Charge Motion in Metals

Written by Will Rountree

Mobile Electron Sea

Metals, like all matter, are made of atoms. These atoms consist of a nucleus surrounded by electrons. The majority of metals have few electrons in the outer orbitals, and these valence electrons aren't tightly bound to the nucleus. As a result they are "free" and able to move through the material. The electrons aren't shared or transferred between atoms; they are available to all nuclei in the metal. Often there is only one free electron per atom, but that is all it takes to create a "sea" of electrons surrounding the atoms. Due to every atom lacking a negatively charged electron, the atoms are positively charged and remain bound together by the "sea." There is an even distribution of positive and negative charges, so the net electric field inside of metal is zero.

Charge Motion

Electrons naturally repel each other. When an electric field is applied to a metal, the mobile electrons begin to experience a force and accelerate. The electrons continue to accelerate until they collide with other objects in the mobile electron sea. This process continues to propagate throughout the metal for as long as an external field is applied to the metal.

An electron's average speed as it moves through the metal, v, is described as it's drift speed. The electron's ease in moving through the metal, μ, is known as the mobility.

History

This model for the motion of electrons in metal is credited to physicist Paul Drude, who first proposed the model in 1900 three years after J.J. Thompson discovered the electron. Dubbed the Drude Model, this theory was expanded by Hendrik Lorentz five years after it was introduced. After the development of quantum theory the model was updated from the previous classical version.

References

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/conins.html#c1 http://physics.bu.edu/~okctsui/PY543/1_notes_Drude_2013.pdf