How is alternating current produced in a generator?

In an AC generator an armature is rotated in a magnetic field. This induces an electric current in the armature.

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As the crank turns the armature rotates in the magnetic field. One side of the armature moves up, and the other side moves down. The up and down motion induces a current in the wire. The current is in opposite directions on two sides of the armature. After the armature turns halfway, each side of it reverses direction in the magnetic field. The side that moved up moves down, vice versa. The current is induced. As the Armature turns, slip rings turn with it. They are attached to the ends of the armature. As they turn, they make contact with the brushes. The brushes can be connected to the rest of the circuit. In this way, a generator becomes energy source.