How is an electrical relay best described?

An electrical relay is best described as a magnetically operated switch. This device uses an electromagnet to open or close a circuit, allowing control of a larger current or voltage with a smaller one. When an electric current passes through the relay's coil, it generates a magnetic field that attracts a movable armature, which then either completes or interrupts the circuit contacts. This mechanism allows for remote control of electrical devices and systems, making relays valuable in various applications, including automation, safety systems, and control panels.

The other options are not accurate in representing how an electrical relay functions. A manually operated switch relies on physical action by a person to operate, while a hydraulic control device uses fluid pressure rather than electrical signals. A mechanical toggle switch is a simple on/off switch that does not incorporate magnetic operation to control the circuit and does not provide the same functionality or benefits as a relay in the context of electrical engineering and circuitry.