1. Lab #5: RC AC Circuits remember how AC circuits containing capacitors and resistors behave.

2. Caps and AC sources Voltage across cap is same as voltage across supply. When the voltage is changing quickly, the charge also has to change quickly -> big current Size of the current depends on the frequency Get biggest currents at high frequencies

3. Presence of the capacitor affects the size of the current in the circuit in a frequency-dependent way. “phases” of signals across voltage source, resistor, and capacitor differ math is most easily done by modeling the voltage source as instead of and an imaginary reactive for the capacitor (to shift its affect on the current by 90 degrees) and then taking the real part at the end. AC RC Circuits As per last week, be careful with the grounds!

4. The Math What is the current? Any complex number can be written as a magnitude and an angle in the complex plane. Easy to read off mag of current. Current (and thus voltage across the resistor) is shifted in phase from the voltage source by 

5. V across R and across C Again, V across C tends to be large when V source is changing quickly

6. hints lab starts pg 47 include syst errors for R and C measurements, but not for t and V measurements with scope. MAKE SURE DUTY CYCLE IS ALL THE WAY COUNTER CLOCKWIZE! pay attention to the scale (v/division) on ch1,ch2 VERY IMPORTANT WHEN DOING PART C!!! phase shift can not be greater than pi remember “compare” is a mathematical operation involving a chi^2 test make sure the wave oscillates around zero (using the offset knob). Make sure there is no dc offset. remember, V R lags V IN by phi

7. changes use the 10k resistor and the 0.1  F cap for Part A. in part A.1, where it says “between the zero crossings”, I suggest using the time between the maximums of the waveform instead. In the lab, when it says do 10 measurements, do 7 instead. For part A.1, capture your waveform with wavestar and paste into lab report. A-2. replace “qualitively” with “qualitively and quantitatively”. In B, don’t go as low as 10 Hz. Do 50-500 Hz. B.1. errors are tricky!

8. Errors

9. errors You measure dt. Calc y=cotan(2*pi*f*dt). What is error on y?