# RLC Circuit Current

Discussion in 'Homework Help' started by Sgt.Incontro, Oct 20, 2013.

1. ### Sgt.Incontro Thread Starter Member

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Hi all,

I need help with the first question from this problem sheet I am doing. Of course I am not asking anyone to just post the answer, but some guidance in the right direction would be appreciated. That way I can attempt it, and post my answer for scrutinizing ...

Question:

Thank you.

2. ### WBahn Moderator

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Let's do it the other way around. Post YOUR best attempt to solve YOUR homework problem -- it doesn't have to be complete or correct, but it does have to be present. We can then use that to see where you are and then provide feedback to help move you in the right direction.

3. ### Sgt.Incontro Thread Starter Member

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Hi WBahn,

I think the lecturer only wants a brief description of what happens, and not a complex mathematical answer.

Of course I am able to provide you with what I think:

To begin with, for part a), I wrote:

When voltage is first applied after closing the switch (at t=0), the inductor impedes current flow in the circuit, so the current = 0. After time t=0, the current will follow a second order natural response characteristic as shown below

((P.S: I may be also interested in the mathematical answer later on.))

4. ### WBahn Moderator

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You answer is basically correct, but it would be good to indicate if the initial current (after t=0+) will be positive or negative.

How about a shot at part b)?

5. ### Sgt.Incontro Thread Starter Member

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Hi WBahn,

I will post my answers for b) once I get home, are you able to just write the characteristic equation for part A or describe it so I know whether my answer is correct? Thanks.

6. ### WBahn Moderator

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Ah, no. Post your answer and we will look it over and let you know if it is correct and, if not, give you hints to help you find what is wrong with it and how to proceed. And again, we don't require full-up solutions. Just get as far as you can and show your work up to that point.

7. ### Sgt.Incontro Thread Starter Member

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Thanks. I only asked if you could do that so it would save time - as this is due very soon. (If I were to cheat with this question, I would only be cheating myself.)

Anyway, I have scanned my (mathematical) solutions for part a) and part b).

I will also upload the written explanation for part b) as I said yesterday.

8. ### Sgt.Incontro Thread Starter Member

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Solutions:

As soon as both s1 and s2 are closed (at t=0), the current will be equal to V(0)/R, as the infinite instantaneous impedance of the inductor will act as an open circuit.

Part a) & b) mathematical answers:

http://postimg.org/image/somif17fl/

EDIT: Realized the silly mistake in part b) where I did the parallel impedance wrong. (Ignore that.)

Last edited: Oct 23, 2013
9. ### Sgt.Incontro Thread Starter Member

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Bump...... (>10char)