Zero Ohms?
Looking into the circuit (shwon in the video) I see a PARALLEL connection of both elements (L and C), am I wrong?

Hi,

You only quoted PART of my reply. You should NOT do that. That takes some of the information out of context. That's why you are assuming a predetermined context when I set the new context myself.

Here is the original quote:

When we do a calculation like that we take L and C to be ideal, and because there is no "R" there is no resistance. At physical resonance, the L and C become equal to a resistance of zero Ohms. In real life that would probably be rare, but in theory it is always taken just like that, zero. That's so that it makes it simpler to understand the underlying mechanism.

For a series L and C we end up with:
Z=j*w*L-j/(w*C)

and when we set w=1/sqrt(L*C) we get exactly:
Z=0

You see the entire quote (that matters) also includes the calculation for a SERIES circuit with L and C only. Later in that reply, I add R to make it clear how the R affects the total impedance.

The parallel calculation is of course different:
Z=(j*w*L)/(1-w^2*C*L)

and at physical resonance this becomes infinite.

It's probably still good that we looked at both of these situations though.

 

Hi,
You only quoted PART of my reply. You should NOT do that. That takes some of the information out of context. That's why you are assuming a predetermined context when I set the new context myself.

I'm sorry if I misunderstood something in your post.
But the video in question clearly deals with a parallel connection - and I really thought you'd made some kind of “typo.”
I’m sure I quoted you correctly and in full, BUT:
It wasn’t entirely clear to me that your sentence mentioning “zero ohms” referred to another post in which a series connection was mentioned.
(The beginning of your sentence was " When we do a calculation like that..." and it was not clear tome what you mean with "like that")
Sorry for the misunderstanding.
Regards
LvW

 

I'm sorry if I misunderstood something in your post.
But the video in question clearly deals with a parallel connection - and I really thought you'd made some kind of “typo.”
I’m sure I quoted you correctly and in full, BUT:
It wasn’t entirely clear to me that your sentence mentioning “zero ohms” referred to another post in which a series connection was mentioned.
(The beginning of your sentence was " When we do a calculation like that..." and it was not clear tome what you mean with "like that")
Sorry for the misunderstanding.
Regards
LvW

Hi,

Oh no, no big deal. I just figured if I show the calculation with the text then it would be apparent.
Sorry it did not match the video.

What I thought was that with the series circuit it is more intuitive because we can see all the terms independently, so we can see how the real and imaginary parts cancel. One is positive and the other is negative, so when they are equal they cancel. It's harder to show that with the parallel version.

 

Hi,

Oh no, no big deal. I just figured if I show the calculation with the text then it would be apparent.
Sorry it did not match the video.

What I thought was that with the series circuit it is more intuitive because we can see all the terms independently, so we can see how the real and imaginary parts cancel. One is positive and the other is negative, so when they are equal they cancel. It's harder to show that with the parallel version.

OK - I know what you mean.
However, working with conductances rather than impedances, it is also very simple to show how both parts cancel in a parallel combination (Yp=YL+Yc)

 

OK - I know what you mean.
However, working with conductances rather than impedances, it is also very simple to show how both parts cancel in a parallel combination (Yp=YL+Yc)

Hi,

Oh you mean using the admittance. Yes, that's not too bad, but then the cancelation ends up in the denominator and that also leads to zero in the denominator, which of course leads to infinity.

So it is for series:
j*w*C-j/(w*L)=0

vs for parallel:
1/[j*w*C-j/(w*L)]=infinity

I do like the idea of using the admittances though. It seems to clearly show how an infinity comes about if they know how that works (0 in the denominator).