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capacitor COE question
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John Larkin
Oct 26, 2012, 11:32:18 AM10/26/12
to
If a capacitor has a largish temperature coefficient (hundreds of PPM
capacitance change per degree C maybe), what happens to a charged cap
when the temperature changes? Presumably C*V stays constant, so the
stored energy 0.5*C*V^2 changes.
So, would the specific heat of the capacitor be different, as a
function of whether it is charged or not?
--
John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com
Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Photonics and fiberoptic TTL data links
VME analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators
George Herold
Oct 26, 2012, 11:54:34 AM10/26/12
to
On Oct 26, 11:32 am, John Larkin
capacity of the cap is about 1 J/(gram-K) What's the Q^2/C energy
change? (for 0.1uF and 10 V looks like only ~10uJ's of total energy)
George H.
>
> --
>
> John Larkin Highland Technology Incwww.highlandtechnology.com jlarkin at highlandtechnology dot com
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
> If a capacitor has a largish temperature coefficient (hundreds of PPM
> capacitance change per degree C maybe), what happens to a charged cap
> when the temperature changes? Presumably C*V stays constant, so the
> stored energy 0.5*C*V^2 changes.
>
> So, would the specific heat of the capacitor be different, as a
> function of whether it is charged or not?
Fun! Sure why not. But could you measure it? Assume the heat
> If a capacitor has a largish temperature coefficient (hundreds of PPM
> capacitance change per degree C maybe), what happens to a charged cap
> when the temperature changes? Presumably C*V stays constant, so the
> stored energy 0.5*C*V^2 changes.
>
> So, would the specific heat of the capacitor be different, as a
> function of whether it is charged or not?
capacity of the cap is about 1 J/(gram-K) What's the Q^2/C energy
change? (for 0.1uF and 10 V looks like only ~10uJ's of total energy)
George H.
>
> --
>
> John Larkin Highland Technology Incwww.highlandtechnology.com jlarkin at highlandtechnology dot com
Spehro Pefhany
Oct 26, 2012, 12:01:40 PM10/26/12
to
On Fri, 26 Oct 2012 08:32:18 -0700, John Larkin
<jjla...@highNOTlandTHIStechnologyPART.com> wrote:
>
>
>If a capacitor has a largish temperature coefficient (hundreds of PPM
>capacitance change per degree C maybe), what happens to a charged cap
>when the temperature changes? Presumably C*V stays constant, so the
>stored energy 0.5*C*V^2 changes.
>
>So, would the specific heat of the capacitor be different, as a
>function of whether it is charged or not?
Yes, the heat capacity is going to depend on the charge. Can't be
<jjla...@highNOTlandTHIStechnologyPART.com> wrote:
>
>
>If a capacitor has a largish temperature coefficient (hundreds of PPM
>capacitance change per degree C maybe), what happens to a charged cap
>when the temperature changes? Presumably C*V stays constant, so the
>stored energy 0.5*C*V^2 changes.
>
>So, would the specific heat of the capacitor be different, as a
>function of whether it is charged or not?
otherwise.
JOF
Oct 26, 2012, 12:09:04 PM10/26/12
to
On Fri, 26 Oct 2012 08:32:18 -0700, John Larkin
<jjla...@highNOTlandTHIStechnologyPART.com> wrote:
>
>
<jjla...@highNOTlandTHIStechnologyPART.com> wrote:
>
>
>If a capacitor has a largish temperature coefficient (hundreds of PPM
>capacitance change per degree C maybe), what happens to a charged cap
>when the temperature changes? Presumably C*V stays constant, so the
>stored energy 0.5*C*V^2 changes.
That does not compute. If the capacitance changes, and the charge does
>capacitance change per degree C maybe), what happens to a charged cap
>when the temperature changes? Presumably C*V stays constant, so the
>stored energy 0.5*C*V^2 changes.
not, the voltage must change inversely, keeping the stored electrical
energy constant.
Helmut Wabnig
Oct 26, 2012, 12:05:24 PM10/26/12
to
On Fri, 26 Oct 2012 08:32:18 -0700, John Larkin
<jjla...@highNOTlandTHIStechnologyPART.com> wrote:
>
>
<jjla...@highNOTlandTHIStechnologyPART.com> wrote:
>
>
>If a capacitor has a largish temperature coefficient (hundreds of PPM
>capacitance change per degree C maybe), what happens to a charged cap
>when the temperature changes? Presumably C*V stays constant, so the
>stored energy 0.5*C*V^2 changes.
Why should C*V be constant?
>capacitance change per degree C maybe), what happens to a charged cap
>when the temperature changes? Presumably C*V stays constant, so the
>stored energy 0.5*C*V^2 changes.
w.
John Larkin
Oct 26, 2012, 12:18:14 PM10/26/12
to
measurable for a real capacitor.
Thinking about this, for no good reason, I tripped across this site:
http://www.electronics-cooling.com/2012/09/thermal-facts-fairy-tales-the-temperature-dependence-of-the-specific-heat/
Big Dog
Oct 26, 2012, 12:24:15 PM10/26/12
to
On 10/26/2012 11:09 AM, JOF wrote:
> On Fri, 26 Oct 2012 08:32:18 -0700, John Larkin
> <jjla...@highNOTlandTHIStechnologyPART.com> wrote:
>
>>
>>
>> If a capacitor has a largish temperature coefficient (hundreds of PPM
>> capacitance change per degree C maybe), what happens to a charged cap
>> when the temperature changes? Presumably C*V stays constant, so the
>> stored energy 0.5*C*V^2 changes.
>
> That does not compute. If the capacitance changes, and the charge does
> not, the voltage must change inversely, keeping the stored electrical
> energy constant.
No, OP was right, and it's a cute question.
