@@ -85,7 +85,7 @@ where $R_{\rm H}=-\frac{1}{ne}$ is the _Hall coefficient. So by measuring the Ha
While most materials have $R_{\rm H}>0$, interestingly some materials are found to have $R_{\rm H}<0$. This would imply that the charge carriers either have a positive charge, or a negative mass. We will see later (chapter 17) how to interpret this.
## Exercises
### Exercise 1
### Exercise 1: Extracting quantities from basic Hall measurements
We apply a magnetic field $\bf B$ perpendicular to a planar sample that sits in the $xy$ plane. The sample has width $W$ in the $y$-direction, length $L$ in the $x$-direction and we apply a current $I$ along $x$.
1. Suppose we measure a Hall voltage $V_H$. Express the Hall resistance $R_{xy} = V_H/I$ in terms of the Hall resistivity $\rho_{xy}$. Also express $R_{xy}$ in terms of the Hall coefficient $R_H$.
