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Re: [Phys-l] conductivity of metals



On Oct 24, 2006, at 8:27 PM, John Denker wrote:

When I speak of "conductivity", unless context requires otherwise,
I mean both thermal and electrical conductivity, in accordance with
the Wiedemann-Franz law, as previously discussed.

I neglect the small contribution to the thermal conductivity from
the underlying lattice. Also note that superconductors are a
huuuuge exception to the W-F law: the superfluid transports
charge but not entropy.

Relative values of k, for example, with respect to Cu, can be measured by students. I have never done this but here is what seems to be not very difficult. Perhaps a science project for a group of up to five motivated kids.

A thermos bottle contains water at 20 C. It is closed with a stopper. A thermistor is used to measure water temperature. A copper, partially immersed in water sticks out of the stopper, like a hook. The external end of the hook is in contact with a flame, for example, from a candle, for time during which the water temperature changes, for example, by 6 C. Then another wire (same geometry) is used and the experiment is repeated. I expect changes in temperature, for a constant duration, to be proportional to k. If dT for the second wire is 3 C then k of that wire is two times smaller than k of Cu. The wires should be rather thick and short. I would isolate them thermally along the path of thermal energy (as much as possible). The method can be tested by using two materials of known k. .

Ludwik Kowalski
Let the perfect not be the enemy of the good.