> On Fri, 26 Oct 2012 08:32:18 -0700, John Larkin
> <jjla...@highNOTlandTHIStechnologyPART.com> wrote:
>
>>
>>
>> If a capacitor has a largish temperature coefficient (hundreds of PPM
>> capacitance change per degree C maybe), what happens to a charged cap
>> when the temperature changes? Presumably C*V stays constant, so the
>> stored energy 0.5*C*V^2 changes.
>
> That does not compute. If the capacitance changes, and the charge does
> not, the voltage must change inversely, keeping the stored electrical
> energy constant.
Stored energy is proportional to C and V^2, so even if V is inversely
proportional to C, then the energy will change.
A simpler way of putting it is that CV=Q will be constant (if the
capacitor is isolated) and the energy is proportional to Q^2/C, which
obviously changes.
John Larkin
Oct 26, 2012, 12:24:16 PM10/26/12
to
On Fri, 26 Oct 2012 11:09:04 -0500, JOF <qu...@yahoo.com> wrote:
>On Fri, 26 Oct 2012 08:32:18 -0700, John Larkin
><jjla...@highNOTlandTHIStechnologyPART.com> wrote:
>
>>
>>
>>If a capacitor has a largish temperature coefficient (hundreds of PPM
>>capacitance change per degree C maybe), what happens to a charged cap
>>when the temperature changes? Presumably C*V stays constant, so the
>>stored energy 0.5*C*V^2 changes.
>
>That does not compute. If the capacitance changes, and the charge does
>not, the voltage must change inversely, keeping the stored electrical
>energy constant.
>
1 farad, 1 volt, 0.5 joules
>On Fri, 26 Oct 2012 08:32:18 -0700, John Larkin
><jjla...@highNOTlandTHIStechnologyPART.com> wrote:
>
>>
>>
>>If a capacitor has a largish temperature coefficient (hundreds of PPM
>>capacitance change per degree C maybe), what happens to a charged cap
>>when the temperature changes? Presumably C*V stays constant, so the
>>stored energy 0.5*C*V^2 changes.
>
>That does not compute. If the capacitance changes, and the charge does
>not, the voltage must change inversely, keeping the stored electrical
>energy constant.
>
0.5 farad, 2 volts, 1 joule.
Same charge, different energies.
Spehro Pefhany
Oct 26, 2012, 12:31:10 PM10/26/12
to
On Fri, 26 Oct 2012 18:05:24 +0200, Helmut Wabnig <hwabnig@.- ---
-.dotat> wrote:
>On Fri, 26 Oct 2012 08:32:18 -0700, John Larkin
><jjla...@highNOTlandTHIStechnologyPART.com> wrote:
>
>>
>>
>>If a capacitor has a largish temperature coefficient (hundreds of PPM
>>capacitance change per degree C maybe), what happens to a charged cap
>>when the temperature changes? Presumably C*V stays constant, so the
>>stored energy 0.5*C*V^2 changes.
>
>
>Why should C*V be constant?
>w.
Assuming no leakage, Q should be constant.
-.dotat> wrote:
>On Fri, 26 Oct 2012 08:32:18 -0700, John Larkin
><jjla...@highNOTlandTHIStechnologyPART.com> wrote:
>
>>
>>
>>If a capacitor has a largish temperature coefficient (hundreds of PPM
>>capacitance change per degree C maybe), what happens to a charged cap
>>when the temperature changes? Presumably C*V stays constant, so the
>>stored energy 0.5*C*V^2 changes.
>
>
>Why should C*V be constant?
>w.
JOF
Oct 26, 2012, 12:31:10 PM10/26/12
to
On Fri, 26 Oct 2012 09:24:16 -0700, John Larkin
--
John
<jjla...@highNOTlandTHIStechnologyPART.com> wrote:
>On Fri, 26 Oct 2012 11:09:04 -0500, JOF <qu...@yahoo.com> wrote:
>
>>On Fri, 26 Oct 2012 08:32:18 -0700, John Larkin
>><jjla...@highNOTlandTHIStechnologyPART.com> wrote:
>>
>>>
>>>
>>>If a capacitor has a largish temperature coefficient (hundreds of PPM
>>>capacitance change per degree C maybe), what happens to a charged cap
>>>when the temperature changes? Presumably C*V stays constant, so the
>>>stored energy 0.5*C*V^2 changes.
>>
>>That does not compute. If the capacitance changes, and the charge does
>>not, the voltage must change inversely, keeping the stored electrical
>>energy constant.
>>
>
>
>1 farad, 1 volt, 0.5 joules
>
>0.5 farad, 2 volts, 1 joule.
>
>Same charge, different energies.
Ok, I see it now.
>On Fri, 26 Oct 2012 11:09:04 -0500, JOF <qu...@yahoo.com> wrote:
>
>>On Fri, 26 Oct 2012 08:32:18 -0700, John Larkin
>><jjla...@highNOTlandTHIStechnologyPART.com> wrote:
>>
>>>
>>>
>>>If a capacitor has a largish temperature coefficient (hundreds of PPM
>>>capacitance change per degree C maybe), what happens to a charged cap
>>>when the temperature changes? Presumably C*V stays constant, so the
>>>stored energy 0.5*C*V^2 changes.
>>
>>That does not compute. If the capacitance changes, and the charge does
>>not, the voltage must change inversely, keeping the stored electrical
>>energy constant.
>>
>
>
>1 farad, 1 volt, 0.5 joules
>
>0.5 farad, 2 volts, 1 joule.
>
>Same charge, different energies.
--
John
Spehro Pefhany
Oct 26, 2012, 12:38:42 PM10/26/12
to
On Fri, 26 Oct 2012 09:18:14 -0700, John Larkin
"interesting" things at very low temperatures.
<jjla...@highNOTlandTHIStechnologyPART.com> wrote:
>On Fri, 26 Oct 2012 12:01:40 -0400, Spehro Pefhany
><spef...@interlogDOTyou.knowwhat> wrote:
>
>>On Fri, 26 Oct 2012 08:32:18 -0700, John Larkin
>><jjla...@highNOTlandTHIStechnologyPART.com> wrote:
>>
>>>
>>>
>>>If a capacitor has a largish temperature coefficient (hundreds of PPM
>>>capacitance change per degree C maybe), what happens to a charged cap
>>>when the temperature changes? Presumably C*V stays constant, so the
>>>stored energy 0.5*C*V^2 changes.
