Engineering RC circuit analysis using oscilloscopes

[blueincubi]

Homework Statement

this was a practical examination given to us.


[connected to CH1]
|----(1.8k ohms)-----|
|aaaaaaaaaaaaaaaaaa|
|aaaaaaaaaaaaaaaaaa(unknown resistance) [these 2 unknowns are ch2]
(~)aaaaaaaaaaaaaaa|
|aaaaaaaaaaaaaaaaa(unknown capacitance)
|--------------------|

so you've got a signal generator which is covered up, and the components are hooked up to the oscilloscope in the manner described above. the problem was to find out the the values of the unknown resistor and capacitor using the graph in the oscilloscope.


2. Equations

t/T = x/360

where:
t is the horizontal distance between the two curves
T is period
x is the angle

Ohm's law

The Attempt at a Solution

what i tried to do was to compare the voltage drop between ch2 and ch1 (which i treated as two separate impedances). and then divided it by the known R to get a value I which is the current for the whole mesh(?).

using that value I, i obtained the magnitude of the impedance of the RC component by Ohm's Law.

for the angle of the impedance, i compared the phase difference between the pure R impedance and the RC impedance. this is the part I am not sure of, is the angle x i get be the angle of the RC impedance (since purely resistive impedances are 0degs)?

but then, i assumed that the above were correct and managed to get a form a + jb, where j is sqrt(-1), so i took it as the a being the value of the resistor and b as the value of the capacitor?

 

[vk6kro]

I don't understand your diagram.

Is it like this:

[PLAIN]http://dl.dropbox.com/u/4222062/R-R-C.PNG

If so, maybe you could just refer to this diagram and say where the components connect to, or, you could modify the diagram using MS Paint and repost it?