Question

Two point charges $+8q$ and $-2q$ are placed as shown in the figure.

The point where the electric field is zero is

• A. $x=l$
• B. $x=2l$
• C. $x=3l$
• D. $x=4l$

Answer 1

Answer: (B)

Let at a point $P$ at a distance $d$ from $-2q$ charge at which the electric field is zero.

$\therefore E_1=E_2$
$\frac{1}{4\pi {\epsilon }_0}\frac{8q}{{\left(l+d\right)}^2}=\frac{1}{4\pi {\epsilon }_0}\frac{2q}{d^2}$
$4d^2={\left(l+d\right)}^2$
$2d=l+d$
$d=l$
Hence, at $x=2l$, the electric field is zero due to given charge configuration.