Question
As per this diagram a point charge +q is placed at the origin O. Work done in taking another point charge -Q from the point A [coordinates (O, a)] to another point B [coordinates (a, O)] along the straight path AB is
zero
Solution
A.
zero
The work done in carrying a test charge consists in product of difference of potentials at points A and B and value of test charge.
Potential at A
Potential at B
Thus, work done in carrying a test charge-Q from A to B
W = (VA - VB) ( -Q ) = 0