# Homework Help: Insulator/Conductor Question with picture

1. Oct 22, 2008

### swooshfactory

1. The problem statement, all variables and given/known data

http://i215.photobucket.com/albums/cc95/warrenm_2007/elec.jpg

Here is the problem: The red dots represent points of equal electric potential and the gray haze is the projected equipotential line. I am unsure about what happens to the electric field lines as they encounter the insulator and around the large conductor in the middle. If anyone could explain to me what is happening there, I would appreciate it.

2. Relevant equations

3. The attempt at a solution

I guess I would think that the insulator stops the electric field and that it does not transmit to the other side. It would I believe stop the electric field and given that there is no source for an electric field on the other side, I don't see why it would continue.

Around the large conductor in the middle, I would think that the electric field lines are feeding into the conductor unless they can go up the middle or around it to continue to the other side.

Also: does the insulator affect the field at all? The one point I have on the surface of the insulator looks a little fishy.

2. Oct 24, 2008

### JoAuSc

Your diagram looks a little confusing. Is this the result of lab work, a drawing you made to better understand things, or is it something else? Are all of the red dots supposed to have the same potential, or just those along the same gray hazy line?

Electric field lines are always perpendicular to conductors. This is because if the electric field was running sideways along the surface, this would move charges, and a split second later when those charges have reached their destination and everything was in equilibrium there would no longer be a sideways (transverse) component to the E-field. For an insulator, things are more complicated. Now, equipotential lines should be perpendicular to the E-field lines, so if we have a circular conductor the equipotential lines close to the conductor should be circular. Of course, if this is lab work it may not be that precise.

3. Oct 24, 2008

### swooshfactory

i guess it seemed more clear to me. all the red dots in a grey haze line were equipotential. it was for lab work, i replicated my data with paint. i already got the report turned in, so i don't still need help. thanks for replying though.