Faraday's law in the integral form can be stated as $V = -d\Phi/dt$, where the right-hand side represents the rate of change of the magnetic flux and the left the voltage difference. In other words, a changing magnetic flux generates a voltage.
My question is if a constant voltage would generate a changing magnetic flux.
If it does, then why is a.c. used in transformers? Even for d.c. currents to flow, a voltage must be present, so if there was a d.c. current in the primary, then there would be a voltage, and so, by Faraday's law, a changing magnetic flux. Also, if a.c is required, then what equation says that only a changing current generates a magnetic field?
Finally, does Ampère's law work both ways? That is, does a circulating magnetic field produce a current flow?
Thanks for the answers.