>>>
>>>So, would the specific heat of the capacitor be different, as a
>>>function of whether it is charged or not?
>>
>>Yes, the heat capacity is going to depend on the charge. Can't be
>>otherwise.
>>
>
>Yeah, I thought so. But as George says, it wouldn't be easily
>measurable for a real capacitor.
>
>Thinking about this, for no good reason, I tripped across this site:
>
>http://www.electronics-cooling.com/2012/09/thermal-facts-fairy-tales-the-temperature-dependence-of-the-specific-heat/
Specific heat and thermal conductivity start to do really
>On Fri, 26 Oct 2012 12:01:40 -0400, Spehro Pefhany
><spef...@interlogDOTyou.knowwhat> wrote:
>
>>On Fri, 26 Oct 2012 08:32:18 -0700, John Larkin
>><jjla...@highNOTlandTHIStechnologyPART.com> wrote:
>>
>>>
>>>
>>>If a capacitor has a largish temperature coefficient (hundreds of PPM
>>>capacitance change per degree C maybe), what happens to a charged cap
>>>when the temperature changes? Presumably C*V stays constant, so the
>>>stored energy 0.5*C*V^2 changes.
>>>
>>>So, would the specific heat of the capacitor be different, as a
>>>function of whether it is charged or not?
>>
>>Yes, the heat capacity is going to depend on the charge. Can't be
>>otherwise.
>>
>
>Yeah, I thought so. But as George says, it wouldn't be easily
>measurable for a real capacitor.
>
>Thinking about this, for no good reason, I tripped across this site:
>
>http://www.electronics-cooling.com/2012/09/thermal-facts-fairy-tales-the-temperature-dependence-of-the-specific-heat/
"interesting" things at very low temperatures.
Syd Rumpo
Oct 26, 2012, 12:41:02 PM10/26/12
to
On 26/10/2012 17:24, John Larkin wrote:
> On Fri, 26 Oct 2012 11:09:04 -0500, JOF <qu...@yahoo.com> wrote:
>
>> On Fri, 26 Oct 2012 08:32:18 -0700, John Larkin
>> <jjla...@highNOTlandTHIStechnologyPART.com> wrote:
>>
>>>
>>>
>>> If a capacitor has a largish temperature coefficient (hundreds of PPM
>>> capacitance change per degree C maybe), what happens to a charged cap
>>> when the temperature changes? Presumably C*V stays constant, so the
>>> stored energy 0.5*C*V^2 changes.
>>
>> That does not compute. If the capacitance changes, and the charge does
>> not, the voltage must change inversely, keeping the stored electrical
>> energy constant.
>>
>
>
> 1 farad, 1 volt, 0.5 joules
>
> 0.5 farad, 2 volts, 1 joule.
>
> Same charge, different energies.
Yes, the charges are now further apart due to thermal expansion. Moving
> On Fri, 26 Oct 2012 11:09:04 -0500, JOF <qu...@yahoo.com> wrote:
>
>> On Fri, 26 Oct 2012 08:32:18 -0700, John Larkin
>> <jjla...@highNOTlandTHIStechnologyPART.com> wrote:
>>
>>>
>>>
>>> If a capacitor has a largish temperature coefficient (hundreds of PPM
>>> capacitance change per degree C maybe), what happens to a charged cap
>>> when the temperature changes? Presumably C*V stays constant, so the
>>> stored energy 0.5*C*V^2 changes.
>>
>> That does not compute. If the capacitance changes, and the charge does
>> not, the voltage must change inversely, keeping the stored electrical
>> energy constant.
>>
>
>
> 1 farad, 1 volt, 0.5 joules
>
> 0.5 farad, 2 volts, 1 joule.
>
> Same charge, different energies.
them further apart added some energy.
Probably.
In (say) a parallel plate air-gap capacitor, the plates will bend
towards each other slightly as charge is added. Is the electrical
energy stored the same as the mechanical energy which would be required
to bend the uncharged plates by the same amount?
Cheers
--
Syd
Phil Hobbs
Oct 26, 2012, 12:43:24 PM10/26/12
to
On 10/26/2012 11:32 AM, John Larkin wrote:
>
>
> If a capacitor has a largish temperature coefficient (hundreds of PPM
> capacitance change per degree C maybe), what happens to a charged cap
> when the temperature changes? Presumably C*V stays constant, so the
> stored energy 0.5*C*V^2 changes.
>
> So, would the specific heat of the capacitor be different, as a
> function of whether it is charged or not?
>
>
Yup. Work has to be done on the stored charge, just as you say. Of
>
>
> If a capacitor has a largish temperature coefficient (hundreds of PPM
> capacitance change per degree C maybe), what happens to a charged cap
> when the temperature changes? Presumably C*V stays constant, so the
> stored energy 0.5*C*V^2 changes.
>
> So, would the specific heat of the capacitor be different, as a
> function of whether it is charged or not?
>
>
course it might not be exactly V*delta_C as you'd expect, because the
voltage coefficient might change with temperature too, and the energy is
actually the integral of CV*dV.
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics
160 North State Road #203
Briarcliff Manor NY 10510
hobbs at electrooptical dot net
http://electrooptical.net
Phil Hobbs
Oct 26, 2012, 12:50:42 PM10/26/12
to
On 10/26/2012 12:18 PM, John Larkin wrote:
> On Fri, 26 Oct 2012 12:01:40 -0400, Spehro Pefhany
> <spef...@interlogDOTyou.knowwhat> wrote:
>
>> On Fri, 26 Oct 2012 08:32:18 -0700, John Larkin
>> <jjla...@highNOTlandTHIStechnologyPART.com> wrote:
>>
>>>
>>>
>>> If a capacitor has a largish temperature coefficient (hundreds of PPM
>>> capacitance change per degree C maybe), what happens to a charged cap
>>> when the temperature changes? Presumably C*V stays constant, so the
>>> stored energy 0.5*C*V^2 changes.
