Two insulating small spheres are rubbed against each other and placed 1 cm apart. If they attract ea

Question

Two insulating small spheres are rubbed against each other and placed 1 cm apart. If they attract each other with a force of 0⋅1 N, how many electrons were
transferred from one sphere to the other during rubbing ?

Professor PC Thomas Classes · Answer

$
F=0.1 \mathrm{~N}
$
$r=1 \mathrm{~cm}=10^{-2}$ (As they rubbed with each other. So the charge on each sphere are equal)
So, $\mathrm{F}=\frac{\mathrm{kq}_1 \mathrm{q}_2}{\mathrm{r}^2} \Rightarrow 0.1=\frac{\mathrm{kq}^2}{\left(10^{-2}ight)^2} \Rightarrow \mathrm{q}^2$
$
=\frac{0.1 	imes 10^{-4}}{9 	imes 10^9} \Rightarrow q^2=\frac{1}{9} 	imes 10^{-14} \Rightarrow q=\frac{1}{3} 	imes 10^{-7}
$
$1.6 	imes 10^{-19}C$  Carries by 1 electron\ 1C carried by $1 / 1.6 	imes 10^{-19}$
$
\begin{aligned}
& 0.33 	imes 10^{-7} 	ext {  carries by } \frac{1}{1.6 	imes 10^{-19}} 	imes 0.33 	imes 10^{-7} \
& =0.208 	imes 10^{12}=2.08 	imes 10^{11}
\end{aligned}
$