Physical Principles: Electromagnetics

Abstract

If electrostatic forces define the chemical shape of our world, to a great degree it is the movement of charge that brings that world to life. The movement of charge is necessary for sensation, mental activity, muscular movement, and energy transduction by photosynthesis and metabolism, to name just several examples. When an electric field exists in either free space or a conducting medium, charges will move under the field’s influence. This movement of charge is the electric current. The flow of charge in a vacuum is familiar to most readers as the electron beam of a television or oscilloscope. Movement of charge is more familiar today in the solid state, whether in metal or polymer conductors or in semiconductors. It is probable that within this generation the cathode ray tube will be of only historical interest, having most likely been replaced by solid state display devices. Movement of charge in the solid state is generally impeded by the presence of the atomic and molecular structure that composes the material through which charge flows. We will review the physical principles of conduction through conductors and semiconductors and then delve much more deeply into the molecular particulars of conduction in substrates of biological interest in later chapters.