Final answer:
The work done by the electrostatic force on a particle of charge q as it moves from a to b can be calculated using the equation W = -AU = -qAV.
Step-by-step explanation:
The work done by the electrostatic force on a particle of charge q as it moves from a to b can be calculated using the equation W = -AU = -qAV. Here, W represents the work done, U is the potential difference between the two points a and b, and V is the electric potential at point a. This expression allows us to express the work done in terms of q, the charge of the particle, and A, the electric potential difference between a and b.