of the wire. Assume, that the penetration depth $\lambda$ is much
smaller than the radius $R$ of the cylinder.
{\bf Hint:}
- Use the relation $I_c=\int_0^R dr \int_0^{2\pi} d\phi \, j_c(r)$
+ Use the relation $I_c=\int_0^R dr \int_0^{2\pi} d\phi \, j_c(r) r$
and integration by parts.
\item Calculate $j_c(R,T=0K)$ for a wire of Sn with a radius of 1 mm at $T=0K$.
The critical current and penetration depth at $T=0K$ are