1. The problem statement, all variables and given/known data There is a picture of two possible set ups for a dynamo-- the only difference I can see is the direction in which the main shaft rotates. He says that it is a "self-excited dc generator" because the rotation of the shaft inside of the single loop coil provides the changing flux which provides the emf which provides the current for the dc circuit. 2. Relevant equations 3. The attempt at a solution I'm completely lost. First of all, if there is no magnetic field to begin which, how can there be any induced emf? There would be no reason for charge carriers to move unless there IS an external B-field, I would think... Secondly, how could the direction of rotation influence the emf in such a way that one direction of rotation produces no current while the other direction does?