Engineering Circuit Complex Numbers question help

[ckeller]

Hey there, I have a question to answer and I'm unsure what exactly it is asking for, could anyone shine some light as to what this means? Is it two RC circuits in parallel??

"A circuit consisting of a 280 Ohm resistor in series with a 0.3 uF capacitor is connected to a supply operating at a frequency of 700Hz.
Use complex numbers to determine the values of the resistance "R" and capacitance "C" that when connected in parallel will represent the same value of impedance to the supply"

 

[sophiecentaur]

Google Thevenin's theorem.
If this is homework, it shouldn't really be in this forum. :-)

 

[ckeller]

Google Thevenin's theorem.
If this is homework, it shouldn't really be in this forum. :-)

Hey thanks for your reply, I will look into that.
It's not homework, just a practice question I was unsure of :)

 

[ckeller]

I think in other words..how would you get the same Impedance changing from a series RC circuit to a parallel RC circuit?

 

[sophiecentaur]

There will be a combination of RC in parallel that has exactly the same impedance as a given series RC. AT ONE FREQUENCY! (V. important to remember that).

 

[ckeller]

There will be a combination of RC in parallel that has exactly the same impedance as a given series RC. AT ONE FREQUENCY! (V. important to remember that).

Ah I will remember that thanks! I think I've worked it out... Rs^2 + Xs^2 / Rs = Rp

(Rs being series resistance, and Rp being parallel resistance) which comes to 2.331 kΩ

I also used Rs^2 + Xs^2 / Xs to calculate the Parallel Reactance which came to 861.326Ω

By using 1 / 861.32*2PI*700 I got 264nF.

Therefore C = 264nF & R= 2.331KΩ for the parallel circuit of the same impedance