The relay switch

Sometimes it is useful to be able to control the current flowing in one circuit by using a second circuit. This is especially true if the current flowing in the first circuit is large. This can be done by using a relay switch.
In figure 6, when switch A is closed, the iron core of the coil becomes magnetized and attracts the iron armature. As the end of the armature (B) is attracted, its other end pushes the wires at C together, turning the second circuit on.
If switch A is opened, the electromagnet loses its magnetism, the armature returns to its original position and the second circuit is turned off.