How do diodes work in an AC circuit?
Diodes conduct only when forward biased and restrict the flow of charges when reverse biased.
Diodes conduct only when they are forward biased. Since, AC reverses it direction periodically, the diode conducts only in half cycles and insulates during the other cycles.
This property of a diode is used in rectification of AC into DC.
In that case, two diodes (for a center tap rectifier) or four diodes are used.