# Finding unknown values in a circuit

Discussion in 'Homework Help' started by labhelp, Jan 28, 2010.

1. ### labhelp Thread Starter New Member

Jan 28, 2010
28
0
In my lab we were given 3 black boxes and a sheet with 3 different circuits(shown in the attached pdf on page 3). We were then told to find out which box went with which circuit then find the values of all of the components. We found the transfer functions for each circuit then ran a voltage sweep on the actual circuit to see what the graph would do. We figured out which box went with which circuit and also figured out the values of the resistors. We are stuck on how to figure out the value of the capacitors. We have a lot of equipment available like a Oscilloscope, DMM, waveform generator, and a DC power supply.

Can I get some advice on how i can obtain the capacitances for each of the circuits? thanks in advance.

• ###### EE 230 Lab 3 Fall 2006 Fundamental Properties.pdf
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Last edited: Jan 28, 2010
2. ### kdillinger Active Member

Jul 26, 2009
141
3
You forgot the PDF.

Jan 28, 2010
28
0

4. ### beenthere Retired Moderator

Apr 20, 2004
15,815
283
You do know that capacitors' impedance changes with frequency?

5. ### labhelp Thread Starter New Member

Jan 28, 2010
28
0
yeah i do i'm just having trouble grasping what I need to do to figure it out

6. ### beenthere Retired Moderator

Apr 20, 2004
15,815
283
Pick two frequencies to apply to the box input. Calculate Xc for those frequencies, and use that to solve the network and get the magnitude of the output for both situations. The difference between the two will let you determine the size of the capacitor.