Question

A point charge $q_1=+2\mu C$ is placed at the origin of co-ordinates. A second charge, $q_2=-3\mu C$,is placed on the x-axis at $x=100cm$. At what point (or points) on the x-axis will the absolute potential be zero?

• A. $x=40cm$ and $x=-200cm$
• B. $x=40cm$ only
• C. $x=-200cm$ only
• D. $x=80cm$ only

Answer 1

The correct option is A $x=40cm$ and $x=-200cm$

At a point x on x-axis , total potential is

$K\frac{2}{x}-K\frac{3}{x-100}=0$ $K=\frac{1}{4\pi ϵ}{10}^{-6}$

$2(x-100)-3x=0\Rightarrow x=-200cm$

Also if the point x is between the 2 charge, total potential at point x :

$K\frac{2}{x}-K\frac{3}{100-x}=0\Rightarrow 2(100-x)-3x=0\Rightarrow x=40cm$