Chapter-3|Current Electricity| NCERT 12th Physics:
Electric Current in Conductors:
The electrical conductivity of a solid substance depends upon the number of free electron in it. In metals, this number is quite large (nearly 10²⁹/m³). Hence metal are good conductors of electricity.
In metals, the electric conduction occurs by the movement of negative charge Carriers (electrons) only. Where as in liquid and gases, it occurs by the moment of both the positive and negative charge Carriers (ions).