Question

what is the difference between ac or dc generator.plzzzzzzz help me

Answer 1

Ac will generate alternating current alternation will depend on speed of the generator (turbine).
Dc current is direct current which can be generated by the alternator than we have to rectify for dc. the other sources is batteries.

Answer 2

AC generator generators alternating current that flows in one direction in one half of the cycle and the other way, in the other half cycle.  There are rotors, stators, rotating coil, load and permanent magnets in the AC generator.

DC generator Also has same structure as the AC generator.  In addition, it uses a commutator ring. The direction of the current flow is reversed exactly at half cycles of the potential generated due to induction.  So the final current that flows into the load is always in one direction.  Then additional electrical circuits (including capacitors) are used to bring the varying sine wave shape to a reasonably constant voltage level.