# need help with RLC circuit

Discussion in 'Electronics Homework Help' started by Mugiwara303, Jun 14, 2015.

1. ### Mugiwara303

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Jun 14, 2015 can anyone solve this circuit for me! thanks!

5,164
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Dec 18, 2013
How far have you got? You need to show us what you have done and what you don't understand first.

3. ### Mugiwara303

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Jun 14, 2015 are the question 2 and 3 correct?

4. ### Minder

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Apr 24, 2015
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5. ### Mugiwara303

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Jun 14, 2015
thank you for this, i need the solution, because this one is RL//C it is confusing me...

6. ### Laplace

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Apr 4, 2010
The formula used in #2 is a shortcut used when the phase angle between vectors is 90°. Why do you think that would apply here?

7. ### Mugiwara303

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Jun 14, 2015
can anyone give me the solution, don't suggest me what to do because i don't know what to do...

8. ### Laplace

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Apr 4, 2010
The only solution is to calculate the complex impedance of the circuit and use that to find the current, I=V/Z. Or else find the magnitude & phase of each component current, then use the general method for adding vectors to get the total current.

9. ### Mugiwara303

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Jun 14, 2015
can i do Z = √(r2+XL2)+Xc then i=v/z

and what about IT = u/Zrl + u/Xc

10. ### Laplace

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Apr 4, 2010
No. It is not possible to do this problem with just magnitudes, the phase angles must also be accounted for. You need to use complex algebra or a phasor diagram.

11. ### davennModerator

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Sep 5, 2009
The respondants are doing the right thing
listen to them and learn .... make a little effort

we will guide you to a solution ... we wont just hand one to you
you need to be able to learn how to do this yourself ... else you will never learn how

there wont be anyone in an exam to just hand you a solution

Dave

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12. ### Mugiwara303

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Jun 14, 2015
its really complicated for me to explain to you LoL! i need to know this as fast as i can i don't have time... can anyone give me the detailed solution and i will understand then! thanks in advance.

13. ### Harald KappModeratorModerator

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Nov 17, 2011
That is not how this forum works. Understand and then find the solution.

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14. ### Mugiwara303

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Jun 14, 2015
i am sorry then! i thought i will get some help here, not telling me what to do, if i knew i would do it my self... i don't know whats the problem if someone can give me the solution, then i will understand and apply for other problems...

15. ### Harald KappModeratorModerator

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Nov 17, 2011
The impedance of an inductr is XL =2*Pi*f*L.
The impedance of a capacitor is XC = 1/ ( 2*Pi*f*C).
The impedance of a resistor is ZR = R.

By applying the parameters you are given (X, f) you can calculate L and C for this circuit.

From R, L, C and F and using
The impedance of an RLC circuit, whichever way it is constructed, can be calculated from the same equations as for a purely resistive circuit, just replace each element in the equation by the equivalent complex impedance:
• components in series. Ztotal = Zcomp + Zcomp2 +...Zcompn
• components in parallel: 1/Ztotal = 1/Zcomp1 + 1/Zcomp2 + ... 1/Zcompn
From these basic equations plus aplication of Kirchhoff's laws (and equivalently Thevenin theorem and / or Norton theorem) you can calculate the RLC circuit's parameters. You'll have to use complex math. You should have learned this by now, otherwise giving you this task makes no sense. You can read up and refresh your knowledge a bit here or here.

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16. ### Mugiwara303

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Jun 14, 2015 is this right?

17. ### Ratch

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Mar 10, 2013
Is It = 11.57 supposed to the total current? There is a capacitor and an inductor in the circuit. Are not the currents in the capacitor and inductor branches supposed to have a orthogonal component, or what you might call an imaginary component? The same applies to the total current. What are the real and orthogonal components of all the currents?

Ratch

18. ### Laplace

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Apr 4, 2010
It may help one's understanding to see what is going on with the help of a phasor diagram. But first note that capacitive reactance, X{C}, and inductive reactance, X{L} are given in the problem statement; however, impedance is required to perform the circuit calculations. Impedance can be obtained from the given reactance.

Z{L} = jωL = j∙X{L}

Z{C} = 1/(jωC) = (1/j)∙X{C}

Now use complex algebra to calculate the branch currents I{C} & I{L}, then convert the complex vectors to polar form and plot them on the phasor diagram as shown. The total current I{T} is found as the vector sum of the branch currents I{C} & I{L}.

I{C} = 220/Z{C}

I{L} = 220/(R+Z{L})

I{T} = I{C} + I{L}

Note that the attached phasor diagram does not include a current scale so you'll need to find the solution yourself.   