# RLC circuit.. Whats the value of R???

Discussion in 'Homework Help' started by thepipersson1980, Aug 23, 2014.

1. ### thepipersson1980 Thread Starter New Member

Aug 23, 2014
8
0
Hi guys,
I really am stuck here so any advice would grateful

So my tutor has asked me to calculate impedance Z of a series circuit and all the info I had was,
A capacitor with the value of 300 uF
A inductor with a 800 mH
From there I have calculated the resonant frequency which is 10.3Hz AND the capacitive reactance which is 51.50 Ohms
So , what I have now is this;
R = Unknown
L = 800 mH
C = 300 uF
F = 10.3 Hz
Xc = 51.50
Xl = WL
W = 2pieF
Is it even possible to calculate Impedance Z, if I do not know the value of the resistor? and if so how???
Z= sqrt R^2 + (Xl - Xc)^2

I'm not after the answer to the impedance because I can work that out once I have the value of R, but I'm not convinced it can be done???

Many thanks for taking the time to read my question even if you can not answer it

2. ### ericgibbs AAC Fanatic!

Jan 29, 2010
3,325
591
hi,
Have you considered the possibility that the Resistance maybe assumed zero.?

E

3. ### MrChips Moderator

Oct 2, 2009
14,509
4,271
The resistance can be any value unless you provide some additional information that is dependent on resistance.

4. ### thepipersson1980 Thread Starter New Member

Aug 23, 2014
8
0
No I cant say I have, why would that be?

5. ### thepipersson1980 Thread Starter New Member

Aug 23, 2014
8
0
Do you think the tutor would be happy with this?

6. ### MrChips Moderator

Oct 2, 2009
14,509
4,271
Perhaps the tutor is trying to trick you? Go consult your tutor.

7. ### thepipersson1980 Thread Starter New Member

Aug 23, 2014
8
0
I do wonder this too, the original question was calculate the resonant frequency: calculate the capacitive reactance for a 300uF capacitor in series with a 800mH inductor.... Which as you can see I have answered and got correct but now he wants me to work out impedance Z??? most confusing???

Yet he can not be talking about any other question as they are all correct, according to him

8. ### ericgibbs AAC Fanatic!

Jan 29, 2010
3,325
591
hi 1980,
Lets assume that R=0 , in that case what do you calc the Impedance to be., at resonance.??

Last edited: Aug 23, 2014
9. ### thepipersson1980 Thread Starter New Member

Aug 23, 2014
8
0
Now you got me... 0.27???

10. ### ericgibbs AAC Fanatic!

Jan 29, 2010
3,325
591
Sounds close enough for me.

I make it:
Series Res&Ind&Cap:
R=0 XL=51.773 XC=51.506
Complex: 0 -j0.3
Polar0.2669988 Ohm 90 Deg

11. ### The Electrician AAC Fanatic!

Oct 9, 2007
2,378
355
You should carry more digits in your calculations, and consider what the definition of series resonance is.

12. ### shteii01 AAC Fanatic!

Feb 19, 2010
3,968
616
Basically there are no material, no references that would allow to find R. Therefore there are two choices:
* R is zero.
* R being a real number (it has no imaginary part) is part of Xl, Xc or both because Xl and Xc have real components.

13. ### thepipersson1980 Thread Starter New Member

Aug 23, 2014
8
0
Sorry for the late response,

I have taken Eric's advice, and have gone with what you have said to and made R zero... Xl and Xc are just because I have the values to work these out.

I will let you all know what is said when it comes back which will probably be next week now, In the mean time i would just like to thank everyone for giving their advice.

So, many thanks everyone