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Name: Alex
Status: educator
Grade: 6-8
Country: Canada
Date: Fall 2011


Question:
I wonder if you could help me understand thermal vs electrical conductivity in a copper rod. As far as electrical conductivity, if I make the copper rod part of a circuit, including a battery, light and switch, when I close the switch the light illuminates (apparently) instantaneously. However, if I were to hold one end of the rod, and touch the other to a candle flame, it will take seconds, or even minutes for me to feel warmth at my end. Am I correct in thinking that in copper, electrons are the main carriers of heat, as well as electrical charge? If electrons are indeed the agents of energy transfer in both cases, what accounts for this apparent difference in the rate at which the energy makes its way down the rod?

Replies:
Alex,

Heat is transferred through 3 major processes: conduction, convection, radiation. Radiation means transferring heat in the form of light, such as infrared. Convection means transferring heat through a medium like air. The air picks up heat from a high temperature surface, moves through space, and transfers the heat to a low temperature surface. Conduction is the transfer of heat by contact of two solid surfaces.

Electrical conduction is essentially how quickly the electrons (or some charge carrier) can move through the material.

A higher transmittance of electricity than heat suggests that electrons can move faster through copper than the conduction transfer of heat (since atomic physical contact has to occur).

Greg (Roberto Gregorius) Canisius College


Hi Alex,

Electrons are not the primary carriers of heat, as evident by the many things reasonably good at heat transfer but horrible conductors, such as glass. The entire mass of atoms in the material are involved in heat conduction, so it takes quite a while longer from atoms bumping/pushing into each other to conduct that thermal energy over some distance.

Don Yee


Simply put electric current travels via the electrons which move easily in a metal like copper. Heat on the other hand, must move entire atoms, not just electrons. This is harder to do and takes much longer to occur.

R. W. Avakian


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