Question

Two charges 9q and q are separated by distance 30 cm where the point on line joining them should be taken
so resultant field becomes zero

Answer 1

Using

$\huge \blue{x = \frac{ \sqrt{q1} }{ \sqrt{q1} + \sqrt{q2} }}$

$x = \frac{ \sqrt{9q} }{ \sqrt{9q} + \sqrt{q} } \\ x = \frac{ 3 \sqrt{q} }{3 \sqrt{q} + \sqrt{q} } \\ \frac{3 \sqrt{q} }{ \sqrt{q}( 3 + 1) } \\ x = \frac{3}{4} \\ \underline \bold \pink{ = \frac{3}{4} cm \: from \: + q \: charge}$