Test 2

Monday, Nov 20 - Bring:

  • Calculator
  • Writing instruments
  • a page of notes that you've prepared ahead of time.

Test resubmissions

If you are dissatisfied with how you did on several (or more) of the exam problems, you may resubmit:

  • Whether you scored high or low on the in class exam, or on the resubmission... It always makes a good impression on me when you re-submit. I think: "Wow, here's a person who is not just giving up, but is willing to work to figure out what they didn't quite get the first time!"
  • Get a copy of the test from Paul,
  • Turn in your resubmitted exam at (or before) the beginning of class on Friday morning.

  • You do not need to resubmit the whole exam. You may resubmit just a few problems.
  • You may consult our class notes, internet resources, textbooks, even other people.
  • No credit will be given if you just write down the correct answer. To receive credit you must include supporting work: Show how you calculated, or what steps you went through to get to your answer; Explain why you placed a piece of code where you did in the skeleton;
  • For each resubmitted problem, I'll replace your in-class score with the average of your in-class exam and your after-class resubmission.

Review / Guide

This is not exhaustive, but is meant to list some of the main content you should know and be able to use to solve problems:

Ohm's Law / Kirchoff

Solving problems / circuits

  • $V=IR$
  • At any point $\sum I_\text{in}=\sum I_\text{out}$.
  • Voltage drops from a starting point to an ending point are the same for any connecting path.
  • Ideal wire: 0 resistance / voltage is the same throughout any wire-only segment.
  • Total resistance of resistors in series
  • Total resistance of resistors in parallel

Voltage dividers & loading

  • typical circuit: voltage divider with load across in parallel with "bottom" resistor.
  • Voltage drops of Thev. device depending on load.

Pulse Width Modulation

  • Going back and forth between frequency and period via $f=1/\tau$
  • Reading period, amplitude, p-to-p voltage off oscilloscope traces
  • Duty cycle

Dealing with units

  • mA, V, mV, $\Omega$, K$\Omega$.
  • seconds, milliseconds, microseconds
  • Hz = cycles (or 'periods') per second, kHz, Mhz

Diode circuits

  • 2-step analysis of diode circuits:
    1. Assuming no current is flowing through any diode...What is the voltage difference across the diodes? (magnitude and direction)
    2. if the voltage difference is greater than $V_f$ or $V_b$, assume the diode voltage drop instead

Op Amps

  • Two rules of op amps
  • calculate gains using two rules
  • Output / input impedance

RC circuits

  • Qualitatively, a capacitor acts
    • like a wire for quick changes: current flows quickly and voltage changes quickly,
    • like a break in the wire for slow changes: currently hardly flows
  • Qualitative response to square waves.
  • Quantitative response to square waves: exponential decay: $V=V_0e^{-t/RC }$ and exponential approach to a final voltage:$V=V_0(1-e^{-t/RC})$
  • exponential time constant $RC$, and units (Ohms$\cdot$Farads = seconds)
  • Identify low / high pass filter circuits.
  • Approximate behavior of a filter:
    • Calculate corner frequency $f_0=\frac 1 {2\pi RC}$
    • "Corner" at $(f_0,1)$
    • On "passsing" side, $|V_\text{out}/V_\text{in}|$ approaches 1 and phase shift $\to$0.
    • On "suppressing" side, $|V_\text{out}/V_\text{in}|$ drops off by one factor of 10 for every change of frequency by a factor of 10, and phase shift $\to$90 degrees.
  • Using a high- or low-pass filter to filter out a low- or high- signal from a compound signal.
  • Nothing about decibels.