Coil electrodynamics

"Karl Roberts"

** The voltage across the coil varies from 4 to 12 volts in a sine wave fashion - IOW an 8 volt p-p sine wave with a DC component of 8 volts. So a current will flow in the coil that depends on it's impedance at the frequency of the sine wave AND it's DC resistance.

The mag field inside the solenoid will be in proportion to the instantaneous value of the combined currents.

** This is ambiguous.

What does '"split the coil in half " mean ?

Grounding the center point has no effect, on it's own.

Good enough for homework ??

... Phil

But don't two identical waves 180 degrees out of phase cancel to zero? Or does the symetrical DC component change this?

I gather from your kind reply, the answer to the last question is "yes".

This is what I am trying to visulaize/understand.

Karl Roberts

It melts.

ve

lts. So

try sci.electronics.basics. All the coil sees is the pd between its ends

NT

"Karl Roberts"

** Only if they are summed.

In your example the coil sees the * difference *.

As any load connected between two terminals does.

Very basic stuff.

Try " sci.electronics.basics " - next time.

... Phil

Karl, it may be easier to convince yourself that Phil is right by considering what would happen if *identical* signals were applied to each end of the coil. Now that's cancellation.

-- Joe

Can anyone please clarify the following for me?

Two part question:

If I take a solenoid and feed a positive DC offset sinewave (ie. 6V max 2V min) into one end and an inverted copy with a similar negative offset (ie -2V max -6V min) into the opposite, what, in terms of electrodynamics, occurs within the coil?

If I now split the coil in half and ground the center point, what happens now?

-----------

Do you realize that voltage is relative? You can add any voltage to one point as long as you add it to any other and the "physics" will not change.

So, your first case is identical to setting one side to 0 volts and the other side to (2sin(wt) + 4) + (-4 - 2sin(wt)) = 0. So both ends of the coil are at the same voltage. I could have set one end to Zeta(wt)^w + cos(wsinw(wt))^t and wouldn't have changed anything.

In the second case when you ground the center you end up with two coils. You can separate them mentally or even physically since you know(or forced) the center(or even some other point) to be a certain value. It is exactly the same when we know(force or decide) that something is "ground".

Note that this is distinctly different from the first case. In the first case we have one coil and the second case we have two... but each one similar to the others.

Anyways, if you think about it a bit you shouldn't have any issues. Use resistors instead of coils. The only difference with coils is that the voltage drop across the coil may not be linear due to self and mutual electromagnetic effects and fringe effects.

--
The voltage across the coil will cause a current through the coil
which will only be limited by the impedance of the coil at the
frequency in question.

What? ... and get answers from more people like me.

Karl

--
Funny! :-)

Karl Roberts wrote on 29/10/2011 :

Well you know Electronics BASICS is for people like you trying to understnd Electronics And Electronics DESIGN is for people who actually have learnt some basics and are trying to design something.

--
John G.

"Don Mack"

" If I take a solenoid and feed a positive DC offset sinewave (ie. 6V max 2V min) into one end and an inverted copy with a similar negative offset (ie -2V max -6V min) into the opposite, what, in terms of electrodynamics, occurs within the coil? "

** That is completely absurd.

The two voltage sources are summed in series, so the total is 8 + 4sin(wt).

** Drivel.

** More absolute drivel. ** Take your own advice - fool.

... Phil

In that case, given my original example of a + and - 2VDC offset for each idendtcal sinewave, there would be a residual DC current flow at

4V from one end of the coil to the other.

Going back to having one sinewave inverted from the other, I understand (now) the voltages add to 12 and the composite signal is riding on the same 4V current.

Is that all correct?

OK, that's my last follow-up.

Karl Roberts

--
So, then, why are _you_ posting here?

Seven posts so far and you've done nothing but negatively kibitz and
kvetch and try to set yourself up as an authority of some kind without
actually contributing anything meaningful.

Why don't you just go away and save us all the trouble of driving you
to suicide with logic?

"Karl Roberts" " J.A. Legris"

** FFS pal - you just contradicted yourself.

The new case is VERY DIFFERENT from yuor example !!.

** Thick as a plank.

The offset voltage is 8 volts - cos that is the AVERAGE value of 8 +

4sin(wt)

The sine wave both adds to and subtracts from the DC offset - giving 4 and

12 as the min and max values.

... Phil

John Fields expressed precisely :

No I just explained the difference. And I try not to be abusive. And I try not to show how clever I am with net lists that basics enquirers have no chance of understaning.

--
John G.

"Karl Roberts" "Phil Allison"

** Hey d*****ad.

Have a look and see who is supplying most of the answers.

The NG is about basic electronics, like your question.

... Phil

--
Explained?

No.

What you did was to insult the OP by trying to relegate him to a forum
with a lower Q than sed when you had no right to.

But you wouldn't know anything about that, would you?

Where do see the application here being that of a solenoid? He did not mention one.

Since you seem to think he is referring to a solenoid maybe?