What is the primary function of a relay in electrical circuits?

• A. To store electrical energy
• B. To switch circuits using an electromagnet
• C. To regulate voltage
• D. To measure current

Answer: (B)

Relays switch electrical circuits using an electromagnet to operate contacts. When the control signal energizes the coil, magnetic force moves the contacts to open or close the circuit, allowing a small control current to control a larger load current. This provides electrical isolation between the control side and the load and lets you control high-power circuits with a low-power signal, which is essential in railway control and interlocking. The device isn’t meant for storing energy, so it isn’t used for energy storage like a capacitor or inductor. It also doesn’t regulate voltage—that’s the job of regulators—and it doesn’t measure current—that’s done by meters or sensors. So the primary function is to act as a switch controlled by an electromagnet.