As per the diagram a point charge $+q$ is placed at the origin $O$. Work done in taking another poin

Question

As per the diagram a point charge $+q$ is placed at the origin $O$. Work done in taking another point charge $-Q$ from the point $A$ [coordinates $(0, a)]$ to another point $B$ [coordinates ( $a, 0)$ ] along the straight path $A B$ is

Professor PC Thomas Classes · Answer

Work done is equal to zero because the potential of $A$ and $B$ are
the same i.e., $\frac{1}{4 \pi \varepsilon_{0}} \frac{q}{a}$.
No work is done if a particle does not change its potential energy.
i.e., initial potential energy = final potential energy.