Engineering Physics

5.1 Introduction

The valence electrons of isolated metallic atoms are bound to the atoms, whereas in a metallic crystal they are not bound to any particular atom; they freely move in the spaces between the atoms. So, they are called free electrons. These free electrons participate in electrical conduction; hence they are called as conduction electrons. The metals possess some physical properties. They are:

1. Due to the existence of large number of free electrons, metals possess high electrical and thermal conductivities.
2. They obey Ohm’s law i.e., the current through a metal is proportional to the applied electric field.
3. The resistivity (ρ) is proportional to the fifth power of absolute temperature [i.e., ρ ∝ T⁵] at low temperatures, whereas resistivity ...