Electric field at the surface of a conductor

[jakeham]

Homework Statement

Put in plain words: "In a static situation, the electric field at the surface of a conductor can have no component parallel to the surface, because this would violate the condition that the charges on the surface are at rest."
Would this same statement be a valid one for tha electric field at the surface of an insulator?

Homework Equations

The Attempt at a Solution

I can't understand the sentence, and can't figure out if it's valid for an insulator.

 

[Dick]

The charges in a conductor are mobile. If there is a parallel component of the electric field at the surface then it will cause the surface charges to move (hence not 'static'). The charges in an insulator are not mobile. So the argument doesn't hold.

 

[chaoseverlasting]

In a STATIC situation, the charges ARE at rest. The statement holds

 

[Dick]

In a STATIC situation, the charges ARE at rest. The statement holds

The 'statement' is that there is no E field component parallel to the surface of the body. In the insulating case the charges won't move even if there is an E field. Hence there CAN be a E field in the static case. Hence the statement does NOT hold.