Question

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?

Answer 1

The voltage would have dropped by `0.867 V` to cause this decrease in potential energy.

Explanation:

We use the definition of electric potential to do this one:

`"potential difference"=("work done")/("quantity of charge")`

or `V=W/q`

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 `25J` to `12J`".
This should read "the electric potential energy changes from `25J` to `12J`".
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

`V = (13J)/(15C)=0.867 "volts"`

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.