How an Electric Field is affected by an Insulator

AI Thread Summary
The discussion revolves around calculating the electric field and total electric flux for a charged filament surrounded by a cardboard cylinder. The user successfully found the electric field at the surface of the cylinder but is confused about whether to multiply it by the cylinder's length, questioning if the uniform electric field applies in this scenario. There is also uncertainty regarding the properties of cardboard as an insulator and its effect on the electric field, particularly whether it can create dipoles that would reduce the field. The user seeks clarification on these points, especially concerning the dielectric constant of cardboard. Overall, the dialogue emphasizes the complexities of electric fields in the presence of insulating materials.
Iftekhar Uddin
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I looked through this forum post for an answer to my problem. It gave me enough insight to try and come to some conclusions but I'm still confused on some parts here and there about how I got my final answer.

1. Homework Statement
A uniformly charged, straight filament 7.70 m in length has a total positive charge of 2.00 µC. An uncharged cardboard cylinder 1.50 cm in length and 10.0 cm in radius surrounds the filament at its center, with the filament as the axis of the cylinder.
(a) Using reasonable approximations, find the electric field at the surface of the cylinder.

(b) Using reasonable approximations, find the total electric flux through the cylinder.

Homework Equations



The Electric Field of a filament is λ/2πRε
λ=Total charge/length

The Attempt at a Solution

(I got the solution but I have questions about part A)
[/B]
* I found that the answer to A was the electric field of a filament with r = .1m. I used this equation on an earlier problem that asked for the electric field at x distance away from the filament. But this is the same for this cardboard cylinder? I don't have to multiply it by the length of the cylinder? Why? The only reason I could think for this is that I'm finding a uniform E so I'm just finding E at a distance of R radially. Is that correct?

* Is cardboard not an insulator? If so, it doesn't affect the electric field at all? I thought that as an insulator it'd affect the electric field so that the outside surface of the insulator would have an E of 0.
 
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As far as I remember, The net electric field is less than the applied electric field because it will create dipoles and will have an electric field opposite to the applied so it becomes less. However it can never be zero inside or outside.

It should give you the dialectic constant of the cardboard.
Someone can confirm this.
 
Hmmm maybe I'm not far enough into physics for this because I got the right answer without adjusting for this dipole situation.
 

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