>>>
>>> So, would the specific heat of the capacitor be different, as a
>>> function of whether it is charged or not?
>>
>> Yes, the heat capacity is going to depend on the charge. Can't be
>> otherwise.
>>
>
> Yeah, I thought so. But as George says, it wouldn't be easily
> measurable for a real capacitor.
>
> Thinking about this, for no good reason, I tripped across this site:
>
> http://www.electronics-cooling.com/2012/09/thermal-facts-fairy-tales-the-temperature-dependence-of-the-specific-heat/
>
>
Phase transitions do make life more interesting, but as the article
> On Fri, 26 Oct 2012 12:01:40 -0400, Spehro Pefhany
> <spef...@interlogDOTyou.knowwhat> wrote:
>
>> On Fri, 26 Oct 2012 08:32:18 -0700, John Larkin
>> <jjla...@highNOTlandTHIStechnologyPART.com> wrote:
>>
>>>
>>>
>>> If a capacitor has a largish temperature coefficient (hundreds of PPM
>>> capacitance change per degree C maybe), what happens to a charged cap
>>> when the temperature changes? Presumably C*V stays constant, so the
>>> stored energy 0.5*C*V^2 changes.
>>>
>>> So, would the specific heat of the capacitor be different, as a
>>> function of whether it is charged or not?
>>
>> Yes, the heat capacity is going to depend on the charge. Can't be
>> otherwise.
>>
>
> Yeah, I thought so. But as George says, it wouldn't be easily
> measurable for a real capacitor.
>
> Thinking about this, for no good reason, I tripped across this site:
>
> http://www.electronics-cooling.com/2012/09/thermal-facts-fairy-tales-the-temperature-dependence-of-the-specific-heat/
>
>
says, in the temperature vs internal energy curve, it's just a flat spot
and not a big fat discontinuity. That would be pretty simple to model
in SPICE, I should think--just a constant times a Boolean added to the
charge on a capacitor, or something like that.
The same issue exists in thermal conduction, but is much more serious,
especially at low temperature--the Lakeshore Cryogenics catalogue has
tables of "Thermal conductivity integral" because you won't get anything
like the right answer otherwise.
http://www.lakeshore.com/Documents/LSTC_appendixI_l.pdf
George Herold
Oct 26, 2012, 1:01:15 PM10/26/12
to
On Oct 26, 12:18 pm, John Larkin
>
> --
>
> John Larkin Highland Technology Incwww.highlandtechnology.com jlarkin at highlandtechnology dot com
>
> - Show quoted text -
Ouuu I like that graph! (figure 1.) I'll have to order some poly-
propelene and poly-ethylene. I wonder what the phase change is?
Maybe the dielectric constant changes too?
The interesting (physics-wise) way to compare materials is by the
molar heat capacity. (Water is amazing in that regard.)
George H.
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
> On Fri, 26 Oct 2012 12:01:40 -0400, Spehro Pefhany
>
>
>
>
>
> <speffS...@interlogDOTyou.knowwhat> wrote:
> >On Fri, 26 Oct 2012 08:32:18 -0700, John Larkin
> ><jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
>
> >>If a capacitor has a largish temperature coefficient (hundreds of PPM
> >>capacitance change per degree C maybe), what happens to a charged cap
> >>when the temperature changes? Presumably C*V stays constant, so the
> >>stored energy 0.5*C*V^2 changes.
>
> >>So, would the specific heat of the capacitor be different, as a
> >>function of whether it is charged or not?
>
> >Yes, the heat capacity is going to depend on the charge. Can't be
> >otherwise.
>
> Yeah, I thought so. But as George says, it wouldn't be easily
> measurable for a real capacitor.
>
> Thinking about this, for no good reason, I tripped across this site:
>
> http://www.electronics-cooling.com/2012/09/thermal-facts-fairy-tales-...
> On Fri, 26 Oct 2012 12:01:40 -0400, Spehro Pefhany
>
>
>
>
>
> <speffS...@interlogDOTyou.knowwhat> wrote:
> >On Fri, 26 Oct 2012 08:32:18 -0700, John Larkin
> ><jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
>
> >>If a capacitor has a largish temperature coefficient (hundreds of PPM
> >>capacitance change per degree C maybe), what happens to a charged cap
> >>when the temperature changes? Presumably C*V stays constant, so the
> >>stored energy 0.5*C*V^2 changes.
>
> >>So, would the specific heat of the capacitor be different, as a
> >>function of whether it is charged or not?
>
> >Yes, the heat capacity is going to depend on the charge. Can't be
> >otherwise.
>
> Yeah, I thought so. But as George says, it wouldn't be easily
> measurable for a real capacitor.
>
> Thinking about this, for no good reason, I tripped across this site:
>
>
> --
>
> John Larkin Highland Technology Incwww.highlandtechnology.com jlarkin at highlandtechnology dot com
>
> Precision electronic instrumentation
> Picosecond-resolution Digital Delay and Pulse generators
> Custom timing and laser controllers
> Photonics and fiberoptic TTL data links
> VME analog, thermocouple, LVDT, synchro, tachometer
> Multichannel arbitrary waveform generators- Hide quoted text -
> Precision electronic instrumentation
> Picosecond-resolution Digital Delay and Pulse generators
> Custom timing and laser controllers
> Photonics and fiberoptic TTL data links
> VME analog, thermocouple, LVDT, synchro, tachometer
>
> - Show quoted text -
Ouuu I like that graph! (figure 1.) I'll have to order some poly-
propelene and poly-ethylene. I wonder what the phase change is?
Maybe the dielectric constant changes too?
