This is because thin wires have a greater electrical resistance. They restrict the flow of electrons and lead to a heating effect - as the electrons move along, heat is generated and the wire warms up. Conductors Wire used in an electric circuit is usually made of copper as this carries an electric current very effectively. We say that copper is a good conductor of electricity. Materials which do not allow an electric current to flow well are called insulators.
Most metals are good conductors and materials such as plastic and rubber are good insulators.
An electrical circuit needs to be complete before an electric current will flow. A Switch A switch is a gap in the wires in an electric circuit. If the gap is closed, the electric current will flow around the circuit and we say the switch is on. If the gap is open, electricity cannot flow and the switch is off. The simple switch in the picture is made of a small wooden block, two pins attached to wires and a piece of springy metal.