Conductors, insulators and semi-conductors
i) An insulatoris a material or object which resists flow of heat (thermal insulator) or electrical charges (electrical insulators). Examples are paraffin, wood, rubber, plastics etc.
ii) Conductorsare materials that contain free electrons which carry an electrical charge from one point to another.
Examples are metals and non-metals like carbon, graphite etc.
iii) Semi-conductors are materials or objects which allow the flow of electrical heat or energy through them under certain conditions i.e. temperature. Examples are germanium, silicon, cadmium sulphide, gallium arsenide etc.