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Temperature and Conductivity
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Question:
Would Temperature Effect the Amount of Current Traveling Through
A Copper Wire?
Replies:
Yes, very much. There is even a name for a condition that when the copper
wire (or any material) is so cold that there is no resistance to electrical
flow. That condition is called superconductivity. The temperature that
copper doesn't have any resistance to flow is around -410 F (very, very
cold). The general rule is "the higher in temperature the wire is, the
higher the resistance to electrical flow. It would be nice to have no
resistance to electrical flow, but we can't always have copper at very cold
temperatures. That is why scientist are working on superconductors that
have no resistance to flow at higher temperatures. Currently most
superconductors are ceramics that can be superconducting at around -320 F.
That's still cold, but that is also the temperature of liquid nitrogen, so
if you keep the superconductor in a bath of liquid nitrogen, it will stay
superconducting.
If you go to your local library, you can ask the librarian to help you look
for a book on superconductors that is more for you age group (there are some
that are even too smart for my age group ;-)). Have fun exploring.
C. Murphy
Yes it will, assuming that you have a fixed voltage across the wire.
Here is an explanation. The current that you can put through a wire
depends on the voltage you apply and the "resistance" of the wire. In
fact, current = voltage/resistance.
If you keep the voltage constant (from a battery, for example), then your
question becomes: Does temperature affect resistance of a copper wire. The
answer is yes.
How and why?
Well, current is the sum effect of electrons moving through the copper
wire. When the wire heats up, for example, by a torch, it causes
increasing chaos in the wire. This chaos causes the electrons to bump
around more than before. Therefore, flow is with less ease. This means
that the copper wire now has a higher resistance. (This is true for all
metals except one! Can you find which one? Copper is not the answer! )
But by how much, you may ask. OK, most metals increase their electrical
resistivity by about 0.005 per degrees. So, if the resistivity of copper at
25 C is, say, 1, then at 500 C it will be 1+500x.005=3.5! This means if you
heat your wire to 500 C, then its resistance increases 3.5 time! The
current through it then drops by 3.5 times.
How do we experimentally show this? If you connect in series a battery to a
Variac (to adjust voltage) to a very long thin copper wire (coiled, maybe)
to a small light bulb, and then heat the copper, you will see that the
light dims. If you let the wire cool, the light brightens. This
experiment works better if you use iron instead of copper. Copper has high
thermal conductivity. It may be hard to get it hot and it cools down
fast. Iron is better, and in addition, its electrical resistivity is more
sensitive to temperature change than copper. You may want to discuss this
with your science teacher and he/she can help you further if you want to do
a demonstration for your class. You need to have the right combination of
battery, wire, wire material, and heat for it to work.
Good luck
Dr. Ali Khounsary
Yes, but only slightly at normal temperatures. The temperature coefficient of
copper at 20 deg C is only .00393. This means that a piece of wire with a
resistance of 1 ohm at 20 deg C would have a resistance of 1.00393 ohm at 21
deg C.
Bradburn
The resistance of metals increases as the temperature increases. So, given
a constant potential (voltage) applied across the wire, the current would
be smaller at higher temperature.
Richard Barrans Jr., Ph.D.
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Update: June 2012
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