ABSTRACT
This chapter considers electrical conductivity since it provides a basis for the more complex ideas of thermal properties. Electrical conductivity is defined as the current per unit cross-sectional area of a conductor per unit voltage gradient along the conductor, and hence has units of reciprocal ohm.m. In metals, heat transfer follows much the same general principle as electrical conductivity although it is not the bodily movement of electrons but rather the transference of energy between them by collision. Since both thermal and electrical conductivities have their origins in the same structural features they are roughly proportional. Thermal conductivity is defined as the rate of heat transfer across a unit area of a material due a unit temperature gradient. The thermal conductivity of non-metals is more complex still, since it involves energy transfer between the atoms that make up the material. Thermal expansion of a material results from increased vibration of the atoms when they gain thermal energy.
