# Does a coil also have a capaciotance?

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Joe Snodgrass
Guest

Fri May 13, 2011 3:47 am

It seems to go against everything they taught us in class, but the
various turns are closely spaced conductors, separated by a dielectric
layer, just like the plates of a capacitor. TIA.

Artemus
Guest

Fri May 13, 2011 3:47 am

"Joe Snodgrass" <joe.snod_at_yahoo.com> wrote in message
Quote:

It seems to go against everything they taught us in class, but the
various turns are closely spaced conductors, separated by a dielectric
layer, just like the plates of a capacitor. TIA.

Yes. Its referred to as distributed capacitance. It has resistance too.
Likewise capacitors have L & R too.
Welcome to the real world which they didn't teach you about.
Art

John Larkin
Guest

Fri May 13, 2011 3:47 am

On Thu, 12 May 2011 18:47:22 -0700 (PDT), Joe Snodgrass
<joe.snod_at_yahoo.com> wrote:

Quote:

It seems to go against everything they taught us in class, but the
various turns are closely spaced conductors, separated by a dielectric
layer, just like the plates of a capacitor. TIA.

Absolutely. Always. Lots of coils are spec'd to have an SRF,
self-resonant frequency. The impedance peaks at the SRF, and drops
above that frequency as the capacitance starts to dominate. Given SRF
and the inductance, you can calculate the equivalent capacitance, as
though all the C were connected to the ends of the inductor. Of
course, in real life the capacitance is distributed all over the
place.

The turns also have capacitance to the universe; and to the core, and
to other windings, if any.

John

Phil Allison
Guest

Fri May 13, 2011 5:07 am

"Joe Snodgrass"
Quote:

It seems to go against everything they taught us in class, but the
various turns are closely spaced conductors, separated by a dielectric
layer, just like the plates of a capacitor.

** As others had said, any practical coil of wire has a self resonant
frequency due to it's capacitance. By measuring this frequency, one can find
the effective parallel capacitance - which may be from a few pF upwards.

Likewise, all practical capacitors have lead inductance and hence a self
resonant frequency - this time it's series resonance so the impedance value
drops to a minimum then rises. For most caps with wire leads each end, the
inductance is some value between 10nH and 40nH producing self resonant
frequencies of a few kHz to tens of MHz, depending on the cap value.

In both cases, the usual formula F = 1/( 2.pi. sq rt L.C ) applies.

..... Phil

Uwe Hercksen
Guest

Fri May 13, 2011 7:29 am

Joe Snodgrass schrieb:
Quote:
It seems to go against everything they taught us in class, but the
various turns are closely spaced conductors, separated by a dielectric
layer, just like the plates of a capacitor. TIA.

Hello,

every real component has all three properties, resistance, inductance
and capacitance. There is no component with only one or two of these
properties.

Bye

Uwe Hercksen
Guest

Fri May 13, 2011 10:14 am

Bill Sloman schrieb:

Quote:
Though you can often get away with ignoring the resistance of a super-
conducting inductor.

Hello,

even in this case there is resistance, the isolation resistance of the
conductor to ground.

Bye

Phil Allison
Guest

Fri May 13, 2011 10:21 am

"Uwe Hercksen"
Quote:

Bill Sloman schrieb:

Though you can often get away with ignoring the resistance of a super-
conducting inductor.

even in this case there is resistance, the isolation resistance of the
conductor to ground.

** Hey Uwe,

Bill is Dutch and a colossal pedant.

But you sound like an much bigger, German one.

Show the old fool who is boss.

Go for it - boy.

..... Phil

Bill Sloman
Guest

Fri May 13, 2011 11:55 am

On May 13, 9:29 am, Uwe Hercksen <herck...@mew.uni-erlangen.de> wrote:
Quote:
Joe Snodgrass schrieb:

It seems to go against everything they taught us in class, but the
various turns are closely spaced conductors, separated by a dielectric
layer, just like the plates of a capacitor.  TIA.

Hello,

every real component has all three properties, resistance, inductance
and capacitance. There is no component with only one or two of these
properties.

Though you can often get away with ignoring the resistance of a super-
conducting inductor.

--
Bill Sloman, Nijmegen

John Larkin
Guest

Fri May 13, 2011 3:50 pm

On Fri, 13 May 2011 08:46:27 -0700 (PDT), Bill Sloman
<bill.sloman_at_gmail.com> wrote:

Quote:
On May 13, 12:21 pm, "Phil Allison" <phi...@tpg.com.au> wrote:
"Uwe Hercksen"

BillSlomanschrieb:

Though you can often get away with ignoring the resistance of a super-
conducting inductor.

even in this case there is resistance, the isolation resistance of the
conductor to ground.

** Hey Uwe,

Bill is Dutch and a colossal pedant.

Actually I'm Australian (like Phil, though I don't take any pride in
him as a specimen of the Australian population) even if I'm currently
resident in the Netherlands.

