E-Field of non-conducting plane

[Fanman22]

Three very large sheets are separated by equal distances of 20.0 cm (Fig. 22-42). The first and third sheets are very thin and nonconducting and have surface charge densities of +6.50 µC/m2 and -6.50 µC/m2, respectively. The middle sheet is conducting but has no net charge.

http://img.photobucket.com/albums/v225/Fanman22/22-42alt.gif

What is the electric field between the left and middle sheets?
What is the electric field between the middle and right sheets?

Since it says the sheets are very large, and there is only a 0.2m separation between the surfaces, it seems logical that the E-field can be considered as calculating the field at a point close to the surface with the following equation:

E = charge density / (2*epsilon) = 6.5e-6/(2*(8.85e-12)) = 3.67e5 N/C

But apparently that is wrong even though I am reading it straight from my text??

 

[OlderDan]

Three very large sheets are separated by equal distances of 20.0 cm (Fig. 22-42). The first and third sheets are very thin and nonconducting and have surface charge densities of +6.50 µC/m2 and -6.50 µC/m2, respectively. The middle sheet is conducting but has no net charge.

http://img.photobucket.com/albums/v225/Fanman22/22-42alt.gif

What is the electric field between the left and middle sheets?
What is the electric field between the middle and right sheets?

Since it says the sheets are very large, and there is only a 0.2m separation between the surfaces, it seems logical that the E-field can be considered as calculating the field at a point close to the surface with the following equation:

E = charge density / (2*epsilon) = 6.5e-6/(2*(8.85e-12)) = 3.67e5 N/C

But apparently that is wrong even though I am reading it straight from my text??

Perhaps you are not including all the charge that produces an electric field in that region. Think about the field for one plane of charge; then think about the field from multiple planes of charge.

 

[thepatientmental]

The electric field between the left and middle sheets would be 3.67e5 N/C, since the left sheet has a positive charge and the middle sheet is conducting and therefore has no net charge. This means that the electric field lines would point away from the left sheet and towards the middle sheet.

The electric field between the middle and right sheets would also be 3.67e5 N/C, since the middle sheet is conducting and has no net charge, and the right sheet has a negative charge. This means that the electric field lines would point away from the middle sheet and towards the right sheet.

Your calculation for the electric field is correct. It is possible that the solution provided may have made a mistake or used a different method for calculating the electric field. It is always a good idea to double check your calculations and make sure they are consistent with the given information and the equations provided in your textbook.