Finding Electric Field at 35.6 cm from Charge Distribution

[notmetalenough]

I'm having trouble with this problem:

Consider a thin spherical shell of radius 14.5 cm with a total charge of +38.9 microCloumbs distributed uniformly on its surface. (Take radially outward as the positive direction.)

So I need to find the field at 35.6cm from the center of the charge distribution.

Since this r is bigger than the shell R

E= k_e * Q/ r^2 ; right?

E = 8.99*10^9 * (38.9 * 10^-6)/(0.356)^2; right?

I get 2759365.9260194. My answer is MN/C so I put 2.76

No dice. Did I miss something?

I also tried 0.276, 27.6, 276, 2760, 27600, 276000, and 2760000 to be sure that the program wasn't just disregarding which units it wanted.

 

[stunner5000pt]

according to Guass' Law, a spherical shell as a whole should be treated as a point charge. What is the distnace from the shell (as a whole) to the point where you want to evaluate the electric field?

 

[gnpatterson]

try 2759365.926 or 2 759 000 again as far as I can see you have calculated it correctly. Are you sure the numbers are right.

might the question really say that the point is 35.6 beyond the shell?

 

[notmetalenough]

according to Guass' Law, a spherical shell as a whole should be treated as a point charge. What is the distnace from the shell (as a whole) to the point where you want to evaluate the electric field?

I was under the impression that Gauss's Law said that the spherical shell is treated as a point charge at the center of the shell itself. But I tried all numbers of different radii, none of them would give the right answer (according to the homework website). I think I'll just address this with my professor directly.