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

Where HC(0) is the critical field at 0 K.
(a)Using the data in Table 20.7, calculate the critical magnetic fields for lead at 2.5 and 5.0 K.
(b)To what temperature must lead be cooled in a magnetic field of 15,000 A/m for it to be superconductive?

H (A/m) (teslas) (teslas) m) 0.90 80 0.007 15 100 1.14 0.033 1.34 30 150 200 1.41 50 0.10 0.30 60 300 1.48 0.63 70