What is a relay?

• A. An electrically operated switch
• B. A manual switch
• C. A fuse
• D. A resistor

Answer: (A)

A relay is an electrically operated switch. It uses an electromagnet (a coil) to move contacts that open or close a circuit, allowing a small control signal to switch a larger load safely and with electrical isolation between the control side and the power side. This makes it possible to automate or remotely control high-current or high-voltage circuits using low-power signals, and you can have normally open or normally closed configurations depending on how the contacts are wired.

A manual switch is operated by hand and does not rely on an electromagnet. A fuse is a protective device that interrupts current when it gets too high, preventing damage. A resistor is a component that resists current to limit flow and does not function as a switch.