Say you had a circuit with a battery and a loop of wire somewhere in the middle of the circuit. The loop of wire is positioned so that it is free to rotate in a uniform magnetic field, and since a current is running through it, a torque will be supplied by the magnetic force allowing it to rotate. The rotation of the coil will cause a changing magnetic flux because the angle constantly changes. The circuit to begin with was a DC circuit, but if an expression were to be derived for the emf induced in the coil, it would be an alternating emf. Does the back emf alternate back and forth completely or does it only vary sinousidally every half a period much like the emf provided in DC generators?