\item $I = (\textrm{charge}) \cdot (\textrm{loops per time})
\stackrel{1/T=\omega_L/2\pi}{=}
(Ze)(\frac{1}{2\pi}\frac{-e}{2m}B)$\\
- $\mu=IA=I2\pi<\rho^2>=-\frac{Ze^2B}{4m}<\rho^2>$\\
+ $\mu=IA=I\pi<\rho^2>=-\frac{Ze^2B}{4m}<\rho^2>$\\
$<x^2>=<y^2>=<z^2> \Rightarrow <r^2>=3<x^2>=3<y^2>$\\
$<\rho^2>=<x^2>+<y^2>=\frac{2}{3}<r^2>$\\
$\mu=-\frac{Ze^2B}{6m}$
{\bf Hint:}
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 $T=0K$.
+ \item Calculate $j_c(R,T=0K)$ for a wire of Sn with a diameter of 1 mm
+ at $T=0K$.
The critical current and penetration depth at $T=0K$ are
$I_c=75\, A$ and $\lambda =300\cdot 10^{-10}\, m$.
\end{enumerate}
\Rightarrow dr=\lambda dx$, $r=\lambda x$
$\Rightarrow
I_c=j_c(R)2\pi \lambda^2 \exp(-R/\lambda) \int_0^R d(\frac{r}{\lambda})
- \, \frac{r}{\lambda} \exp(\frac{r}{\lambda})$
+ \, \frac{r}{\lambda} \exp(\frac{r}{\lambda})$\\
Integration by parts: $\int uv' = uv - \int vu'$\\
$\int xe^x dx = xe^x-\int e^x dx=xe^x-e^x+c=e^x(x-1)+c$\\
$\Rightarrow