Question

Two point charges +2q and -q are placed at (-a, 0) and (+a, 0) along X-axis respectively. Which of the following graph correctly shows potential as a function of position along x-axis?

• A.
• B.
• C.
• D.

Answer 1

The correct option is D

Potential at a point $-a<r<+a$, where $r$ is the distance of the point from the origin is given by:

$V_r=\frac{q}{4\pi {ϵ}_o}.\left(\frac{a-3r}{a^2-r^2}\right)$

So, at $r=0$, we have $V_{r=0}=\frac{q}{4\pi {ϵ}_{o}a}$
$\Rightarrow V_{r=0}$ have some positive value.
Since, (d) is the only option having positive value of potential at origin, it is the only correct option.