 ### Network # need help with RLC circuit

#### Mugiwara303

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

#### Arouse1973

Dec 18, 2013
5,178
How far have you got? You need to show us what you have done and what you don't understand first.

#### Mugiwara303

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

#### Mugiwara303

Jun 14, 2015
8
thank you for this, i need the solution, because this one is RL//C it is confusing me...

#### Laplace

Apr 4, 2010
1,252
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?

#### Mugiwara303

Jun 14, 2015
8
can anyone give me the solution, don't suggest me what to do because i don't know what to do...

#### Laplace

Apr 4, 2010
1,252
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.

#### Mugiwara303

Jun 14, 2015
8
can i do Z = √(r2+XL2)+Xc then i=v/z

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

#### Laplace

Apr 4, 2010
1,252
can i do Z = √(r2+XL2)+Xc then i=v/z
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.

#### davenn

Moderator
Sep 5, 2009
14,196
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

• Harald Kapp

#### Mugiwara303

Jun 14, 2015
8
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.

#### Harald Kapp

##### Moderator
Moderator
Nov 17, 2011
13,337
can anyone give me the detailed solution and i will understand then! thanks in advance.
That is not how this forum works. Understand and then find the solution.

• davenn

#### Mugiwara303

Jun 14, 2015
8
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...

#### Harald Kapp

##### Moderator
Moderator
Nov 17, 2011
13,337
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.

• Mugiwara303

#### Mugiwara303

Jun 14, 2015
8 is this right?

#### Ratch

Mar 10, 2013
1,098 is this right?

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

#### Laplace

Apr 4, 2010
1,252
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. #### Arouse1973

Dec 18, 2013
5,178 is this right?

Your IC and IL seem correct but I don't think your IT is. It's too high.

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