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. $V=\sqrt{\frac{ q _{1} q _{2}}{4 \pi \varepsilon_{0} mr }}$
• B. $V =\sqrt{\frac{4 \pi \varepsilon_{0} mr }{ q _{1} q _{2}}}$
• C. $V=\sqrt{\frac{ q _{1} q _{2}}{2 \pi \varepsilon_{0} mr }}$
• D. $V=\sqrt{\frac{2 \pi \varepsilon_{0} m r}{q_{1} q_{2}}}$

Answer 1

Answer: (A)

$ \frac{ mV ^{2}}{ r }=\frac{1}{4 \pi \varepsilon_{0}} \frac{ q _{1} q _{2}}{ r ^{2}}$
$\Rightarrow V =\sqrt{\frac{ q _{1} q _{2}}{4 \pi \varepsilon_{0} mr }}$