Write the principle of a rectifier.

(N/A) rectifier is an electrical device that converts alternating current $(AC)$,which periodically reverses direction,into direct current $(DC)$,which flows in only one direction.
The principle of a rectifier is based on the unidirectional property of a $p-n$ junction diode.
$A$ $p-n$ junction diode allows current to flow easily when it is forward-biased (low resistance) and blocks the flow of current when it is reverse-biased (high resistance).
By utilizing this property,the diode acts as a switch that conducts during the positive half-cycle of the $AC$ input and blocks during the negative half-cycle (or vice versa),thereby producing a pulsating $DC$ output.