Question

Three charges $Q_{0}, \, -q$ and $-q$ are placed at the vertices of an isosceles right angle triangle as in the figure. The net electrostatic potential energy is zero if $Q_{0}$ is equal to

• A. $\frac{q}{4}$
• B. $\frac{q}{\sqrt{8}}$
• C. $\sqrt{2}q$
• D. $q$

Answer 1

Answer: (B)

$U=\frac{K Q_{0} \left(- q\right)}{l}\times 2+\frac{K \left(- q\right) \left(- q\right)}{l \sqrt{2}}=0$
$\frac{K q}{l}\left[- 2 Q_{0} + \frac{q}{\sqrt{2}}\right]=0$
$\therefore $ $Q_{0}=\frac{q}{2 \sqrt{2}}=\frac{q}{\sqrt{8}}$