\item Calculate the magnetic suscebtibility in a state $\phi$.
What term is responsible for the diamagnetic contribution?
{\bf Hint:} The magnetic suscebtibility is defined as
- $\chi=-\frac{1}{V}\frac{\partial^2 E}{\partial B^2}$.
+ $\chi=-\frac{1}{V}\mu_0\frac{\partial^2 E}{\partial B^2}$.
\item Assuming a spherically symmetric charge distribution the equality
$<\phi|x^2|\phi>=<\phi|y^2|\phi>=\frac{1}{3}<\phi|r^2|\phi>$
is valid. Rewrite the diamagnetic part of the suscebtibility