Electrical Resitance

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To what extent does the electrical resistance of a metal depend on its temperature?

 

[TTman]

To what extent does the electrical resistance of a metal depend on its
temperature?

Ever heard of Google ?

 

[George Herold]

To what extent does the electrical resistance of a metal depend on its temperature?

Gee that's kind of a broad question. Do you have any particular metal
in mind?

For pure metals at high temperatures the resistivity is roughly linear
with temperature. (A high temperature being defined as being greater
than the Debye temperature for that material.)

George H.

 

[Spehro Pefhany]

To what extent does the electrical resistance of a metal depend on its temperature?

It varies, by metal, purity, alloy, and temperature range (as well as
other factors such as annealing and external stresses and magnetic
field). Pure metals tend to increase more-or-less linearly with
temperature, around room temperature. Most (not all) alloys have lower
tempco than pure metals around room temperature. At very cold
temperatures more dramatic things tend to happen. For example:

https://encrypted-tbn1.gstatic.com/...iTvGR0sqDDWt7EZCRmZQSnhldly_xAzJo13-cxj_4H71w

or vs. temperature with under strong magnetic fields:-

http://ars.els-cdn.com/content/image/1-s2.0-S0011227598000034-gr14.gif


Or it might drop suddenly to exactly zero, depending. For example, I'm
told that if you cool U238 to 2.4 K and squish it enough (1.2GPa) the
resulting alpha phase will go superconducting.

Here is an interesting paper:-

http://tinyurl.com/afzzbsf

 

[mkr5000]

Ever heard of Google ?

of course he has smartass.

maybe everyone should just Google it and ignore newsgroups?

 

[mkr5000]

To what extent does the electrical resistance of a metal depend on its temperature?

and besides, both John and Spehro give better answers that anything you can Google. we're lucky they're active on this group.

 

[[email protected]]

To what extent does the electrical resistance of a metal depend on its temperature?

I'm assuming the test has ended and it's safe to pass this on:

See the video

 

[[email protected]]

Around +0.4% per degree C for lots of pure metals. Alloys can be other values,

including some near zero.

Actually that's not a good answer for people in the business of purity testing of metals by means of resistivity, tempco, and thermoelectric properties. They're expecting absolutely wild deviations with just parts per gazillion impurity concentrations...

 

[[email protected]]

I thought it was an excellent answer.

LOL- I'll concede a 'good'- but 'excellent' would be a stretch.

 

[George Herold]

I thought it was an excellent answer.

Chuckle*, No one will every accuse you of being overly modest.

I like knowing it's goes as ~T, then the change with T goes as about 1/
T
So I'd guess +0.33% at 300K.
(Alloy's are just screwed up metals from a 'certain' physics point of
view.)


George H.
*(I trust you will take this in the good spirit in which it is
offered.)

 

[George Herold]

We make our own current shunts. We start with a sheet of manganin and
have it punched or photo-etched to our design shape. Then we fold it,
anneal it, bond it to a heat sink, and terminate. The magic is to get
the transient response right, namely to keep the heatsink eddy current
effects down and have a near-zero hum pickup area. Most heat-sunk
shunts and resistors, like those Vishay things or the MIL metal-case
resistors, have ghastly time-domain behavior from eddy currents and
thermoelectrics. Open-air "railroad" shunts have huge hum profiles.

Cool, Do you use some folded design to keep the pick-up out?

I been thinking about these little diode temp sensors.

I worry about sticking different metals together,
it's not clear to me when I get 'battery/chemical action'
between two metals.

With the diodes I was thinking about wetting a bit of Al
and sticking the collector of a transistor to that.
There's then this Al/solder/transistor-lead sandwich.

George H.

 

[George Herold]

I'm just being objective. My reply was factually correct and nicely
hedged.




Pure platinum is +3920 PPM/K around room temp. Copper, silver, lead,
aluminum are all about the same. Nickel, occasionally used for RTDs,
is around 6000.

This is a nice graph
http://www.copper.org/resources/properties/cryogenic/images/Electrical-Resistivity.gif

From copper.org
There's lots of other graphs... I don't get the magneto-resistance
one.

George H.

 

[Sjouke Burry]

y testing of metals by means of resistivity, tempco, and
thermoelectric properties. They're expecting absolutely wild
deviations with just parts per gazillion impurity concentrations...

Cool, Do you use some folded design to keep the pick-up out?

I been thinking about these little diode temp sensors.

I worry about sticking different metals together,

cut
Well, then you should NOT use diodes, because they stick all sorts of
metal and semiconductors together.

 

[[email protected]]

We make our own current shunts. We start with a sheet of manganin and

have it punched or photo-etched to our design shape. Then we fold it,

anneal it, bond it to a heat sink, and terminate. The magic is to get

the transient response right, namely to keep the heatsink eddy current

effects down and have a near-zero hum pickup area. Most heat-sunk

shunts and resistors, like those Vishay things or the MIL metal-case

resistors, have ghastly time-domain behavior from eddy currents and

thermoelectrics. Open-air "railroad" shunts have huge hum profiles.

I'm just not following what that has to do with temperature dependence?

 

[Spehro Pefhany]

What might happen to the specific resistance of pure Pb when you
increase the temperature by a couple of °C, from, say, 4.2K to 6.2K?


Best regards,
Spehro Pefhany

 

[Phil Allison]

"mkr5000"

of course he has smartass.

** The OP is a very obvious troll - so TTman's reply is both appropriate &
polite.

OTOH, yours was totally smartarses and pig arrogant.

maybe everyone should just Google it and ignore newsgroups?

** When Google likely has the needed info - then that is where to go first.

OTOH - you can go straight into hell.



..... Phil

 

[George Herold]

---
I can find no reference to that, but since Pb has a transition
temperature of 7.175K,  I'd expect its resitivity to remain zero at
any temperature below that.

Am I missing something?

Hi John, I think Spehro was 'commenting' on your "Without exception"
statement.
If you'd said, "In general", instead....

George H.

 

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Copper's residual resistivity is very greatly affected by magnetic
impurities. Oxygen annealing to get rid of the unoxidized Fe improves
the low temperature resistivity by some enormous factor, like turning 4N
into the equivalent of 6N.

But all of the expensive wire is "oxygen free". ;-)

 

[Ralph Barone]

Hi John, I think Spehro was 'commenting' on your "Without exception"
statement.
If you'd said, "In general", instead....

George H.

So it increases by 3%, then

 

[Spehro Pefhany]

So it increases by 3%, then

LOL


Best regards,
Spehro Pefhany