One problem with some of the newer high-temperature superconductors is getting a

Question

One problem with some of the newer high-temperature superconductors is getting a large enough current density for practical use without causing the resistance to reappear. The maximum current density for which the material will remain a superconductor Is called the critical current density of the material. In 1987, IBM research labs had produced thin films with critical current densities 1.0 x 10^5 A/cm^2. (a) How much current could an 18-gauge wire of this material carry and still remain superconducting? (18-gauge has a nominal diameter of 1.02 mm.) A (b) Researchers are trying to develop superconductors with critical current densities of 1.0 X 10^6 A/cm^2. What diameter cylindrical wire of such a material would be needed to carry 948 A without losing its superconductivity? mm

Explanation / Answer

part 2 )

A = I / J = ( 948 ) / ( 1.0 * 10 ^ 6 A/cm^2)

A = 9.48 * 10 ^ -4 cm^2

A = pie * r ^2 so

r = sqrt ( A/ pie )

= sqrt ( 9.48 * 10 ^ -4 cm^2/3.14 )

r = 0.01737cm

d = 2 * r = 2 * 0.01737 = 0.3475 mm

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