How ac generators and dc generators are alike and how they are different?

Answer 1

They both have rotor and stator windings. They create a magnetic field and move a coil of wire through it, thus producing electricity.
The AC generator rotates a mageting field inside the stator. As the poles have both a north and south end, the field generated in staor coils is an AC waveform, as the poles reverse the current at each half turn. The power for the rotating coils are supplied with DC current via slip rings and the (excitation) current can be varied to control the output.
A DC generator has the magnetic field supplied by the stator coils. The induced current of the rotor windings is taken from the rotating shaft via a commutator, a brush and secored contact area. The induced current therefore is only produced over a small arc of the rotor and thus has the same polarity, (albeit interrupted) DC.

Answer 2

They both convert mechanical power into electrical power.

DC generators have a static field winding and a rotating armature that has its current fed through a commutator, which is a set of copper segments connected via carbon brushes, which tend to need frequent replacement.

AC generators have the main winding in the stator, with a DC current in the rotor winding. In this case the commutator is replaced by smooth slip-rings, also fed by carbon brushes, but they last a lot longer. This is also the preferred generator for a car's electrical system, with a 6-diode rectifier

NEW

Both convert mechanical energy into electrical with the help of magnetic field.

In AC there is a slip ring but in DC there is a Split ring.

So in ac we get alternative current. Here alternate stands for the direction of flow. Current changes direction for every half rotation.

But in dc we have direct current. It means that current flows in the same direction for both half rotations.

Answer 3

For AC generators slip ring commutators are use but in case of dc generators split ring commutators are used for converting AC generated in the armature to DC