Question

Three point charges $3nC,6nC$ and $9nC$ are placed at the corners of an equilateral triangle of side $0.1m$. The potential energy of the system is :

• A. $8910nJ$
• B. $89100mJ$
• C. $9910J$
• D. $99100KJ$

Answer 1

Answer: (A)

$8910nJ$

Given : $q_1=3\times {10}^{-9}C$ $q_2=6\times {10}^{-9}C$ $q_3=9\times {10}^{-9}C$ $r=0.1$ m

Potential energy of system $U=\frac{k}{r}[q_1{q}_2+q_2{q}_3+q_3{q}_1]$

$\therefore$ $U=\frac{9\times {10}^9}{0.1}\left[\right(3\left)\right(6)+(6\left)\right(9)+(9\left)\right(3\left)\right]\times {10}^{-18}$ $J$

$⟹$ $U=8910\times {10}^{-9}J=8910$ $nJ$