<P> A rectifier is an electrical device that converts alternating current ( AC ) , which periodically reverses direction , to direct current ( DC ) , which flows in only one direction . The process is known as rectification , since it `` straightens '' the direction of current . Physically , rectifiers take a number of forms , including vacuum tube diodes , mercury - arc valves , stacks of copper and selenium oxide plates , semiconductor diodes , silicon - controlled rectifiers and other silicon - based semiconductor switches . Historically , even synchronous electromechanical switches and motors have been used . Early radio receivers , called crystal radios , used a `` cat 's whisker '' of fine wire pressing on a crystal of galena ( lead sulfide ) to serve as a point - contact rectifier or `` crystal detector '' . </P>
<P> A rectifier is an electrical device that converts alternating current ( AC ) , which periodically reverses direction , to direct current ( DC ) , which flows in only one direction . The process is known as rectification , since it `` straightens '' the direction of current . Physically , rectifiers take a number of forms , including vacuum tube diodes , mercury - arc valves , stacks of copper and selenium oxide plates , semiconductor diodes , silicon - controlled rectifiers and other silicon - based semiconductor switches . Historically , even synchronous electromechanical switches and motors have been used . Early radio receivers , called crystal radios , used a `` cat 's whisker '' of fine wire pressing on a crystal of galena ( lead sulfide ) to serve as a point - contact rectifier or `` crystal detector '' . </P>
machine which converts ac into dc is known as
machine which converts ac into dc is known as
rectifier
rectifier