To convert an AC generator into a DC generator, a split-ring type commutator must be used.
Explanation:
Commutator function:
A commutator is a device that reverses the direction of current in the armature coils every half rotation, ensuring the current flows in the same direction through the external circuit, which is the key difference between AC and DC.
AC generator uses slip rings:
In an AC generator, slip rings are used to maintain electrical contact with the rotating armature, allowing the current to flow out of the generator. However, slip rings don’t change the direction of the current, resulting in alternating current.
Why other options are incorrect:
(b) slip rings and brushes:
While slip rings are used in AC generators, they don’t convert AC to DC. They only facilitate the transfer of current from the rotating armature to the external circuit.
(c) a stronger magnetic field has to be used:
A stronger magnetic field would increase the generated voltage in both AC and DC generators, but it wouldn’t change the type of current (AC or DC).
(d) a rectangular wire loop has to be used:
The shape of the wire loop (rectangular or otherwise) doesn’t determine whether the generator produces AC or DC. The key difference lies in the presence of a commutator.