A charge of #15 C# is passing through points A and B on a circuit. If the charge's electric potential changes from #25 J# to #12 J#, what is the voltage between points A and B?
We use the definition of electric potential to do this one:
The "work done" in this case refers to the change in electrical potential energy of the charge.
Note: In the problem, it states "the electric potential changes from
This should read "the electric potential energy changes from
The "electric potential" is another name for "voltage difference", and is measured in joules per coulomb (which is the same as volts).
Getting back to the question:
The voltage then must be
One last decision to make - since this was a positive charge, and the potential energy decreased, it must have moved through a reduction in potential. By definition, a positive charge increases in potential energy when it moves through an increase in potential.