Physics - Electrostatics Question with Solution | TestHub

${\text{w}}_{\text{ext}}=\Delta \text{u}={\text{u}}_{\text{f}}-{\text{u}}_{\text{i}}$

Here,$\text{u}=\frac{{\text{q}}_1{\text{q}}_2}{4\pi {\epsilon }_0\text{r}}$

${\text{u}}_{\text{i}}=\frac{\left(5\times 10^{-6}\right)\left(10\times 10^{-6}\right)}{4\pi {\epsilon }_0\left(1\right)}$

$=9\times 10^9\times 5\times 10^{-6}\times 10\times 10^{-6}$

Similarly,

${\text{u}}_{\text{f}}=\frac{9\times 10^9\times 5\times 10^{-6}\times 10\times 10^{-6}}{\text{0.5}}$

$\therefore {\text{W}}_{\text{ext}}={\text{u}}_{\text{f}}-{\text{u}}_{\text{i}}=\text{0.45 J}$