The interesting (physics-wise) way to compare materials is by the
molar heat capacity. (Water is amazing in that regard.)
George H.
Phil Hobbs
Oct 26, 2012, 1:13:43 PM10/26/12
to
On 10/26/2012 01:01 PM, George Herold wrote:
> On Oct 26, 12:18 pm, John Larkin
> <jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
>> On Fri, 26 Oct 2012 12:01:40 -0400, Spehro Pefhany
>>
>>
>>
>>
>>
>> <speffS...@interlogDOTyou.knowwhat> wrote:
>>> On Fri, 26 Oct 2012 08:32:18 -0700, John Larkin
>>> <jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
>>
>>>> If a capacitor has a largish temperature coefficient (hundreds of PPM
>>>> capacitance change per degree C maybe), what happens to a charged cap
>>>> when the temperature changes? Presumably C*V stays constant, so the
>>>> stored energy 0.5*C*V^2 changes.
>>
>>>> So, would the specific heat of the capacitor be different, as a
>>>> function of whether it is charged or not?
>>
>>> Yes, the heat capacity is going to depend on the charge. Can't be
>>> otherwise.
>>
>> Yeah, I thought so. But as George says, it wouldn't be easily
>> measurable for a real capacitor.
>>
>> Thinking about this, for no good reason, I tripped across this site:
>>
>> http://www.electronics-cooling.com/2012/09/thermal-facts-fairy-tales-...
>>
>> --
>>
>> John Larkin
>
> On Oct 26, 12:18 pm, John Larkin
> <jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
>> On Fri, 26 Oct 2012 12:01:40 -0400, Spehro Pefhany
>>
>>
>>
>>
>>
>> <speffS...@interlogDOTyou.knowwhat> wrote:
>>> On Fri, 26 Oct 2012 08:32:18 -0700, John Larkin
>>> <jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
>>
>>>> If a capacitor has a largish temperature coefficient (hundreds of PPM
>>>> capacitance change per degree C maybe), what happens to a charged cap
>>>> when the temperature changes? Presumably C*V stays constant, so the
>>>> stored energy 0.5*C*V^2 changes.
>>
>>>> So, would the specific heat of the capacitor be different, as a
>>>> function of whether it is charged or not?
>>
>>> Yes, the heat capacity is going to depend on the charge. Can't be
>>> otherwise.
>>
>> Yeah, I thought so. But as George says, it wouldn't be easily
>> measurable for a real capacitor.
>>
>> Thinking about this, for no good reason, I tripped across this site:
>>
>> http://www.electronics-cooling.com/2012/09/thermal-facts-fairy-tales-...
>>
>> --
>>
>> John Larkin
>
> Ouuu I like that graph! (figure 1.) I'll have to order some poly-
> propelene and poly-ethylene. I wonder what the phase change is?
> Maybe the dielectric constant changes too?
>
> The interesting (physics-wise) way to compare materials is by the
> molar heat capacity. (Water is amazing in that regard.)
>
> George H.
Glass transition point. Teflon's is exciting too--the CTE changes by
> propelene and poly-ethylene. I wonder what the phase change is?
> Maybe the dielectric constant changes too?
>
> The interesting (physics-wise) way to compare materials is by the
> molar heat capacity. (Water is amazing in that regard.)
>
> George H.
like a factor of 10. There are some cool graphs here:
http://www.netzsch-thermal-analysis.com/download/P-022_315.pdf .
Modelling the thermal energy looks like a good application for one of
JT's fave tanh functions.
Helmut Wabnig
Oct 26, 2012, 1:14:42 PM10/26/12
to
Wanted to point to the "capacitor paradoxon"
when an uncharged cap is switched parallel to a charged cap.
But you know anyway.
w.
John Larkin
Oct 26, 2012, 1:21:11 PM10/26/12
to
On Fri, 26 Oct 2012 17:41:02 +0100, Syd Rumpo <use...@nononono.co.uk>
wrote:
If the plates were perfectly rigid, you'd still store the electrical
energy.
If you pull the plates of a vacuum pp capacitor apart, you do work on
it, like stretching a spring. CV is conserved, but C goes down and V
goes up, so the work you did pulling the plates farther apart is
stored as electrical energy, 0.5*C*V^2. Like a spring, you can get
that mechanical energy back later.
Unfortunately, the temperature coefficient of vacuum is zero (I
think!) so it's not a useful analogy to illustrate my case.
--
John Larkin Highland Technology, Inc
jlarkin at highlandtechnology dot com
http://www.highlandtechnology.com
Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom laser drivers and controllers
wrote:
energy.
If you pull the plates of a vacuum pp capacitor apart, you do work on
it, like stretching a spring. CV is conserved, but C goes down and V
goes up, so the work you did pulling the plates farther apart is
stored as electrical energy, 0.5*C*V^2. Like a spring, you can get
that mechanical energy back later.
Unfortunately, the temperature coefficient of vacuum is zero (I
think!) so it's not a useful analogy to illustrate my case.
--
John Larkin Highland Technology, Inc
jlarkin at highlandtechnology dot com
Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Photonics and fiberoptic TTL data links
VME thermocouple, LVDT, synchro acquisition and simulation
Phil Hobbs
Oct 26, 2012, 1:29:14 PM10/26/12
to
built what he called "capacitive muscle", using oil inside bags made of
flex circuit material, using that effect. (When it's the material that
moves, its fancy name is "dielectrophoresis".)
Syd Rumpo
Oct 26, 2012, 1:39:28 PM10/26/12
to
for the same force.
