# Electric Field extension through

1. Sep 20, 2011

1. The problem statement

1)Do electric fields extend through a vacuum?
2)Do electric fields extend through the interior of a insulator?
3)Do electric fields extend through the interior of a conductor?

I am just starting to understand electric fields but I am still very unsure, and am not sure if my thought process is right and going in the right direction.
1) YES, electric fields exist and can extend/propagate through a vacuum.
Reasoning: Why not there is no difference between a vacuum and space just that a vacuum has no air in it. Vacuums are still made of matter so the electric field should still extend into that space.

2) No, A insulator is an material that does not respond to an electric field. An insulator also completely resists the flow of electric charge.
Reasoning: The definition of an insulator says that they must not allow electric fields to propagate through them.

3) No, Coulomb's Law says that electrons repel so they will all be on the exterior of the conductor and Gauss Law says that the enclosed charge within that conductor will be zero so therefore there is no electric field in the conductor.
Reasoning: With a zero electric field inside ALWAYS then there is in essence never a field actually there at all.

Like I said I may be completely wrong on all of this! I am just learning about the properties of electric fields now. I have made my attempt to reason through the questions using facts I already have learned, but I am not sure if my answers are correct. I think they are correct but I could care less if they are correct I want to understand the correct reasoning behind WHY they are right just not that I am right.

2. Sep 20, 2011

### Staff: Mentor

(2) A capacitor is constructed by arranging two parallel plates separated by a vacuum or some insulating material (or materials). Different materials will give different capacitance values, and all being higher than with a vacuum separator.

3. Sep 20, 2011

### Staff: Mentor

The vacuum is not made of matter. But it does have properties that interact with (or support) electromagnetic fields, such as permittivity and permeability which together set the propagation velocity of changes in those fields to c.
Insulators do "respond" to electric fields. They simply don't have any free electrons to support current flow. The bound electrons can shift their average positions with respect to their host atoms or molecule centers, so they can become polarized and support a field of their own in response to an externally applied field. You might want to look up "dielectric".

4. Sep 20, 2011

Now I am very confused.
1)Yes.
But I have no idea what the true reasoning behind it is. I think it is because I can treat a vacuum like any other space so electric fields will extend through it, the vacuum just happens to be void of matter?

2)Yes.
The insulator will respond to electric fields so therefore a electric field will extend through it.

3) I am correct in my original thought? I have not found any information to believe the contrary.

5. Sep 20, 2011

### Staff: Mentor

The vacuum is just space devoid of matter (classically, anyways. Things get more interesting in quantum theory ). Fields exist throughout space. Fields do not require matter in order to exist in space, although they can be modified by its presence (particularly if the matter happens to carry charges).

For 2, the field would extend through the insulator whether or not it had charges to respond to it. The charges in the insulator merely interact with that field to modify it. Keep in mind that matter, no matter how solid it may appear, is mostly empty space!

For 3, mobile charges follow the dictates of any applied field, and move to find their minimum energy configuration. So a conducting object immersed in an electric field will have electrons move to the side nearest the + source of that field. The new field that results from this concentration of electric charges cancels the effects of the external field within the conductor -- the net field sums to zero within. Electrons will continue to move to balance this equation as long as a net field exists to drive them, so the end result is zero net field. The process is very fast, and when you're dealing with 'static electricity', the settling time is ignored.

6. Sep 20, 2011

1) Yes a vacuum is a space devoid of matter but that doesn't matter because fields still will extend through the space that is a vacuum.

2) Yes a insulator will allow a field to extend through it and because it is an insulator it will not modify it. Therefore the insulator will allow the electric field to extend through the interior of it.

3)No a conductor will interact with the field and cancel the field out creating a zero field which in effect is no field. but is the rational . . .
correct or is there a flaw in that.

Thanks for all the advice and direction!

7. Sep 20, 2011

### Staff: Mentor

Your (2) is still wrong. An insulator can modify the field within in; an insulator has charges which interact with the field. It's an insulator because the charges are not free to move extensively -- but they can shift a bit in response to an applied field.

8. Sep 20, 2011

So my yes and no responses are correct i just need to work on the reasoning behind part 2?

so is an insulator like a conductor in the fact that they will interact with a field but different from a conductor in the respect that it will not cancel out the charge so the field will still be present?
Any closer?

9. Sep 20, 2011

### Staff: Mentor

Essentially, yes.
The only difference between conductors and insulators is the degree of freedom of movement of the charges within them.

Conductors have mobile electrons in what is called the conduction band. These electrons are free to move away from their parent atoms, and can drift through the material. They are available for an external field to play with, and can move anywhere in the conductor that the field can push them against the attraction of the atoms they leave behind.

Insulators have no electrons that are free to leave their atoms (without a sufficiently large field to coerce them that is -- a big enough field will "break down" any insulator!). The electrons are bound to their atoms, but an external field can cause them to spend more time on one side of the atom than the other. The negative electrons and the positive nuclei then form, on average, tiny electric dipoles with a slightly positive side and a slightly negative side. The fields from all these atom dipoles can add up to a field of respectable value, and can partially negate the effects of the external field inside the insulator.

So insulators can partially cancel the effects of the external field within themselves. Conductors can do a much better job with their mobile electrons, and can completely cancel the field.