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Conductors, Insulators and Semiconductors : |
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When an electric field is applied to any substance, the electrons can absorb energy from the field and can move to higher energy levels. However, this is possible only when empty states with higher energies exist close to the initial states in which the electrons happen to be in. If there is a substantial energy difference between the occupied electron state and the higher unoccupied state, the electron cannot absorb energy from the electric field and conduction cannot take place. Thus conduction takes place only in partially occupied bands. |
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In case of a metal, the bands which arise from different atomic orbitals overlap and the electrons can absorb energy from an electric field (or absorb thermal or light energy). The electrons in such partially filled bands are called free electrons . |
