## Wednesday, November 11, 2015

### Classes for November 12

4 Chem-Phys:

Welcome back! I hope Chemistry went well this past unit; hopefully you had the correct solutions to your test.

We are going to get into circuit analysis, where we will be most interested in learning the basic rules of resistor circuits (we were introduced to some of these last time). We now have 'discovered' Ohm's law, V = IR. We also were given the rules for series and parallel resistors: R_s = R1 + R2 + R3 + ... and R_p = (1/R1 + 1/R2 + 1/R3 +...)^-1.

There are two other even more important and fundamental rules for circuits of all kinds (at least the types we will study this year), called Kirchhoff's 2 rules.
1. In series, all voltage losses will add to the total voltage put into the circuit (i.e. the battery voltage), or V_total = V1 + V2 + V3 + ...
2. In parallel, the currents in the branches add up to the total current that went into the parallel set, or I_total = I1 + I2 + I3 + ...

Keep in mind that in series, there is ONE CURRENT going through everything on that path.

In parallel, EACH BRANCH HAS SAME VOLTAGE DIFFERENCE across it, and each branch can have different currents.

A few have suggested checking out a video on Band Theory, just to (hopefully) have a clearer sense of where energy bands come from. This may help with understanding conductors from insulators and semiconductors a little better.
More importantly for now, check out the video on how to analyze a combination circuit; the main goal is to figure out how many amps of current flow through every part of a circuit.

Take good notes, since these introductions to the rules will be used over and over again, not only with resistor circuits but also circuits with capacitors and inductors. In fact, the Kirchhoff rule for series (about voltage losses adding up to the input voltage) is, for us, the most important rule of all, and will allow us to write equations down for every circuit we work with.

For HW, try the circuit problems on page 5-6 of the packet; start error analysis of the last quizzam (solutions are online, in Gauss folder).

Thank you for all your support and understanding, as my family has gone through this episode with my mother! You will never know how much it means to me. I will be out Friday, which should be the last day. See you soon!  :-)