Question

which is used to unidirectional current in an external circuit?

Answer 1

Answer:

Two methods are generally used:

1 - use rectifier diodes which only let current flow in one direction. Each time the AC voltage passes through zero, the diode facing the load will conduct current creating an average DC current.

2 - The use of a Comutator that rotates with the generator shaft and carbon brushes that switch the direction of current flow synchronously with the AC voltage waveform.