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An electron is moving round the nucleus of a hydrogen atom in a circular orbit of radius r. The coulomb force $\stackrel{\to }{F}$ between the two is (Where $K=\frac{1}{4\pi {\epsilon }_{0}}$)

(1) $-K\frac{{e}^{2}}{{r}^{3}}\stackrel{^}{r}$

(2) $K\frac{{e}^{2}}{{r}^{3}}\stackrel{\to }{r}$

(3) $-K\frac{{e}^{2}}{{r}^{3}}\stackrel{\to }{r}$

(4) $K\frac{{e}^{2}}{{r}^{2}}\stackrel{^}{r}$

PMT