Question

Two equal point charges each of $3\,\mu\,C$ are separated by a certain distance in metres. If they are located at $\left(\hat{i}+\hat{j}+\hat{k}\right)$ and $\left(2\hat{i}+3\hat{j}+\hat{k}\right)$ then the electrostatic force between them is

• A. $9 \times 10^{-3} N$
• B. $16.2 \times 10^{-3} N$
• C. $10^{-3} N$
• D. $9 \times 10^{-2} N$
• E. $3 \times 10^{-3} N$

Answer 1

Answer: (B)

The distance between two charges is $r =\sqrt{(2-1)^{2}+(3-1)^{2}+(1-1)^{2}}=\sqrt{5}$
By Coulomb's law, the force between two charges is $F =\frac{1}{4 \pi \epsilon_{0}} \frac{ q _{1} q _{2}}{ r ^{2}}=(9 \times$
$\left.10^{9}\right)\left(\frac{3 \times 10^{-6} \times 3 \times 10^{-6}}{5}\right)=16.2 \times 10^{-3} N$