<snip>
Cheers
--
Syd
John Larkin
Oct 26, 2012, 2:00:43 PM10/26/12
to
On Fri, 26 Oct 2012 19:14:42 +0200, Helmut Wabnig <hwabnig@.- ---
--
John Larkin Highland Technology, Inc
Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom laser drivers and controllers
-.dotat> wrote:
>On Fri, 26 Oct 2012 12:31:10 -0400, Spehro Pefhany
><spef...@interlogDOTyou.knowwhat> wrote:
>
>>On Fri, 26 Oct 2012 18:05:24 +0200, Helmut Wabnig <hwabnig@.- ---
>>-.dotat> wrote:
>>
>>>On Fri, 26 Oct 2012 08:32:18 -0700, John Larkin
>>><jjla...@highNOTlandTHIStechnologyPART.com> wrote:
>>>
>>>>
>>>>
>>>>If a capacitor has a largish temperature coefficient (hundreds of PPM
>>>>capacitance change per degree C maybe), what happens to a charged cap
>>>>when the temperature changes? Presumably C*V stays constant, so the
>>>>stored energy 0.5*C*V^2 changes.
>>>
>>>
>>>Why should C*V be constant?
>>>w.
>>
>>Assuming no leakage, Q should be constant.
>
>Yep. Distraction.
>
>Wanted to point to the "capacitor paradoxon"
>when an uncharged cap is switched parallel to a charged cap.
>But you know anyway.
>
>w.
This group (s.e.d.) has done that one to death.
>On Fri, 26 Oct 2012 12:31:10 -0400, Spehro Pefhany
><spef...@interlogDOTyou.knowwhat> wrote:
>
>>On Fri, 26 Oct 2012 18:05:24 +0200, Helmut Wabnig <hwabnig@.- ---
>>-.dotat> wrote:
>>
>>>On Fri, 26 Oct 2012 08:32:18 -0700, John Larkin
>>><jjla...@highNOTlandTHIStechnologyPART.com> wrote:
>>>
>>>>
>>>>
>>>>If a capacitor has a largish temperature coefficient (hundreds of PPM
>>>>capacitance change per degree C maybe), what happens to a charged cap
>>>>when the temperature changes? Presumably C*V stays constant, so the
>>>>stored energy 0.5*C*V^2 changes.
>>>
>>>
>>>Why should C*V be constant?
>>>w.
>>
>>Assuming no leakage, Q should be constant.
>
>Yep. Distraction.
>
>Wanted to point to the "capacitor paradoxon"
>when an uncharged cap is switched parallel to a charged cap.
>But you know anyway.
>
>w.
--
John Larkin Highland Technology, Inc
jlarkin at highlandtechnology dot com
http://www.highlandtechnology.com
Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Photonics and fiberoptic TTL data links
John Larkin
Oct 26, 2012, 2:03:48 PM10/26/12
to
On Fri, 26 Oct 2012 18:05:24 +0200, Helmut Wabnig <hwabnig@.- ---
-.dotat> wrote:
-.dotat> wrote:
>On Fri, 26 Oct 2012 08:32:18 -0700, John Larkin
><jjla...@highNOTlandTHIStechnologyPART.com> wrote:
>
>>
>>
>>If a capacitor has a largish temperature coefficient (hundreds of PPM
>>capacitance change per degree C maybe), what happens to a charged cap
>>when the temperature changes? Presumably C*V stays constant, so the
>>stored energy 0.5*C*V^2 changes.
>
>
>Why should C*V be constant?
>w.
>
>
Actually, for a real dielectric, I can't swear that it is.
><jjla...@highNOTlandTHIStechnologyPART.com> wrote:
>
>>
>>
>>If a capacitor has a largish temperature coefficient (hundreds of PPM
>>capacitance change per degree C maybe), what happens to a charged cap
>>when the temperature changes? Presumably C*V stays constant, so the
>>stored energy 0.5*C*V^2 changes.
>
>
>Why should C*V be constant?
>w.
>
>
--
John Larkin Highland Technology, Inc
jlarkin at highlandtechnology dot com
http://www.highlandtechnology.com
Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Photonics and fiberoptic TTL data links
Larry Stones
Oct 26, 2012, 2:17:48 PM10/26/12
to
On Fri, 26 Oct 2012 11:24:15 -0500, Big Dog wrote:
> On 10/26/2012 11:09 AM, JOF wrote:
>> On Fri, 26 Oct 2012 08:32:18 -0700, John Larkin
>> <jjla...@highNOTlandTHIStechnologyPART.com> wrote:
>>
>>
>>>
>>> If a capacitor has a largish temperature coefficient (hundreds of PPM
>>> capacitance change per degree C maybe), what happens to a charged cap
>>> when the temperature changes? Presumably C*V stays constant, so the
>>> stored energy 0.5*C*V^2 changes.
>>
>> That does not compute. If the capacitance changes, and the charge does
>> not, the voltage must change inversely, keeping the stored electrical
>> energy constant.
>
> No, OP was right, and it's a cute question.
> Stored energy is proportional to C and V^2, so even if V is inversely
> proportional to C, then the energy will change.
Where will this energy go?
> On 10/26/2012 11:09 AM, JOF wrote:
>> On Fri, 26 Oct 2012 08:32:18 -0700, John Larkin
>> <jjla...@highNOTlandTHIStechnologyPART.com> wrote:
>>
>>
>>>
>>> If a capacitor has a largish temperature coefficient (hundreds of PPM
>>> capacitance change per degree C maybe), what happens to a charged cap
>>> when the temperature changes? Presumably C*V stays constant, so the
>>> stored energy 0.5*C*V^2 changes.
>>
>> That does not compute. If the capacitance changes, and the charge does
>> not, the voltage must change inversely, keeping the stored electrical
>> energy constant.
>
> No, OP was right, and it's a cute question.
> Stored energy is proportional to C and V^2, so even if V is inversely
> proportional to C, then the energy will change.
George Herold
Oct 26, 2012, 2:33:08 PM10/26/12
to
On Oct 26, 1:13 pm, Phil Hobbs
Ahh, OK I think I heard about that in teflon.
