Electrostatics of conductors

[hunneysaummya]

"In a static situation, the electric field of a conductor can have
no component parallel to the surface coz this would violate the condition
that the charges on the surface are at rest." would this statement be valid
for electric field at the surface of an insulator? Explain your answer and
the reason for any differences b/w the cases of a conductor and an
insulator.

So, first I thought that this statement won't be valid coz charges can't
move in an insulator but then I thought that these charges could be excess
charges and not mobile charge carriers. So, the statement should be valid.

 

[Delphi51]

Kind of a tricky question. The first sentence is incomplete. On a conductor, the charges are free to move and if there was an E along the surface it would cause the charges to move such that that E would be canceled out. In most cases this would be a uniform distribution of charge whose combined E at any point would be perpendicular to the surface.

On an insulator, the charges can't move. You could put a spot of charge in one place only and the resulting E would go out in all directions from that spot.

 

[nlightner]

The statement is valid for both conductors and insulators. In both cases, the charges on the surface are at rest and therefore, there can be no component of the electric field parallel to the surface. This is because if there were a parallel component of the electric field, it would exert a force on the charges, causing them to move. In a conductor, the charges are free to move and would redistribute themselves in response to this force, eventually canceling out the parallel component of the electric field. In an insulator, the charges are not free to move, but they can still redistribute themselves slightly, resulting in a similar cancellation of the parallel electric field component.

The main difference between conductors and insulators in this scenario is the presence of free charge carriers. In conductors, there are free electrons that can move in response to an applied electric field, while in insulators, there are no free charge carriers. However, both conductors and insulators can still have excess charges on their surfaces, which are responsible for creating the electric field. The key difference is that in conductors, these excess charges can move and redistribute themselves, while in insulators, they are fixed in place.

In summary, the statement is valid for both conductors and insulators because it is based on the fundamental principle that charges on a surface must be at rest in a static situation. The presence or absence of free charge carriers does not change this principle, but it does affect how the charges can respond to an applied electric field.