71029

Possibility of a surface charge

We notę in particular that a surface charge density pscan exist, in many situations, even though not all.

It can, for example_; exist as a d.c. value on the surface of any materiał, i.e. a perfect

insulator, (after it has been rubbed with the cat), on a non-insulating imperfect conductor,

or on a perfect conductor.

It can also exist as an a.c. value on the surface of a perfect conductor or an imperfect

conductor, as even when surface currents are outlawed in the latter, volume currents

directed perpendicular to the surface can make a surface charge density change.

The case when psis outlawed is when the fields and other variables are all sinusoidal

and both materia Is are perfect insulators. There can in this situation be no mechanism

of charge transport to change the surface charge density.