An electron is moving around the nucleus of a hydrogen atom in a circular orbit of radius $r$. The Coulomb force $\overrightarrow{F}$ between the two is (where $K = \frac{1}{4\pi\varepsilon_0}$):

  • A
    $ - K\frac{e^2}{r^3}\hat{r}$
  • B
    $K\frac{e^2}{r^3}\vec{r}$
  • C
    $ - K\frac{e^2}{r^3}\vec{r}$
  • D
    $K\frac{e^2}{r^2}\hat{r}$

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