How to Calculate Maximum Current in an RLC Circuit?

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Homework Help Overview

The problem involves calculating the maximum current in an RLC circuit with given values for resistance, inductance, and capacitance, driven by a sinusoidal voltage source. The participants are exploring the relationship between voltage, current, and impedance in the context of alternating current (AC) circuits.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss the calculation of impedance and the maximum current, questioning how to apply the results from the impedance calculation to find the maximum current. There is consideration of using AC analogs to Ohm's law and the implications of phase shifts between voltage and current.

Discussion Status

Some participants have suggested using the relationship Z = V/I to connect maximum voltage and maximum current, while others express uncertainty about how to proceed with the calculations. The discussion reflects a mix of interpretations and approaches without a clear consensus on the next steps.

Contextual Notes

Participants note the challenge of relating voltage and current due to phase shifts in AC circuits. There is also mention of needing to work with the differential equation governing the circuit, indicating a complexity in the problem setup.

radicaled
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The problem
The exercise goes like this:
A sinusoidal source v(t) = 40 sin(100t) its applied to a circuit RLC with L=160 mH, C=99 μF and R=68Ω.

Calculate
a) the impedance of the circuit
b) the maximum current

My solution
a)
If v(t) = 40 sin(100t) --> ω=100Hz

Z= [itex]\sqrt{R^{2} + \left(Xl-Xc\right)^{2}}[/itex]

Z = 108,86 Ω

b)
I know that
[itex]ic(t)= C\frac{dv}{dt} -> v(t)= \frac{1}{C}\int idt[/itex]
[itex]v(t)=Ri(t)[/itex]
[itex]v(t)= L \frac{di}{dt}[/itex]

[itex]v(t)=Ri(t) + L \frac{di}{dt} + \frac{1}{C}\int idt[/itex]

Ok, I'm stuck here. I know v(t), R, L and C. But I'm not sure how to get it.

Thanks for you help
 
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Can you use your result from part (a)? [Hint: Is there an AC analog to Ohm's law?]
 
Last edited:
I guess you could. I'be been thinking this exercise a couple of hours and I miss it. But you can use the sinusoidal variables with the rest?
Z=V/I
 
You may use Z = V/I to relate the maximum voltage and the maximum current.

But remember that the maximum voltage does not occur at the same instant of time as the maximum current (phase shift). So, you should not try to use Z = V/I to related the current and voltage at the same instant.
 
Ok, but if I want to calculate the maximum current I'm going to need the [itex]v(t)=Ri(t) + L \frac{di}{dt} + \frac{1}{C}\int idt[/itex] ecuation, and I'm stuck there.
Otherwise, there is any other way to obtain the max current with the data I have?
 
radicaled said:
Ok, but if I want to calculate the maximum current I'm going to need the [itex]v(t)=Ri(t) + L \frac{di}{dt} + \frac{1}{C}\int idt[/itex] ecuation, and I'm stuck there.
Otherwise, there is any other way to obtain the max current with the data I have?

Yes, As I indicated above. You can use Z = V/I to relate the maximum voltage and current. Thus, solve this equation for I and plug in the values for Z and the maximum voltage.
 

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