# 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?

Jan 23, 2017

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 $V = \frac{W}{q}$

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

$V = \frac{13 J}{15 C} = 0.867 \text{volts}$

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.