conductivity

Heat flows from the hot end to the cool end of the rod via conduction. As the distance from the burner flame increases, the temperature of the rod falls by a proportional amount. In a teakettle (bottom left), hot water rises and cold water descends until all the water reaches the same temperature through convection. A home heating lamp (bottom right) produces its heating effect by direct transfer of radiant energy.

conductivity, term applied to a variety of physical phenomena. In heat, conductivity is the quantity of heat passing per second through a slab of unit cross-sectional area when the temperature gradient between the two faces is unity. Electrical conductivity is the current or the quantity of electricity passing per second through a similar slab when the potential gradient is unity, and it is the reciprocal of the resistivity. In sound the conductivity of the orifice or neck of a resonator is the ratio of the area to the length of the orifice.