Add questions for pset 10

_psets/10.md

+---
+title: Problem Set 10
+---
+
+## (13.1)
+
+### (a)
+
+{:.question}
+Estimate the diamagnetic susceptibility of a typical solid.
+
+### (b)
+
+{:.question}
+Using this, estimate the field strength needed to levitate a frog, assuming a gradient that drops to
+zero across the frog. Express your answer in teslas.
+
+
+## (13.2)
+
+{:.question}
+Estimate the size of the direct magnetic interaction energy between two adjacent free electrons in a
+solid, and compare this to the size of their electrostatic interaction energy. Remember that the
+field of a magnetic dipole $$\vec{m}$$ is
+
+$$
+\vec{B} = \frac{\mu_0}{4 \pi}
+    \left[ \frac{3 \hat{x} (\hat{x} \cdot \vec{m}) - \vec{m}}{|\vec{x}|^3} \right]
+$$
+
+
+## (13.3)
+
+{:.question}
+Using the equation for the energy in a magnetic field, describe why:
+
+### (a)
+
+{:.question}
+A permanent magnet is attracted to an unmagnetized ferromagnet.
+
+### (b)
+
+{:.question}
+The opposite poles of permanent magnets attract each other.
+
+
+## (13.4)
+
+{:.question}
+Estimate the saturation magnetization for iron at 0 K.
+
+
+## (13.5)
+
+### (a)
+
+{:.question}
+Show that the area enclosed in a hysteresis loop in the $$(B,H)$$ plane is equal to the energy
+dissipated in going around the loop.
+
+### (b)
+
+{:.question}
+Estimate the power dissipated if 1 kg of iron is cycled through a hysteresis loop at 60 Hz; the
+coercivity of iron is $$\num{4e3} \si{A/m}$$.
+
+
+## (13.6)
+
+{:.question}
+Approximately what current would be required in a straight wire to be able to erase a $$\gamma \text{-} Fe_2 O_3$$
+recording at a distance of 1 cm?