A charged particle of charge $Q $ is held fixed and another charged particle of mass $m$ and charge $q$ (of the same sign) is released from a distance $r.$ The impulse of the force exerted by the external agent on the fixed charge by the time distance between $Q$ and $q$ becomes $2r$ is
A charged particle of charge $Q $ is held fixed and another charged particle of mass $m$ and charge $q$ (of the same sign) is released from a distance $r.$ The impulse of the force exerted by the external agent on the fixed charge by the time distance between $Q$ and $q$ becomes $2r$ is
- A
$\sqrt {\frac{{Qq}}{{4\pi { \in _0}mr}}} $
- B
$\sqrt {\frac{{Qqm}}{{4\pi { \in _0}r}}} $
- C
$\sqrt {\frac{{Qqm}}{{\pi { \in _0}r}}} $
- D
$\sqrt {\frac{{Qqm}}{{2\pi { \in _0}r}}} $
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