With this simple circuit, you can confirm the flow of current through AC wires without touching the hot wire. It is an ideal circuit to monitor Laptop charger, Battery charger etc. It is also useful to check the flow of current in concealed cables. The circuit gives an LED indication from a distance of 15 cms if current is flowing through a live wire.
Like all other forms of energy, electrical energy is the capacity to do work. Like other forms of energy, electrical energy can be converted into other forms such as light energy, heat energy etc. Energy can only be transferred when a difference in energy level exists.