Forums

Coil electrodynamics

Started by Karl Roberts October 27, 2011
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?

Karl Roberts




"Karl Roberts"

> 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? >
** 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.
> If I now split the coil in half and ground the center point, what > happens now?
** 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
On Fri, 28 Oct 2011 12:10:28 +1100, "Phil Allison" <phil_a@tpg.com.au>
wrote:

> >"Karl Roberts" > >> 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? >> > >** 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. >
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
Karl Roberts wrote:
> 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?
It melts.
> > If I now split the coil in half and ground the center point, what > happens now? > > Karl Roberts > > > >
On Oct 28, 9:00=A0am, karlrobe...@infoline7.com (Karl Roberts) wrote:
> On Fri, 28 Oct 2011 12:10:28 +1100, "Phil Allison" <phi...@tpg.com.au> > wrote: > > > > > > >"Karl Roberts" > > >> 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? > > >** =A0The voltage across the coil varies from 4 to 12 volts in a sine wa=
ve
> >fashion =A0- =A0 IOW an 8 volt p-p sine wave with a DC component of 8 vo=
lts. 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. > > 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
try sci.electronics.basics. All the coil sees is the pd between its ends NT
"Karl Roberts"


> But don't two identical waves 180 degrees out of phase cancel to zero?
** 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
On Oct 28, 6:38=A0am, "Phil Allison" <phi...@tpg.com.au> wrote:
> "Karl Roberts" > > > But don't two identical waves 180 degrees out of phase cancel to zero? > > ** =A0Only if they are summed. > > =A0In your example the coil sees the * difference *. > > =A0As any load connected between two terminals does. > > =A0Very basic stuff. > > =A0Try " sci.electronics.basics " =A0 - =A0next time. > > ... =A0 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

"Karl Roberts"  wrote in message news:4ea9fb6c.174734@news.tpg.com.au...

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.



On Fri, 28 Oct 2011 00:55:32 GMT, karlroberts@infoline7.com (Karl
Roberts) wrote:

>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?
--- 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. ---
>If I now split the coil in half and ground the center point, what >happens now?
--- The center tap will always be at zero volts, as will ground, so nothing will happen: Version 4 SHEET 1 1228 784 WIRE 64 -160 -80 -160 WIRE 64 -112 64 -160 WIRE 64 0 64 -32 WIRE 176 0 64 0 WIRE 64 32 64 0 WIRE 176 32 176 0 WIRE 288 48 224 48 WIRE -80 192 -80 -160 WIRE 64 192 64 112 WIRE 288 192 288 48 WIRE -80 368 -80 272 WIRE 64 368 64 272 WIRE 64 368 -80 368 WIRE 176 368 176 112 WIRE 176 368 64 368 WIRE 224 368 224 96 WIRE 224 368 176 368 WIRE 288 368 288 272 WIRE 288 368 224 368 WIRE -80 480 -80 368 FLAG -80 480 0 SYMBOL ind 80 128 R180 WINDOW 0 36 80 Left 2 WINDOW 3 36 40 Left 2 SYMATTR InstName L2 SYMATTR Value 1 SYMATTR SpiceLine Rser=.1 SYMBOL ind 80 -16 R180 WINDOW 0 36 80 Left 2 WINDOW 3 36 40 Left 2 SYMATTR InstName L1 SYMATTR Value 1 SYMATTR SpiceLine Rser=.1 SYMBOL voltage -80 176 R0 WINDOW 3 24 96 Invisible 2 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V1 SYMATTR Value SINE(4 2 10) SYMBOL voltage 288 176 R0 WINDOW 0 -53 5 Left 2 WINDOW 3 -242 110 Invisible 2 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V4 SYMATTR Value PULSE(0 1 1 1E-6 1E-6) SYMBOL sw 176 128 R180 WINDOW 0 32 15 Left 2 WINDOW 3 32 44 Left 2 SYMATTR InstName S1 SYMBOL voltage 64 288 R180 WINDOW 3 24 96 Invisible 2 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V2 SYMATTR Value SINE(4 2 10) TEXT -56 400 Left 2 !.model SW SW(Ron=1u Roff=1G Vt=0.5 Vh=0) TEXT -56 432 Left 2 !.tran 0 2 0 -- JF
On Fri, 28 Oct 2011 21:38:06 +1100, "Phil Allison" <phil_a@tpg.com.au>
wrote:


> Try " sci.electronics.basics " - next time. >
What? ... and get answers from more people like me. Karl