But you sound like an much bigger, German one.

Show the old fool who is boss.

Go for it  -   boy.

Getting a Ph.D. is the kind of thing that instills pedantic habits -
rather than pedantic effect, as someone with a more highly developed
theory of mind than Phil Allison might have been able to detect.

That was comedy?

John

John Larkin
Guest

Fri May 13, 2011 4:35 pm

On Fri, 13 May 2011 09:11:15 -0700 (PDT), Bill Sloman
<bill.sloman_at_ieee.org> wrote:

Quote:
On May 13, 5:50 pm, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Fri, 13 May 2011 08:46:27 -0700 (PDT), Bill Sloman

bill.slo...@gmail.com> wrote:
On May 13, 12:21 pm, "Phil Allison" <phi...@tpg.com.au> wrote:
"Uwe Hercksen"

BillSlomanschrieb:

Though you can often get away with ignoring the resistance of a super-
conducting inductor.

even in this case there is resistance, the isolation resistance of the
conductor to ground.

** Hey Uwe,

Bill is Dutch and a colossal pedant.

Actually I'm Australian (like Phil, though I don't take any pride in
him as a specimen of the Australian population) even if I'm currently
resident in the Netherlands.

But you sound like an much bigger, German one.

Show the old fool who is boss.

Go for it - boy.

Getting a Ph.D. is the kind of thing that instills pedantic habits -
rather than pedantic effect, as someone with a more highly developed
theory of mind than Phil Allison might have been able to detect.

That was comedy?

For those with the right kind of sense of humour - and it helps if you
didn't skip the relevant lectures back when you were an undergraduate.

I doubt there were any lectures on superconductive inductors for me to
miss. And I rarely cut class.

I do work around superconductive magnets, well past \$1e6 and 200
kgauss, in NMR and MRI and FTMS systems. They behave *almost* as
though they have zero resistance. Your statement somehow bypassed my
sense of humor.

lately?

John

Joel Koltner
Guest

Fri May 13, 2011 4:49 pm

"Joe Snodgrass" <joe.snod_at_yahoo.com> wrote in message
Quote:
It seems to go against everything they taught us in class, but the
various turns are closely spaced conductors, separated by a dielectric
layer, just like the plates of a capacitor. TIA.

I don't think it really goes against everything they taught you in class, it's
more like they just might not have ever mentioned it explicitly. :-)

I do recall an exercise in an electromagnetics class where you determined the
capacitance of some coil so as to demonstrate that, at low frequencies, the
positive (inductive) reactance was a couple orders of magnitude higher than
the negative (capacitive) reactiance and hence could be ignored.

As others have mentioned, any arrangement of wires (and perhaps a dielectric)
will have all of resistance, capacitance, and inductance, but the goal is
usually to arrange them in a manner where one of these aspects dominates its
behavior, at least at the "frequencies of interest" where you intend to use
it. Dielectrics do play a large part in this too -- air core inductors are
much more commonly seen than air core capacitors, for instance (although this
is partially due to the fact that magnetic dielectric materials tend to have
non-negligible loss, hysteresis, etc. whereas there are a number of truly
excellent electric dielectric materials available than make for really good
capacitors).

---Joel

Bill Sloman
Guest

Fri May 13, 2011 5:46 pm

On May 13, 12:21 pm, "Phil Allison" <phi...@tpg.com.au> wrote:
Quote:
"Uwe Hercksen"

BillSlomanschrieb:

Though you can often get away with ignoring the resistance of a super-
conducting inductor.

even in this case there is resistance, the isolation resistance of the
conductor to ground.

** Hey Uwe,

Bill is Dutch and a colossal pedant.

Actually I'm Australian (like Phil, though I don't take any pride in
him as a specimen of the Australian population) even if I'm currently
resident in the Netherlands.

Quote:
But you sound like an much bigger, German one.

Show the old fool who is boss.

Go for it  -   boy.

Getting a Ph.D. is the kind of thing that instills pedantic habits -
rather than pedantic effect, as someone with a more highly developed
theory of mind than Phil Allison might have been able to detect.

--
Bill Sloman, Nijmegen

Bill Sloman
Guest

Fri May 13, 2011 6:11 pm

On May 13, 5:50 pm, John Larkin
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
Quote:
On Fri, 13 May 2011 08:46:27 -0700 (PDT), Bill Sloman

bill.slo...@gmail.com> wrote:
On May 13, 12:21 pm, "Phil Allison" <phi...@tpg.com.au> wrote:
"Uwe Hercksen"

BillSlomanschrieb:

Though you can often get away with ignoring the resistance of a super-
conducting inductor.

even in this case there is resistance, the isolation resistance of the
conductor to ground.

** Hey Uwe,

Bill is Dutch and a colossal pedant.

Actually I'm Australian (like Phil, though I don't take any pride in
him as a specimen of the Australian population) even if I'm currently
resident in the Netherlands.

