Question

Potential energy of two charges $10nC$ each separated by a distance of 0.09 m in air is

• A. $10\mu J$
• B. $1\mu J$
• C. $10mJ$
• D. $10J$

Answer 1

Answer: (A)

Potential energy of two charge system is given by
$U=\frac{1}{4\pi e_0{e}_r}\times \frac{q_1{q}_2}{r}$
Here, $q_1=q_2=10nC=10\times 10^{-9}C$
$\frac{1}{4\pi e_0}=9\times 10^{9}N{m}^2{C}^{-2}r=r=0.09m$
$\therefore U=9\times 10^9\times \frac{10\times 10^{-9}\times 10\times 10^{-9}}{0.09}=10\mu J$