Pre-Quantum Electrodynamics

• PM 10.7
• Gr 4.1

In a macroscopic sample subjected to an external electrostatic field, a complicated microscopic dance is induced among the constituent charges. As a result, local induced/permanent dipole moments tend to somewhat cancel each other, leaving a residual polarization. The leading remnant can be captured in a vector called the polarization and defined as \[ {\bf P} \equiv ~\mbox{dipole moment per unit volume} \]

Though it's important to remember that one could also talk about higher moments than dipole moments, for virtually all practical purposes the polarization is sufficient.