Two equal positive charges $(q)$ are placed at the vertices $B$ and $C$ of an isosceles triangle of base $a$ and height $h=3 \sqrt{3} a / 2$, as shown in the adjacent figure. When a charge $q^{\prime}$ is placed at $A$, it is found that at a point inside the triangle, the net electric field due to the three charges vanishes. If this point is at a height $h / 3$, then what is $q^{\prime}$ ?

• A

  $q^{\prime}=-3 \sqrt{3} q$
• Correct answer
  B

  $q^{\prime}=+3 \sqrt{3} q$
• C

  $q^{\prime}=+\sqrt{3} q$
• D

  $q^{\prime}=-\sqrt{3} q$

Hence, the correct answer is option: 'B'.