Question

A particle of mass $m$ carrying charge $q_1$ is revolving around a fixed charge $-q_2$ in a circular path of radius $r$. Calculate the period of revolution and its speed also.
Speed of particle

• A. $V=\sqrt{\frac{q_1{q}_2}{4\pi {\epsilon }_{0}mr}}$
• B. $V=\sqrt{\frac{4\pi {\epsilon }_{0}mr}{q_1{q}_2}}$
• C. $V=\sqrt{\frac{q_1{q}_2}{2\pi {\epsilon }_{0}mr}}$
• D. $V=\sqrt{\frac{2\pi {\epsilon }_{0}mr}{q_1{q}_2}}$

Answer 1

Answer: (A)

$\frac{m{V}^2}{r}=\frac{1}{4\pi {\epsilon }_0}\frac{q_1{q}_2}{r^2}$
$\Rightarrow V=\sqrt{\frac{q_1{q}_2}{4\pi {\epsilon }_{0}mr}}$