Physics - Electrostatics Question with Solution | TestHub

Given,

$A=+ \mathrm{3 }n\mathrm{C}=3\times {10}^{-\mathrm{9 }}\mathrm{C}$

$B=+ \mathrm{1 }n\mathrm{C}=1\times {10}^{-\mathrm{9 }}\mathrm{C}$

Distance,$r_1=5\mathrm{ c}\mathrm{m}=0.05\mathrm{ m}=5\times {10}^{-2}\mathrm{ m}$

Work done$\left(W\right)=U_B-U_A$

$=\frac{k{q}_1{q}_2}{r_2}-\frac{k{q}_1{q}_2}{r_1}$

Here,$r_2=r_1-1$

$r_2=5-1=4\mathrm{ c}\mathrm{m}=0.04\mathrm{ m}=4\times {10}^{-2}\mathrm{ m}$

$=k{q}_1{q}_2\left[\frac{1}{r_2}-\frac{1}{r_1}\right]$

$=9\times {10}^9\times 3\times {10}^{-9}\times 1\times {10}^{-9}$

$\left[\frac{1}{4\times {10}^{-2}}-\frac{1}{5\times {10}^{-2}}\right]$

$=\frac{27\times {10}^{-9}\times 1}{5\times 4\times {10}^{-2}}$

$=\frac{27}{20}\times {10}^{-7}$

$=1.35\times {10}^{-7}J$