But you sound like an much bigger, German one.

Show the old fool who is boss.

Go for it - boy.

Getting a Ph.D. is the kind of thing that instills pedantic habits -
rather than pedantic effect, as someone with a more highly developed
theory of mind than Phil Allison might have been able to detect.

That was comedy?

For those with the right kind of sense of humour - and it helps if you
didn't skip the relevant lectures back when you were an undergraduate.

--
Bill Sloman, Nijmegen

Phil Hobbs
Guest

Fri May 13, 2011 8:06 pm

Bill Sloman wrote:
Quote:
On May 13, 6:35 pm, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Fri, 13 May 2011 09:11:15 -0700 (PDT),BillSloman

bill.slo...@ieee.org> wrote:
On May 13, 5:50 pm, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Fri, 13 May 2011 08:46:27 -0700 (PDT),BillSloman

bill.slo...@gmail.com> wrote:
On May 13, 12:21 pm, "Phil Allison"<phi...@tpg.com.au> wrote:
"Uwe Hercksen"

BillSlomanschrieb:

Though you can often get away with ignoring the resistance of a super-
conducting inductor.

even in this case there is resistance, the isolation resistance of the
conductor to ground.

** Hey Uwe,

Billis Dutch and a colossal pedant.

Actually I'm Australian (like Phil, though I don't take any pride in
him as a specimen of the Australian population) even if I'm currently
resident in the Netherlands.

But you sound like an much bigger, German one.

Show the old fool who is boss.

Go for it - boy.

Getting a Ph.D. is the kind of thing that instills pedantic habits -
rather than pedantic effect, as someone with a more highly developed
theory of mind than Phil Allison might have been able to detect.

That was comedy?

For those with the right kind of sense of humour - and it helps if you
didn't skip the relevant lectures back when you were an undergraduate.

I doubt there were any lectures on superconductive inductors for me to
miss. And I rarely cut class.

I do work around superconductive magnets, well past \$1e6 and 200
kgauss, in NMR and MRI and FTMS systems. They behave *almost* as
though they have zero resistance. Your statement somehow bypassed my
sense of humor.

lately?

No. Did have an interesting conversation with a couple of guys at an
Analog Devices presentation earlier in the week - they are developing
an infra-red sensing array which basically runs on the edge of super-
conduction, with super-conducting quantum interference devices to
amplify the sensor output. The whole thing is going into a satellite
with a closed-circuit liquid helium refrigeration system.

I was deeply envious.

--
Bill Sloman, Nijmegen

Superconducting bolometers are pretty amazing. At IBM a colleague of
mine had an FTIR spectrometer with one of those in it--it was better
than any available photodiode in the 3-5 um region.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal
ElectroOptical Innovations
55 Orchard Rd
Briarcliff Manor NY 10510
845-480-2058

email: hobbs (atsign) electrooptical (period) net
http://electrooptical.net

Bill Sloman
Guest

Fri May 13, 2011 9:04 pm

On May 13, 6:35 pm, John Larkin
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
Quote:
On Fri, 13 May 2011 09:11:15 -0700 (PDT),BillSloman

bill.slo...@ieee.org> wrote:
On May 13, 5:50 pm, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Fri, 13 May 2011 08:46:27 -0700 (PDT),BillSloman

bill.slo...@gmail.com> wrote:
On May 13, 12:21 pm, "Phil Allison" <phi...@tpg.com.au> wrote:
"Uwe Hercksen"

BillSlomanschrieb:

Though you can often get away with ignoring the resistance of a super-
conducting inductor.

even in this case there is resistance, the isolation resistance of the
conductor to ground.

** Hey Uwe,

Billis Dutch and a colossal pedant.

Actually I'm Australian (like Phil, though I don't take any pride in
him as a specimen of the Australian population) even if I'm currently
resident in the Netherlands.

But you sound like an much bigger, German one.

Show the old fool who is boss.

Go for it - boy.

Getting a Ph.D. is the kind of thing that instills pedantic habits -
rather than pedantic effect, as someone with a more highly developed
theory of mind than Phil Allison might have been able to detect.

That was comedy?

For those with the right kind of sense of humour - and it helps if you
didn't skip the relevant lectures back when you were an undergraduate.

I doubt there were any lectures on superconductive inductors for me to
miss. And I rarely cut class.

I do work around superconductive magnets, well past \$1e6 and 200
kgauss, in NMR and MRI and FTMS systems. They behave *almost* as
though they have zero resistance. Your statement somehow bypassed my
sense of humor.

lately?

No. Did have an interesting conversation with a couple of guys at an
Analog Devices presentation earlier in the week - they are developing
an infra-red sensing array which basically runs on the edge of super-
conduction, with super-conducting quantum interference devices to
amplify the sensor output. The whole thing is going into a satellite
with a closed-circuit liquid helium refrigeration system.

I was deeply envious.

--
Bill Sloman, Nijmegen

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