Question

The electrostatic force on a small sphere of charge $0.4\mu C$ due to another small sphere of charge $-0.8\mu C$ in the air is $0.2N$.
What is the distance between the two spheres?

Answer 1

Using Coulomb's Law,

$F=\frac{1}{4\pi {\epsilon }_0}\frac{q_1{q}_2}{r^2}$

$r^2=\frac{1}{4\pi {\epsilon }_0}\frac{q_1{q}_2}{F}$

$r^2=\frac{9\times {10}^9\times 0.4\times \left(0.8\right)\times {10}^{-12}}{0.2}$

[Here $q_1=0.4\mu C;q_2=-0.8\mu C;F=0.2N]$

$r^2=14.4\times {10}^{-3}$

$=144\times {10}^{-4}$

So, $r=12\times {10}^{-2}$

$r=12cm$