# Resonance series and parallel

Discussion in 'Homework Help' started by xx123321, May 4, 2011.

1. ### xx123321 Thread Starter New Member

Apr 27, 2011
15
0
hi,every guys,i am currently having difficulty with a RLC resonant circuit.

First of all,what's the relationship between VR and VC?
In addition, i am confused by some terms in resonant circuit.
what're the meaning of following terms:
1-fs
2-fp
3-Qs
4-Ql
5-Qp

2. ### beenthere Retired Moderator

Apr 20, 2004
15,815
282
You might get better help if you post the circuits. You do know that LC resonance occurs when Xc = Xl?

3. ### xx123321 Thread Starter New Member

Apr 27, 2011
15
0
UPDATE the circuit as follow,

I know that resonance occurs when XL=XC.

4. ### beenthere Retired Moderator

Apr 20, 2004
15,815
282
That's a series circuit. No frequency is given from the source, so you need to find the F that makes Xc = Xl. R is there for a reason.

5. ### xx123321 Thread Starter New Member

Apr 27, 2011
15
0
Assume that's a resonant circuit, so Xc=Xl=30 ohm ,it that right?
Then how about my questions posted at #1 ?

6. ### jegues Well-Known Member

Sep 13, 2010
735
43

Starting with Xc=Xl, can you obtain $f_{o}$?

7. ### xx123321 Thread Starter New Member

Apr 27, 2011
15
0
frequency is 5k Hz

8. ### jegues Well-Known Member

Sep 13, 2010
735
43
Can you show us how you obtained a value of 5KHz?

9. ### xx123321 Thread Starter New Member

Apr 27, 2011
15
0
I am sorry about that i haven't express the question clearly,the question haven't gave any frequency,the source is 50mV only.

Here is the original question:
The question is "Refer to the resonant circuit in figure 1 (posted at #3) ,determine:
(a)the value of Xc --->is the answer 30ohm?
(b)total impedance
(c)current
(d)Vr,Vl and Vc at resonance
(e)The relationship between Vr and Vc

I have figured out (a),(b),(c),(d) but i am stuck at (e)

10. ### t_n_k AAC Fanatic!

Mar 6, 2009
5,448
782
The OP's original question asked what was the relationship between VR & VC in the series circuit - at resonance.

There's no need to find the resonant frequency.

At resonance VR & VC are orthogonal and for the given circuit have a magnitude ratio |VR/VC|=1/3. VR will be 50mV and in phase with the source E.

One could guess the context of the other matters - presumably they relate to resonant frequencies and Q factor values in series and parallel resonant circuits. I don't think anyone is really interested in explaining these terms when they are well defined in any number of text books or web pages.

Such as ....