14 In what ways do these factors affect conductivity? Silver is one of the materials with the best conductivity at room temperature; however, copper is more widely used than silver in the production of wires because it is less expensive. Water normally found in nature is a conductor. Distilled or deionised water is not a conductor; for this reason, it is mainly used in laboratories and industries. path: percorso plug: spina shell: livello 48 elecTriciTy CONDUCTORS AND INSULATORS What is conductivity? Electric current is the result of the movement of electric charges along a path. This path consists of materials whose atoms contain a sufficient number of free electrons in their outer shell to let electricity flow. The ability of a material to allow the passage of electric current is called conductivity. Conductivity strictly depends on the number of free electrons in the atoms, and it is affected by factors like the size, shape, and temperature of a material . On the other hand, the property of a material to oppose resistance to the passage of current is called resistivity. Conducting and insulating materials A conductor is a material which has a high number of free electrons and thus allows the passage of electric current easily. Materials such as metals like aluminium, silver, copper, iron, and steel are good conductors; in particular, copper is widely employed in the production of electric wires and plugs . Liquids such as non-distilled water, sea water , and lemon juice are good conductors, as well as human and animal bodies. An insulator is a material whose electrons are strongly attached to the nucleus and for this reason do not allow current to pass. Plastic, rubber, wood, and glass do not allow the flow of current; for this reason, some of these materials are used to cover wires and plugs in order to insulate them and prevent electrocution. Superconductors A superconductor is a material which opposes almost no resistance to the passage of current. Superconductivity is a property of some materials, such as mercury or ceramic, which, when cooled down at very low temperatures, lose their resistivity. However, the cooling process needed to achieve superconductivity requires a high amount of energy; for this reason, superconductors are very expensive to obtain. Superconductors are employed in MRI (Magnetic Resonance Imaging) and NMRI (Nuclear Magnetic Resonance Imaging), in maglev trains, experimental nuclear fusion reactors, and high-energy particle accelerators.