Question

Three charges $+q,-q$, and $+2 q$ are placed at the vertices of a right angled triangle (isosceles triangle) as shown. The net electrostatic energy of the configuration is

• A. $-\frac{k q^{2}}{a}(\sqrt{2}+1)$
• B. $\frac{k q^{2}}{a}(\sqrt{2}+1)$
• C. $-\frac{k q^{2}}{a}(\sqrt{2}-1)$
• D. None of these

Answer 1

Answer: (C)

$ U =\frac{k q^{2}}{a}\left(-1+2-\frac{2}{\sqrt{2}}\right) $
$=\frac{k q^{2}}{a}(1-\sqrt{2}) $
$\Rightarrow U=-\frac{k q^{2}}{a}(\sqrt{2}-1)$