For a superconducting material at a temperature T below the critical temperature Tc, the critical field HC(T), depends on temperature according to the relationship HC(T)=HC(0)(1TC2T2) where Hc(0) is the critical field at 0K. (a) Using the data in Table 20.7, calculate the critical magnetic fields for lead at 2.5 and 5.0K. (b) To what temperature must lead be cooled in a magnetic field of 15,000A/m for it to be superconductive? Compounds and Alloys b Ceramic Compounds \begin{tabular}{lr} YBaCu3O7 & 92 \\ Bi2Sr2Ca2Cu2O10 & 110 \\ T2Ba2Ca2Cu3O10 & 125 \\ HgBa2Ca2Cu2O8 & 153 \\ \hline \end{tabular}