Copper greater strength than monocrystalline forms. The softness of copper partly explains its high electrical conductivity (59.6×10 S/m) and high thermal conductivity, second highest (second only to silver) among pure metals at room temperature. This is because the resistivity to electron transport in metals at room temperature originates primarily from scattering of electrons on thermal vibrations of the lattice, which are relatively weak in a soft metal. The maximum permissible current density of copper in open air is approximately 3.1×10 A/m of cross-sectional area, above which it begins to heat excessively. Copper is one of a few metallic elements with a
Thermal conductivity containing "I" terms have to be zero. Now if we assume that where "δ" is the Dirac delta function, "I" terms get the following expressions By substituting these expressions to the equation for "λ", we see that it goes to zero. Therefore, "P"("x") has to be delta function. In an isotropic medium the thermal conductivity is the parameter "k" in the Fourier expression for the heat flux where formula_2 is the heat flux (amount of heat flowing per second and per unit area) and formula_66 the temperature gradient. The sign in the expression is chosen so that always "k" >