Question

Two point charges $+Q_1$ , and $Q_2$ repel each other with a force of $200N.Q_1$ is increased by $20\%$ and $Q_2$ is decreased by $20\%$ . The change in the force of repulsion between them if they are kept at their original positions will

• A. Decrease by $8N$
• B. Increase by $8N$
• C. Increase by $2N$
• D. Decrease by $2N$

Answer 1

The correct option is A Decrease by $8N$

Previous force is $200N$ So,

$200=\frac{k{Q}_1{Q}_2}{R^2}$

New force

$F=\frac{k\times 1.2Q_1\times 0.8Q_2}{R^2}$

$=\frac{0.96\times k{Q}_1{Q}_2}{R^2}$

$=0.96\times 200=192N$

Thus, force decreases by $8N$.