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FatoonsBaby71
Mar22-09, 11:51 AM
1. The problem statement, all variables and given/known data
A uniform line charge of density pl = 1nC/m is arrange in the form of a square 6m on a side. (In the z plane) Find the potential at (0,0,5) m

Answer:35.6 V

2. Relevant equations
R = The distance from the line to the point (0,0,5)
dL = ax dx + ay dy + az dz

3. The attempt at a solution
Well any point on the uniform line charge can be selected for this problem so I picked (0,3,0)
There for the distance is R= Sqrt((5-0)^2+ (0-3)^2)) Then I know that the potential of a charge distribution is equal to the integration of the whole volume of (p dV)/(4pi*Eo the Permittivity of free space*R)

Therefore, the x components dont matter because at both points they are zero. So I figured I would just integrate in terms of y get an answer and then integrate in terms of z and get an answer then the sum of those would be the total potential. However it doesn't seem to be coming out to the right answer.

Integral [0 to 3] pl/4pi*E0*R dy = 4.6241
Integral [0 to 5] pl/4pi*E0*R dz = 7.7068

does anyone know what I am doing wrong??
thanks for your help

jalalmalo
Mar22-09, 01:56 PM
I'm sorry I don't know the answer. I'm just wondering about the z-plane. what does that even mean. a palce has two axis

turin
Mar22-09, 03:42 PM
A uniform line charge of density pl = 1nC/m is arrange in the form of a square 6m on a side. (In the z plane) Find the potential at (0,0,5) mI think that your problem statement is missing some information. I assume that "the z plane" means the xy plane (i.e. the z=0 plane). I assume that the square of line charges is centered on the origin.

Well any point on the uniform line charge can be selected for this problem so I picked (0,3,0)This problem is not symmetric under exchange of any two points on the square. There is some symmetry, but that's not it.

FatoonsBaby71
Mar22-09, 08:38 PM
Yes, I was wrong the uniform line charge is in the x-y plane where z = 0.... I apologize.

So I really cant just pick a point on the line charge...i thought it wouldn't matter because it is uniformly distributed. Do you have any idea on how I could attack this problem??

turin
Mar23-09, 12:10 AM
So I really cant just pick a point on the line charge...i thought it wouldn't matter because it is uniformly distributed. Do you have any idea on how I could attack this problem??The uniformity makes the integrand simpler than if the distribution were generally nonuniform. Your hints are: integration and symmetry. Oh, and you may have a formula in your book for the potential due to a finite length of line charge, so think about that as a possibly alternative approach.