Question

Two equally charged pith balls $3cm$ apart repel each other with a force of $4\times {10}^{-5}N$. The charge on each ball is

• A. $2\times {10}^{9}C$
• B. $2\times {10}^{-9}C$
• C. $\frac{2}{3}\times {10}^{9}C$
• D. $\frac{2}{3}\times {10}^{-9}C$

Answer 1

Answer: (B)

$2\times {10}^{-9}C$

Let $q$ be the charge on each particle
$F=\frac{q_1{q}_2}{4\pi {ϵ}_0{r}^2}$
$⟹4\times {10}^{-5}=\frac{q^2\times 9\times {10}^9}{(3\times {10}^{-2}{)}^2}$
On solving, $q=2\times {10}^{-9}C$