这是一份bath巴斯大学PH30077/PH30078作业代写的成功案
$$
\frac{\epsilon-1}{\epsilon+2}=\frac{4 \pi}{3} n \alpha
$$
where $\alpha$ is the atomic polarizability and $n$ the number of atoms per unit volume. This formula predicts that the measurable quantity
$$
\frac{(\epsilon+2) n}{\epsilon-1}
$$
for a given substance should be approximately independent of external parameters, such as pressure and temperature. Note that weak coupling between the atoms corresponds to small $n \alpha$, so that
$$
\epsilon-1 \cong 4 \pi n \alpha .
$$
PH30077/PH30078 COURSE NOTES :
$$
\mathbf{F}{\mathrm{Con} p}=p \mathbf{B}=-\frac{I}{c} \oint d \mathbf{I}^{\prime} \times p \frac{\left(\mathbf{r}^{\prime}-\mathbf{r}\right)}{\left|\mathbf{r}-\mathbf{r}^{\prime}\right|^{3}} $$ We recognize $$ p \frac{\left(\mathbf{r}^{\prime}-\mathbf{r}\right)}{\left|\mathbf{r}-\mathbf{r}^{\prime}\right|^{3}}=\mathbf{B}{p}\left(\mathbf{r}^{\prime}\right)
$$
where $\mathbf{B}{p}\left(\mathbf{r}^{\prime}\right)$ is the magnetic field that would be produced at $\mathbf{r}^{\prime}$ by the hypothetical pole at $\mathbf{r}$. Thus, $$ \mathbf{F}{C \text { on } p}=-\frac{I}{c} \oint d \mathbf{l}^{\prime} \times \mathbf{B}_{p}\left(\mathbf{r}^{\prime}\right),
$$