Question

A point charge $q_0$ is placed at $r$ distance from long line charge. The line charge has uniform distribution of charges. Force by point charge on long line charge is proportional to

• A. $r$
• B. $r^{-1}$
• C. $r^{-2}$
• D. $r^{-3}$

Answer 1

The correct option is B $r^{-1}$

$F_{\text{on point charge}}=q_{0}E$
$=q_0$ $E$ (due to line charge)
$=q_0\frac{\lambda }{2\pi {ϵ}_{o}r}$
$F\propto \frac{1}{r}$ (By Newton's third law, force on rod is same)