What is the principal use of a relay in electronics?

A relay is primarily used to control a high-power circuit with a low-power signal. This component acts as an electrically operated switch that enables a small control current, often from a low-power circuit or signal, to activate a much larger current in a higher-power circuit. This functionality is crucial in various applications, enabling automation and safety in electrical systems.

When a low-power signal is applied to the relay's coil, it creates a magnetic field that pulls an armature to either complete or break the larger power circuit. This allows devices such as motors, heaters, and lights to be controlled remotely and safely, ensuring that operators do not have to deal directly with high-power circuitry.

The other choices involve different functions: amplifying signals pertains to increasing signal strength, rectification relates to converting AC to DC, and measuring resistance involves determining how much an object resists electrical flow. These tasks are performed by other specialized components, not relays, which solidifies the relay's role in enabling high-power control through low-power signals.