Question

Two point charges $4\mu C$ and $9\mu C$ are separated by $30cm$. The distance of point from $4\mu C$ where the strength of the field is zero is

• A. $18cm$
• B. $16cm$
• C. $12cm$
• D. $8cm$

Answer 1

The correct option is C $12cm$

Let at a distance x E be zero.
$\therefore$ E due to $4\mu C=Edueto9\mu C$
$\Rightarrow \frac{k\left(4\mu c\right)}{x^2}=\frac{k\left(9\mu c\right)}{(30-x{)}^2}$

$\Rightarrow \frac{2\times {10}^{-3}}{x}=\frac{3\times {10}^{-3}}{30-x}$

$\Rightarrow 60-2x=3x$
$\Rightarrow x=12cm.$