Googling (polyethylene heat capacity)
I find this (long link) from NIST.
http://www.google.com/url?sa=t&rct=j&q=&esrc=s&frm=1&source=web&cd=1&cad=rja&ved=0CB4QFjAA&url=http%3A%2F%2Fwww.nist.gov%2Fdata%2FPDFfiles%2Fjpcrd178.pdf&ei=4dSKUN_7B6bp0gGukYGIBQ&usg=AFQjCNHHlzQ68WY1xuiuUPeWLhnvdFK7lA&sig2=e48S2mun--0BBoqewAqlFw
Scrolling down to near the bottom (pages 27 and 30) I see no nice
bumps in the heat capacity.
George H.
Googling (polyethylene heat capacity)
I find this (long link) from NIST.
http://www.google.com/url?sa=t&rct=j&q=&esrc=s&frm=1&source=web&cd=1&cad=rja&ved=0CB4QFjAA&url=http%3A%2F%2Fwww.nist.gov%2Fdata%2FPDFfiles%2Fjpcrd178.pdf&ei=4dSKUN_7B6bp0gGukYGIBQ&usg=AFQjCNHHlzQ68WY1xuiuUPeWLhnvdFK7lA&sig2=e48S2mun--0BBoqewAqlFw
Scrolling down to near the bottom (pages 27 and 30) I see no nice
bumps in the heat capacity.
George H.
>
> Modelling the thermal energy looks like a good application for one of
> JT's fave tanh functions.
>
> Cheers
>
> Phil Hobbs
>
> --
> Dr Philip C D Hobbs
> Principal Consultant
> ElectroOptical Innovations LLC
> Optics, Electro-optics, Photonics, Analog Electronics
>
> 160 North State Road #203
> Briarcliff Manor NY 10510
>
> hobbs at electrooptical dot nethttp://electrooptical.net- Hide quoted text -
> Modelling the thermal energy looks like a good application for one of
> JT's fave tanh functions.
>
> Cheers
>
> Phil Hobbs
>
> --
> Dr Philip C D Hobbs
> Principal Consultant
> ElectroOptical Innovations LLC
> Optics, Electro-optics, Photonics, Analog Electronics
>
> 160 North State Road #203
> Briarcliff Manor NY 10510
>
Lord Androcles, Zeroth Earl of Medway
Oct 26, 2012, 2:56:07 PM10/26/12
to
"Helmut Wabnig" wrote in message
news:94hl88ls9ev6cjgap...@4ax.com...
=================================================
Temperate changes - metal expands or contracts - gap between
plates changes. For an air dielectric tuning capacitor, area between
plates also changes.
-- This message is brought to you from the keyboard of
Lord Androcles, Zeroth Earl of Medway
news:94hl88ls9ev6cjgap...@4ax.com...
Temperate changes - metal expands or contracts - gap between
plates changes. For an air dielectric tuning capacitor, area between
plates also changes.
-- This message is brought to you from the keyboard of
Lord Androcles, Zeroth Earl of Medway
Robert Baer
Oct 26, 2012, 6:56:53 PM10/26/12
to
John Larkin wrote:
>
>
> If a capacitor has a largish temperature coefficient (hundreds of PPM
> capacitance change per degree C maybe), what happens to a charged cap
> when the temperature changes? Presumably C*V stays constant, so the
> stored energy 0.5*C*V^2 changes.
>
> So, would the specific heat of the capacitor be different, as a
> function of whether it is charged or not?
>
>
Assuming that there is no loss due to leakage, it is absurd to state
>
>
> If a capacitor has a largish temperature coefficient (hundreds of PPM
> capacitance change per degree C maybe), what happens to a charged cap
> when the temperature changes? Presumably C*V stays constant, so the
> stored energy 0.5*C*V^2 changes.
>
> So, would the specific heat of the capacitor be different, as a
> function of whether it is charged or not?
>
>
that the stored energy changes - neither a temperature increase nor a
temperature decrease could possibly increase the stored energy.
Robert Baer
Oct 26, 2012, 6:57:54 PM10/26/12
to
Helmut Wabnig wrote:
> On Fri, 26 Oct 2012 08:32:18 -0700, John Larkin
> <jjla...@highNOTlandTHIStechnologyPART.com> wrote:
>
>>
>>
>> If a capacitor has a largish temperature coefficient (hundreds of PPM
>> capacitance change per degree C maybe), what happens to a charged cap
>> when the temperature changes? Presumably C*V stays constant, so the
>> stored energy 0.5*C*V^2 changes.
>
>
> Why should C*V be constant?
> w.
* Exactly!
> On Fri, 26 Oct 2012 08:32:18 -0700, John Larkin
> <jjla...@highNOTlandTHIStechnologyPART.com> wrote:
>
>>
>>
>> If a capacitor has a largish temperature coefficient (hundreds of PPM
>> capacitance change per degree C maybe), what happens to a charged cap
>> when the temperature changes? Presumably C*V stays constant, so the
>> stored energy 0.5*C*V^2 changes.
>
>
> Why should C*V be constant?
> w.
Big Dog
Oct 26, 2012, 6:14:01 PM10/26/12
to
means the amount of energy supplied to generate an incremental
temperature change. Here, the presumption is that the flow of energy in
or out of the system is what has generated that temperature change, and
in the process also changes the capacitance.
George Herold
Oct 26, 2012, 6:59:34 PM10/26/12
to
the electrical energy is ~10uJ (?) put in your own numbers.)
George H.
(for a long time I didn't 'know' that temperature was energy,
I could only connect them though this weird entropy factor
E=T*S (S=entropy))
Tim Williams
Oct 26, 2012, 6:59:41 PM10/26/12
to
"Syd Rumpo" <use...@nononono.co.uk> wrote in message
news:k6eee9$rjf$1...@dont-email.me...
approximation you could base on the small-signal or high-frequency
capacitance, where plate deflection is negligible), you would expect that,
at some large static potential, the capacitor would store such-and-such,
projecting Q = V*C on a straight line (constant C). If you actually
perform the experiment, you'll discover the graph of Q vs. V bends up,
i.e., C goes up with voltage, storing much more charge at that "large
static potential". The difference is the excess energy consumed by
deflecting the plates that distance, and that difference is exactly the
amount of mechanical energy*.
