Question

Explain nordhim equation and matthiessen rule of electrical resistivity

Answer 1

Matthiessen's rule. An empirical rulewhich states that the total resistivity of a crystalline metallic specimen is the sum of the resistivity due to thermal agitation of the metal ions of the lattice and the resistivity due to the presence of imperfections in the crystal.

NORDHIM EQUATION:

The Fowler‐Nordheim (FN) equation predicts current density due to field emission, generally from metals that, due to closely spaced extraction grids or anodes, experience very high surface fields over small emission areas. For the transmission probability, typical field emission gradients are quite strong, so strong in fact that those electrons with a longitudinal energy close to the Fermi level are most likely to tunnel, even though the supply function is small there. The supply function itself is well approximated by its zero temperature limit. The triangular barrier model contains enough to anticipate through scaling arguments what the effects of the image charge potential should be. The image charge represents the metal looking back at a charge outside its surface. Field effects appear in thermal emission via the Schottky barrier lowering factor.