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# An electron is moving round the nucleus of a hydrogen atom in a circular orbit of radius r . Find the coulomb force $\;\overrightarrow{F}\;$ between the two

$(a)\;\large\frac{ke^2}{r^2}\;\hat{r}\qquad(b)\;\large\frac{ke^2}{r^3}\;\overrightarrow{r}\qquad(c)\;-\large\frac{ke^2}{r^3}\;\hat{r}\qquad(d)\;-\large\frac{ke^2}{r^3}\;\overrightarrow{r}$

Answer :  $\;-\large\frac{ke^2}{r^3}\;\overrightarrow{r}$
Explanation :
$\overrightarrow{F}=\large\frac{kq_{1}q_{2}}{|r|^3}\;\overrightarrow{r}$
$\overrightarrow{F}=\large\frac{k e (-e)}{r^3}\;\overrightarrow{r}$
$=-\large\frac{ke^2}{r^3}\;\overrightarrow{r}\;.$

edited Mar 24, 2014