*Average. The real world has rate losses (ESR, damping of the springy
plates, etc.) and static losses (hysteresis of the spring, dielectric,
etc.), so the actual zero-to-one integral may be higher than the
one-to-zero path. If you obtain a loop in the Q vs. V plot, draw a
straight line through the diagonal corners and see how that compares.
Tim
--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms
news:k6eee9$rjf$1...@dont-email.me...
> In (say) a parallel plate air-gap capacitor, the plates will bend
> towards each other slightly as charge is added. Is the electrical
> energy stored the same as the mechanical energy which would be required
> to bend the uncharged plates by the same amount?
Not the same as, but in addition to. If the plates did not flex (an
> towards each other slightly as charge is added. Is the electrical
> energy stored the same as the mechanical energy which would be required
> to bend the uncharged plates by the same amount?
approximation you could base on the small-signal or high-frequency
capacitance, where plate deflection is negligible), you would expect that,
at some large static potential, the capacitor would store such-and-such,
projecting Q = V*C on a straight line (constant C). If you actually
perform the experiment, you'll discover the graph of Q vs. V bends up,
i.e., C goes up with voltage, storing much more charge at that "large
static potential". The difference is the excess energy consumed by
deflecting the plates that distance, and that difference is exactly the
amount of mechanical energy*.
*Average. The real world has rate losses (ESR, damping of the springy
plates, etc.) and static losses (hysteresis of the spring, dielectric,
etc.), so the actual zero-to-one integral may be higher than the
one-to-zero path. If you obtain a loop in the Q vs. V plot, draw a
straight line through the diagonal corners and see how that compares.
Tim
--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms
Larry Stones
Oct 27, 2012, 9:49:21 AM10/27/12
to
On Fri, 26 Oct 2012 17:14:01 -0500, Big Dog wrote:
> The question was about specific heat, which means the amount of energy
> supplied to generate an incremental temperature change. Here, the
> presumption is that the flow of energy in or out of the system is what
> has generated that temperature change, and in the process also changes
> the capacitance.
No imbecile, the datasheet for a capacitor tells user about the capacity
> The question was about specific heat, which means the amount of energy
> supplied to generate an incremental temperature change. Here, the
> presumption is that the flow of energy in or out of the system is what
> has generated that temperature change, and in the process also changes
> the capacitance.
available versus environmental changes, ie the temperature of the
component, the capacitor, dielectric and so on.
hanson
Oct 27, 2012, 1:48:08 PM10/27/12
to
"Larry Stones" <larr...@yahoo.com> wrote:
>
"Fatso", the wrinkled, scrawny assed "little bitch" with the
bark & fat loud-mouth of a "Big Dog" <big.fi...@gmail.com>
hence "Fatso", cranked itself, recited a text book & wrote:
>
The question was about specific heat, which means the
amount of energy supplied to generate an incremental
temperature change. Here, the presumption is that the
flow of energy in or out of the system is what has generated
that temperature change, and in the process also changes
the capacitance.
>
>
The question was about specific heat, which means the
amount of energy supplied to generate an incremental
temperature change. Here, the presumption is that the
flow of energy in or out of the system is what has generated
that temperature change, and in the process also changes
the capacitance.
>
"Larry Stones" wrote:
No imbecile, the datasheet for a capacitor tells user
about the capacity available versus environmental
changes, ie the temperature of the component, the
capacitor, dielectric and so on.
>
hanson wrote:
No imbecile, the datasheet for a capacitor tells user
about the capacity available versus environmental
changes, ie the temperature of the component, the
capacitor, dielectric and so on.
>
Stones listen. Fatso is of course right in his own
universe. Fatso sees himself as a fallen Angel
that landed in s.p. to teach the earthlings the laws
of how he perceives nature. Don't crank yourself
over Fatso's well meant ejaculates... ahahahaha...
Thanks for the laughs, guys... ahahanson
George Herold
Oct 29, 2012, 11:42:37 AM10/29/12
to
morning.
He noticed that the temperature scale was in C... I was reading in
K!
So it turns out those big heat capacity spikes are the solid-liquid
phase transition.
(The yokes on me :^)
George H.
>
> The interesting (physics-wise) way to compare materials is by the
> molar heat capacity. (Water is amazing in that regard.)
>
whit3rd
Oct 30, 2012, 2:42:25 PM10/30/12
to
On Friday, October 26, 2012 8:32:24 AM UTC-7, John Larkin wrote:
> If a capacitor has a largish temperature coefficient ...
A simpler system, the common rubber band, is
similar: a stretched rubber band has lower heat
capacity than a relaxed one.
Grab a rubber band, apply to lips for quick temperature
check. Then stretch it, apply to lips again (it gets hotter).
Let it stay stretched, until it approaches room temperature,
and then relax it. It gets cooler than room temperature.
So, you can imagine a system that acts as a heat pump using
the charge-dependence of the capacitor's specific heat.
Rube Goldberg or Heath Robinson can sketch out the
details...
> If a capacitor has a largish temperature coefficient ...
> So, would the specific heat of the capacitor be different, as a
> function of whether it is charged or not?
Yes, as others have replied, it would be different.
> function of whether it is charged or not?
A simpler system, the common rubber band, is
similar: a stretched rubber band has lower heat
capacity than a relaxed one.
Grab a rubber band, apply to lips for quick temperature
check. Then stretch it, apply to lips again (it gets hotter).
Let it stay stretched, until it approaches room temperature,
and then relax it. It gets cooler than room temperature.
So, you can imagine a system that acts as a heat pump using
the charge-dependence of the capacitor's specific heat.
Rube Goldberg or Heath Robinson can sketch out the
details...
Jasen Betts
Oct 31, 2012, 5:12:16 AM10/31/12
to
could be incorporated
--
⚂⚃ 100% natural
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