Question

The potential energy of system of two equal negative point charges of $2\mu C$ each held 1 m apart in air is ($k=9\times {10}^{9}SIunit$)

• A. $36J$
• B. $3.6\times {10}^{-3}J$
• C. $3.6J$
• D. $3.6\times {10}^{-2}J$

Answer 1

Answer: (D)

$3.6\times {10}^{-2}J$

The potential energy of system is
$U=k\frac{q_1{q}_2}{r}$
$U=k\frac{q^2}{r}$ $[q_1=q_2=q]$
or $U=9\times {10}^9\times \frac{(2\times {10}^{-6}{)}^2}{1}$
or $U=9\times {10}^9\times 4\times {10}^{-12}$
or $U=3.6\times {10}^{-2}J$