the nodes.

One of the students (from the minority who transferred from another technical school and degree program) perceptively asked if the loops had to cover as much of the circuit as possible. It turns out: all the parts of the circuit have to be represented in equations numbering more than the number of unknowns to be able to solve it correctly.

In retrospect, maybe it was wrong to start with six unknown currents and six equations as the first example. I did make up for it (however belatedly) by giving them an exercise with just two nodes, three loops total and three unknown currents, that they had to solve by group.

Next meeting I will give them examples that combine both series and parallel resistors and several voltage sources, just to see that they understand the procedures.

In the laboratory class afterwards, we started with the second to the last experiment, about making galvanometers into ammeters and voltmeters of different ranges. But more on that in the next post.

Session 1239 encountered loops for the first time. Class dismissed.