Question

Three point charges $q, q$ and $-2 q$ are placed at the comers of an equilateral triangle of side '$L$ '. Calculate work done by extemal force in moving all the charges far apart without acceleration

• A. $\frac{1}{4 \pi \varepsilon_{0}} \frac{3 q^{2}}{L}$
• B. $-\frac{1}{4 \pi \varepsilon_{0}} \frac{3 q^{2}}{L}$
• C. $\frac{1}{4 \pi \varepsilon_{0}} \frac{5 q^{2}}{L}$
• D. $-\frac{1}{4 \pi \varepsilon_{0}} \frac{5 q^{2}}{L}$

Answer 1

Answer: (A)

$U=\frac{k(q)(-2 q)}{L}+\frac{k(q)(q)}{L}+\frac{k(q)(-2 q)}{L}$
$U=\frac{-3 k q^{2}}{L}$
$U_{\propto}=0$
$W_{e t}=U_{\propto}-U=\frac{3 k q^{2}}{L}$