This Relay Demonstration Unit allows the investigation and study of how a relay functions in a clear and practical manner. A useful property of this Demonstration Relay Unit is that the circuit powering the coil is easily seen to be completely separate from the circuit-switched on by the relay. This is one of the reasons relays are used where a safe low-voltage circuit can be used to control a high-voltage circuit. When a current flows through the coil an electromagnetic field is produced. This field attracts the iron armature whose end makes the contact, completing the circuit and illuminating the Lamp. When the current is switched off, the contact will open again, switching the circuit off.