Thermal and Electrical Conductivity Processes
Date: Fall 2011
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?
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)
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.
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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Update: June 2012