Answer
To keep charges flowing in a conducting medium, something (such as a battery or a generator) must maintain a difference in electric potential across the material.
Work Step by Step
This is discussed on page 431.
You can help us out by revising, improving and updating this answer.
Update this answerAfter you claim an answer you’ll have 24 hours to send in a draft. An editor will review the submission and either publish your submission or provide feedback.