# A simple theoretical question regarding RLC

Discussion in 'Homework Help' started by sstbrg, Nov 29, 2008.

1. ### sstbrg Thread Starter Active Member

Nov 29, 2008
54
0
Let's say I've got a non-ideal RLC circuit (meaning that both Zc and Zl have unknown resistances Rc and Rl besides their reactances).

I can also measure the voltage across those three elements, and obviously I know the total voltage (for example 120V with f=60Hz, but can be any |V| and f).

Can I somehow find out Rl, Rc, Xl and Xc ?

Last edited: Nov 29, 2008
2. ### mik3 Senior Member

Feb 4, 2008
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63
Yes, if you know the voltage across and current through each component then you can calculate the total impedance of this component (you have to take care of the angle between the voltage and current for each component).
Then, once you calculate the total impedance, say for the inductor, you can extract the real part (Rl) and the imaginary part (Xl) out of this impedance.
This is easy for the inductor (if you consider the inductor as an ideal inductor in series with a resistor and dont mention the small capacitance it introduces).
However, for the capacitor, if you model it as an ideal capacitor with a resistor (leakage resistance) in parallel with it, things are more complicated. You have to play with complex numbers.
The complexity of analysis depends of the degree of accuracy you want to make calculations. All components contain parasitic resistance, capacitance and inductance. How complex will be the analysis depends on how much do you care about each of them.

3. ### sstbrg Thread Starter Active Member

Nov 29, 2008
54
0
Well, I can find Zl and Zc (the resistor has a known value) obviously, but I don't really understand how to find the real part and the imaginary (reactance) part of the impedance with that data only.
If I can really measure its Re part, I guess I can, but with the above data only, it's quite impossible right?

Let's assume I'm modeling them as ideal elements with resistors in series.

Last edited: Nov 29, 2008