Question

Two charges $2C$ and $6C$ are separated by a finite distance. If a charge of $-4C$ is added to each of them, The initial force of $12\times {10}^{3}N$ will change to :

• A. $4\times {10}^{3}N$ repulsion
• B. $4\times {10}^{2}N$ repulsion
• C. $6\times {10}^{3}N$ attraction
• D. $4\times {10}^{3}N$ attraction

Answer 1

The correct option is D $4\times {10}^{3}N$ attraction

Given initial force $=12\times {10}^3$
$\Rightarrow \frac{k\left(2\right)\left(6\right)}{x^2}=12\times {10}^3$
when a charge of $-4c$ is added to each of them
$F_{new}=\frac{k(-2)\left(2\right)}{x^2}$

(Putting value of $x^2$ from above equation)

$=\frac{k(-2)\left(2\right)}{k\left(2\right)\left(6\right)}\times 12\times {10}^3$

$F_{new}=-4\times {10}^{3}N$ (negative sign implies attraction)