Replot the copper data for $R_{\mathrm{c}}$ versus $T$ with a smaller temperature scale extending to $-300^{\circ} \mathrm{C}$, and extrapolate the line to the temperature axis. At what temperature would the resistance go to zero? What are the practical electrical implications for a conductor with zero resistance? [It is interesting to note that the value of $\alpha$ is roughly the same for many pure metals:
approximately $\frac{1}{273}$, or $0.004^{\circ} \mathrm{C}^{-1}$. This is the same as the value of the coefficient of expansion of an ideal gas. Also, some metals and alloys do become "superconductors" or have zero resistance, at low temperatures. Some "high-temperature" ceramic materials show superconductivity at liquid nitrogen temperatures $\left(77 \mathrm{~K}\right.$, or $-196^{\circ} \mathrm{C}$, or $-321{ }^{\circ} \mathrm{F}$ ).]