Two point charges q and -3q are kept 12 cm apart. The distance of the point from q on the line between two charges at which potential due to this system of charges is zero will be:

3 cm

The correct answer is Option (3) → 3 cm

The electric potential at a point,

$v=\frac{kq}{r}$

Total potential at point P,

$v_p=\frac{kq}{x}+\frac{k(-3q)}{12-x}=0$

$⇒\frac{kq}{x}=\frac{k3q}{12-x}$

$⇒\frac{1}{x}=\frac{3}{12-x}$

$⇒x=3cm$