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[Moved] finding quality factor(Q) for this circuit

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Vivvian GraCe Mosingki

Newbie level 2
Jun 13, 2015
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R1=10, R2=50, L=40m, c=0.1

can someone help how do i find quality factor for this kind of circuit??
i know that Q=R/wL, w=omega or Q=wRC..
but i cannot figure which R should i substitute into the R(equation)

A tricky question if not used to dealing with quality factors, the Q of the L is = 2.pi.f/R small R = higher Q.

Q for the cap, here you can use the parallel R1, Qc = R. 2.pi.f.C, larger R = higher Q.

The ckt Q is dominated by the lowest Q, Qt = Q1.Q2/(Q1+Q2)

Better answers welcomed....
hi thank u for the ans.. it really help me a lot.. but what if the question change a bit by adding an internal resistance at i(t)

In this case the Q of the ckt is unaffected, because the source is a current source, i.e. an infinite impedance to AC, therefore resonant currents do not flow in it and it contributes no damping effect or loss in Q, the result of the extra R in series with i(t) is to reduce the volts applied to the rest of the circuit, only. Different if you are driving with a voltage source...
In general, you can find the Q of such circuits (involving L, C and R) using the corresponding vector/phasor diagram.
The resulting total current I will be not in phase with the applied overall voltage V.
Then, the quality factor of the circuit is Q=tan(phi) if phi is the phase angle between V and I.

LvW, I think an example would help, if you are able to post one.....

I think, example diagrams showing the voltage and current phase relations (vector diagram) for simple circuits with reactive elements can be found in each textbook for basic electronics.

Of course, as an alternative, you can calculate the resulting total impedance Z of the circuit. The quality factor is Q=tan(phi)=Im(Z)/Re()Z).

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