If an object with charge - 3 nC moves from a location that has a potential of - 20 V to a location with a potential of - 10 V, what has happened to the potential energy of the system?

The potential energy decreases.

Explanation:

Given-

Charge of the object, q = - 3nC

Initial potential, Vi = - 20V

Final potential, Vf = - 10V

Potential energy, U = ?

We know,

Potential, V = U/q

initial potential energy = Viq

= - 20V X - 3nC

= 60 nJ

Final potential energy = Vfq

= - 10V X - 3nC

= 30nJ

We can see that the potential energy decreases as the object moves from initial to final position which means that the work is done against the electric field.