Question

Solve this:
Two point charges +10 $\mu$C and +20 $\mu$C repel each other with a force of 100N. If a charge if - 2 $\mu$C is added to each charge, then force between them will become
(1) 72 N (2) 7.2 N
(3) 720 N (4) 100 N

Answer 1

Dear Student,
$$\begin{gathered} Given, \\ Q1=+10\mu C;Q2=+20\mu C \\ Q1\text{'}=+8\mu C;Q2\text{'}=+18\mu C \\ F1=\frac{kQ1Q2}{R^2},where,F1=100N;k=\frac{1}{4\pi {\epsilon }_o};R=dis\tan cebetweenthecharges \\ F2=\frac{kQ1\text{'}Q2\text{'}}{R^2};F2=? \\ \frac{k}{R^2}=\frac{Q1Q2}{F1}=\frac{Q1\text{'}Q2\text{'}}{F2} \\ F2=\frac{Q1\text{'}Q2\text{'}}{Q1Q2}\times F1=\frac{8\times 18}{10\times 20}\times 100=72NAns\left(1\right) \end{gathered}$$

Regards,