Electric Potential Energy

Electrical potential energy is exactly what it sounds like. It's the potential energy an object has due to the Coulombic electric force. Since the electric force is conservative(the work done by this force on a charge is independent of the charge's total path), that means

This may not make sense yet but it can be explained intuitively. If we take a negative test charge and put it in the electrical field of a positive test charge and release the negative test charge, the test charge will go towards the positive test charge. This attraction means that positive work is done on the charge. To refresh, here is the equation for work.

The force done on the test charge is parallel to and in the same direction as its displacement, meaning positive work is done on the charge. Since the test charge was released from rest and it moved to the source charge, it gained kinetic energy and, by conservation of energy, lost potential energy. This can be verified by the equation above which states the work done by the electric force on a charge is the negative of the change in electrical potential energy of that charge. ​

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One thing to remember is that change in potential energy is always measured between two points, in practice, but can be simplified to one if you assume one of the points to be "infinitely far away".

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If we pulled the test charge away from the positive source charge, the test charge would experience a force opposite to its displacement, meaning negative work would be done on it. This, in turn, means that the electrical potential energy of the test charge would increase.

As always, the work done(and potential energy) is a scalar so you put it in the sign and magnitude of charges if you use this equation. As implicitly given, the SI unit for the work and potential energy is Joules(J).