Which of the following is true with regard to rectifiers?

The correct answer identifies an essential characteristic of rectifiers used in cathodic protection (CP) systems. A typical rectifying unit is designed to allow current to flow in one direction while presenting a high resistance to current flow in the opposite direction. This functionality is crucial for converting alternating current (AC) to direct current (DC), which is necessary in CP applications to protect pipelines from corrosion.

By only allowing current to pass through in one direction, rectifiers ensure that the electrical current effectively reaches the pipelines, providing the necessary protective current to mitigate corrosion processes. This conversion and directionality of current flow is fundamental to the operation of CP systems, which rely on establishing an electrical circuit that protects metallic structures buried in the ground.

In contrast, other options represent misunderstandings about the operational principles of rectifiers within CP systems. For instance, rectifiers are widely used in these systems rather than rarely, and current does not flow along several paths through the rectifying element, as the design of rectifiers limits current to a single directional flow. Furthermore, understanding where the current exits – through the anode or cathode rather than just the negative terminal – is key to grasping how CP systems function effectively.