Electric Potential Energy

Electric potential energy is the energy required to assemble a system of charged particles from an infinite distance. It is a function of the separation between the charges and the charge on each object in a system.

Consider a system of a negatively charged plate with static charges and a positive test charge. The attractive Coulomb force accelerates the test charge toward the static charge, decreasing the system's potential energy. Here, the movement of the test charge does not alter the electric field of the static charge.

This is similar to the free fall of an object under the influence of a gravitational force.

On the contrary, if a positive test charge moves toward a positively charged plate with static charges, the system's potential energy increases. However, the Coulomb force can be attractive or repulsive, unlike the gravitational force.

The Coulomb force is conservative, hence the work is expressed as a negative potential energy difference. The change in potential energy of the system is compensated by a change in kinetic energy.