Question

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

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

Answer 1

The correct option is D $-K\frac{e^2}{r^2}\hat{r}$

$F=k\frac{(-e)(+e)}{r^2}$

$=k\frac{e^2}{r^2}$

Now, $\stackrel{⟶}{F}$ is along $\left(\stackrel{⟶}{-r}\right)$

$\therefore \stackrel{⟶}{F}=\frac{k{e}^2}{r^2}(-\check{r})=\frac{-{ke}^2}{r^2}\hat{r}$