What principle does a relay operate on?

A relay operates on the principle of electromagnetic induction. In a relay, an electromagnetic coil is energized when a current flows through it, creating a magnetic field. This magnetic field attracts a movable armature, which then opens or closes a set of contacts, enabling or disabling the circuit connected to the relay. The use of electromagnetic induction allows a small control signal to operate a larger load, making relays essential in various electrical applications for controlling higher power devices.

The other options do not pertain to how a relay functions. Thermal conduction relates to heat transfer and is not involved in the operation of electrical circuits in the way relays operate. Mechanical leverage involves the use of physical force applied to achieve movement or amplification, but relays do not rely on physical leverage for switching mechanisms. Capacitive reactance relates to how capacitors store and release energy in AC circuits, which is also unrelated to the operation of relays.