Question

Three point charges $+q,+2 q$ and $-4 q$ where $q=0.1 \mu C$, are placed at the vertices of an equilateral triangle of side $10\, cm$ as shown in. The potential energy of the system is

• A. $3 \times 10^{-3} J$
• B. $-3 \times 10^{-3} J$
• C. $9 \times 10^{-3} J$
• D. $-9 \times 10^{-3} J$

Answer 1

Answer: (D)

$U \, \frac{1}{4\quad_{0}} \frac{2q^{2}}{a} \frac{8q^{2}}{a} \frac{4q^{2}}{a}$
$U \, \frac{1}{4\quad_{0}} \frac{10q^{2}}{a} $
$U \, \frac{9\,\,10^{9}\,\, \left(0.1\,\, 10^{ 6}\right)^{2}}{\frac{10}{100}|}$
U = - 9 × 10^-3J