SOLUTION

A metal rectifier is an early type of semiconductor rectifier that uses a metal oxide as the semiconductor material.

Common types of metal rectifiers:

1. Copper Oxide Rectifiers: These use copper oxide as the semiconductor material.
2. Selenium Rectifiers: These use selenium as the semiconductor material.

How they work:

A metal rectifier consists of a metal plate (usually copper) coated with a thin layer of semiconductor material (copper oxide or selenium). When a voltage is applied across the device, current can flow in one direction (forward bias) but not in the other (reverse bias). This property is used to convert alternating current (AC) to direct current (DC).

• Gas tube rectifier: Uses a gas-filled tube and ionization to convert AC to DC.
• Silicon rectifier: Uses a semiconductor material (silicon) to convert AC to DC. This is the most common type of rectifier used today due to its small size, high efficiency, and low cost.