Principale of opretion of a DC genertor?

Answer 1

I believe the question was meant to read: Principle of operation of a DC generator?

In short, a current will be created in a wire moving through a magnetic field or moving a magnet field past a wire. (Ampere's law) Either spinning a magnet (armature) inside a wire coil (field), or conversely, spinning a wire inside a set of magnets, will cause an electrical current to be generated in the wire. Because the current generated every 180 degrees of rotation changes direction, the output is actually AC current and needs to be "rectified" by either mechanical or solid state means such as a bridge rectifier.