A rectifier is a device that can convert Alternating current (AC) to Direct current (DC). This is a process called rectification. Many rectifiers in the 20th century were made of metals like copper, iron, and silver. Nowadays most are semiconductors.
Half-wave rectifiers only have one side of a waveform, while the full-wave rectifiers use both sides of a waveform. The left-hand side of the full-wave rectifier circuit consists of four diodes: a diode bridge. Half-wave current is a current that can only flow in alternate current, a full-wave current can flow both alternating current and direct current. 
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