Chapter Two - Electric Field and Steady Current Flow in Conducting Media

Abstract

In considering electrostatic induction, the chapter established that the electric field, caused by charges outside of a conductor, induces charges on its surface in such a way that the total field vanishes at every point within the conducting medium. This means that the field, because of external charges, is not able to cause an ordered motion of either electrons or ions, and consequently, they move randomly as if these external charges were absent; also, the flow of current, can therefore, be calculated without any knowledge of a medium's dielectric properties. Using this principle, the chapter describes ordered motion of charge, current lines and tubes, relation between the current density and charge, and Ohm's law in differential form. The chapter highlights that the amount of charge entering a volume V in any time interval always equals the amount of charge leaving the volume in the same time interval. Using this principle of charge conservation, the chapter derives a system of equations of the field and current density j. This equation shows that vortices of the field j are located at points where the electric field has a component in the direction perpendicular to conductivity of the medium. It is useful to study the distribution of electrical charge that arises when steady current flows in a conducting and polarizable medium. The chapter discusses the principle of charge conservation, Coulomb's law, and Ohm's law and considers regular points where the extraneous field is absent, highlighting the activity at interfaces and take into account the effect of field.